Results of the Interlaboratory Validation Study of EPA Method 1638 U. S. Environmental Protection Agency Office of Water Office of Science and Technology Engineering and Analysis Division Washington, DC 20460 December 2000 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 Acknowledgments This report was prepared under the direction of William A. Telliard and Maria Gomez Taylor of the Engineering and Analysis Division within the U. S. Environmental Protection Agency's ( EPA) Office of Water. The report was prepared by DynCorp I& ET with assistance from Interface, Inc. and Russell Roegner. EPA also acknowledges the efforts of the referee laboratory, participant laboratories, and especially the volunteer laboratories for their participation in the Interlaboratory Validation Study.

Disclaimer This report has been reviewed by the Analytical Methods Staff in the Engineering and Analysis Division within the U. S. EPA's Office of Water. Mention of company names, trade names, or commercial products does not constitute endorsement or recommendation for use.

Questions or comments regarding this report should be addressed to:

Maria Gomez Taylor Analytical Methods Staff ( 4303) Office of Science and Technology U. S. Environmental Protection Agency Ariel Rios Building 1200 Pennsylvania Avenue, N. W. Washington, DC 20460 202 260 1639 Requests for additional copies should be directed to:

USEPA NSCEP 11029 Kenwood Road Cincinnati, OH 45242 800 490 9198 http:// www. epa. gov/ ncepi Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 Results of the Interlaboratory Validation Study of EPA Method 1638 i Draft  December 2000 TABLE OF CONTENTS Acknowledgments List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Section 1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Section 2 Study Design and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.1 Phase 1  Laboratory Qualification ( MDL and Blank Analyses) . . . . . . . . . . . . . . . . . . . . . . 1 2.2 Phase 2  Sample Collection, Preparation, and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.3 Phase 3  Blind Sample and QC Sample Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Section 3 Study Management and Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Section 4 Data Reporting and Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1 Phase 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2 Phase 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.3 Phase 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.3.1 Calibration Verification Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.3.2 Initial Precision and Recovery Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.3.3 Ongoing Precision and Recovery Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.3.4 Blanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.3.5 Matrix Spike and Matrix Spike Duplicate Samples . . . . . . . . . . . . . . . . . . . . . 13 4.3.6 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.3.7 Standard Reference Material Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.3.8 Additional Deviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Section 5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1 Phase 1 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.2 Phase 2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.2.1 Background Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.2.2 Stability Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.3 Phase 3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.3.1 Outlier Screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.3.2 Calibration Linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.3.3 Calibration Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.3.4 Initial and Ongoing Precision and Recovery ( IPR/ OPR) . . . . . . . . . . . . . . . . 29 5.3.5 Matrix Spike and Matrix Spike Duplicate Analyses . . . . . . . . . . . . . . . . . . . . 31 5.3.6 Method Blank Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.3.7 Calibration Blank Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 5.3.8 Standard Reference Material Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 5.3.9 Quality Control Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 5.4 Silver Recoveries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 ii Section 6 Development of QC Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 6.1 Method Detection Limit ( MDL) and Minimum Level ( ML) . . . . . . . . . . . . . . . . . . . . . . . . 43 6.2 Calibration Linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 6.3 Calibration Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 6.4 Initial and Ongoing Precision and Recovery ( IPR/ OPR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6.5 Matrix Spike/ Matrix Spike Duplicate ( MS/ MSD) Recovery and Relative Percent Difference ( RPD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Section 7 Data Analysis and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.1 Matrix Specific Performance of Method 1638 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.2 Overall Performance of Method 1638 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Section 8 Conclusion and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Appendix A Study Plan for Collaborative Validation of Trace Metals Methods 1631, 1632, 1636, 1638, 1639, and 1640 Appendix B Data Submitted in the Interlaboratory Method 1638 Validation Study Appendix C Statistical Methods Results of the Interlaboratory Validation Study of EPA Method 1638 iii Draft  December 2000 LIST OF TABLES Table 2 1: Validation Study Samples Sent to Participating Laboratories . . . . . . . . . . . . . . . . . . . . . . . . . 3 Table 3 1: Laboratories Participating in the Method 1638 Validation Study . . . . . . . . . . . . . . . . . . . . . . 7 Table 4 1: Number and Type of Phase 3 Samples Analyzed by Participating Laboratories . . . . . . . . . . 10 Table 5 1: Phase 1, MDL and Method Blank Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table 5 2: Youden Outlier Laboratories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Table 5 3. Percentage of Sample Results Rejected as Grubbs Outliers . . . . . . . . . . . . . . . . . . . . . . . . . 22 Table 5 4. Laboratory 3 Calibration Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Table 5 5. Weighted Linear Regression Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Table 5 6. Percent Recoveries for Calibration Verification Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Table 5 7. Precision and Recovery Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Table 5 8. MS/ MSD Percent Recoveries and Relative Percent Differences Across Laboratories . . . . . . 31 Table 5 9. MS/ MSD Percent Recoveries and Relative Percent Differences Across Matrices . . . . . . . . . 33 Table 5 10. Method Blank Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Table 5 11. Calibration Blank Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Table 5 12. SRM Sample Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Table 5 13. Quality Control Sample Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Table 5 14. Recovery of Silver in QC and Field Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Table 6 1. Revised MDLs and MLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Table 6 2. Calibration Verification Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Table 6 3. IPR Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Table 6 4. OPR Verification Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Table 6 5. MS/ MSD Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Table 7 1. Pooled Matrix Specific Precision and Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Table 7 2. Laboratory Precision and Recovery Performance Using EPA Method 1638 . . . . . . . . . . . . . 52 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 iv Results of the Interlaboratory Validation Study of EPA Method 1638 v Draft  December 2000 Executive Summary This report presents results of EPA's interlaboratory validation study of draft Method 1638 Determination of Trace Elements in Ambient Waters by Inductively Coupled Plasma Mass Spectrometry ( EPA 821 R 96 005, January 1996; the " Method").

The objectives of the study were to evaluate the performance of the method and to gather data to allow revision of detection and quantitation limits and the quality control ( QC) acceptance criteria ( performance specifications).

The study was conducted in 1999 and managed by the Analytical Methods Staff in EPA's Office of Science and Technology. Day to day operations during the study were managed by the EPA Sample Control Center ( SCC), operated by DynCorp under contract to EPA.

A referee laboratory prepared the Study samples and shipped the samples to the laboratories. Eight laboratories participated. A total of 40, 16, and 32 samples were analyzed from reagent water, wastewater, and ambient water matrices, respectively. Results were transmitted to SCC where they were verified and entered into a database for statistical analysis. The statistical analysis yielded statements of Method performance and revised method detection limits ( MDLs), minimum levels of quantitation ( MLs) and QC acceptance criteria.

Study results demonstrated that Method 1638 produces reliable results by ICP MS and largely supported the performance specifications given in the draft method. The study also provided information regarding areas of the method that can be further clarified to ensure that all laboratories interpret requirements in the same way and suggested the need for a separate study of silver stability.

EPA plans to revise Method 1638 to reflect the results of this study and to propose the revised method for use at 40 CFR part 136. Results of the Interlaboratory Validation Study of EPA Method 1638 1Results of the Interlaboratory Validation Study of EPA Method 1631, March 1998. Available from the EPA Sample Control Center, 6101 Stevenson Ave., Alexandria, VA 22304; 703/ 461 2100.

2Guidelines for Selection and Validation of U. S. EPA's Measurement Methods, U. S. EPA Office of Acid Deposition, Environmental Monitoring and Quality Assurance ( OADEMQA), Office of Research and Development, U. S. EPA, August 1987, DRAFT.

3Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D 19 on Water ( ASTM D2777 96), September 1996.

4" Guidelines for Collaborative Study Procedure to Validate Characteristics of a Method of Analysis," J. Assoc. Off. Anal. Chem. 72, 694 704, 1989.

Draft  December 2000 1 Section 1 Background This report presents the design, results, and conclusions of an interlaboratory validation study of EPA Method 1638: The Method was developed in 1995 by EPA's Office of Water to address stakeholder needs for measuring metals at the concentrations specified in EPA and State water quality criteria.

The Office of Water ( OW) initiated the interlaboratory validation study in 1997 as part of a larger effort to validate all seven of the EPA 1600 series trace metals draft methods for application to aqueous matrices. Each of the methods had been widely distributed for review and comment, tested in several single laboratory studies, and revised accordingly.

To accommodate stakeholder interests, and to expand the scope of the study, the Electric Power Research Institute ( EPRI) funded the distribution of additional samples to study laboratories. EPA also prioritized its validation efforts to reflect the most pressing needs of the stakeholder community. Results of the Method 1631 study already have been reported ( Results of the Interlaboratory Validation Study of EPA Method 1631, March 1998), and results of the remaining studies will be reported as the studies are completed. 1 The remainder of this report focuses on the design, implementation, and results of the Method 1638 Interlaboratory Study ( the " Study").

Section 2 Study Design and Objectives The primary objectives of the study were to 1) characterize the performance of Method 1638 and 2) evaluate and, if appropriate, revise the quality control ( QC) acceptance criteria based on study results. The study was designed in accordance with interlaboratory validation study procedures published by EPA, 2 ASTM, 3 and AOAC International. 4 Details of the study design are summarized in Sections 2.1 through 2.3 below. Additional details can be found in the Study Plan for Collaborative Validation of Trace Metals Methods 1631, 1632, 1636, 1637, 1638, 1639, and 1640, February 1997 ( the " Study Plan") provided as Appendix A to this report.

The study was conducted in three phases: ( 1) Laboratory Qualification, ( 2) Sample Collection, Preparation, and Distribution, and ( 3) Blind Sample and QC Sample Analyses.

2.1 Phase 1  Laboratory Qualification ( MDL and Blank Analyses)

The objective of Phase 1 was to identify a minimum of nine laboratories capable of analyzing aqueous samples using Method 1638. This number was selected as a conservative figure likely to yield at least six sets of useable data after all outlier and data quality analyses had been completed. It was not considered Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 2 necessary for each laboratory to have extensive experience with the method; rather, laboratories were to have experience representative of the federal, state, local, and private laboratories that ultimately would use Method 1638 to measure antimony, cadmium, copper, lead, nickel, selenium, silver, thallium, and zinc ( the " target analytes") under the Clean Water Act and other environmental programs. EPA identified eleven laboratories that met these criteria. To assure that these laboratories were capable of performing the method, laboratories were provided up to 30 days to review Method 1638 and to perform method detection limit ( MDL) studies and blank analyses for the target analytes. Laboratories interested in participating on a volunteer basis were encouraged but not required to submit MDL study data.

MDL studies were performed according to the requirements given at 40 CFR 136, Appendix B, Definition and Procedure for the Determination of the Method Detection Limit, Revision 1.11. Reagent water was chosen as the reference matrix because it is homogeneous, readily available, and included as an option in the EPA MDL procedure. In accordance with these requirements, 10 of the 11 laboratories prepared and analyzed a minimum of 7 replicate samples containing each of the target analytes. Based on the MDL determinations, eight laboratories were identified to participate in Phase 3. Efforts to identify a ninth laboratory were determined to be unnecessary given the study schedule and costs.

2.2 Phase 2  Sample Collection, Preparation, and Distribution The study design included the use of a referee laboratory to collect, prepare and distribute samples to each of the participating laboratories. The primary objectives in using a referee laboratory were to 1) collect, prepare, and distribute freshwater, effluent, and reagent water samples that contained the target analytes of interest at the desired concentration levels, and 2) minimize variability within each of the sample matrices distributed to the participant laboratories.

In implementing Phase 2, the referee laboratory was directed to perform all sample collection, preparation, and distribution activities in accordance with sample handling and analysis procedures outlined in Method 1669: Sampling Ambient Water for Trace Metals at EPA Water Quality Criteria Levels ( EPA 821 R 96 008, July 1996) and Method 1638. The referee laboratory also was instructed to collect a sufficient volume of each sample to allow for 1) distribution of the various water samples to each of the eight participating laboratories, 2) stability analyses by the referee laboratory, 3) analysis of matrix spike ( MS) and matrix spike duplicate ( MSD) samples by each of the eight laboratories, and 4) extra volume in case of sample breakage, lost shipments, or other unforeseen problems.

After collecting bulk sample volumes from freshwater and effluent sources, the referee laboratory thoroughly homogenized each sample matrix before dividing it into sample aliquots for background determination and spiking under controlled clean room conditions. Background concentrations of each target analyte in filtered freshwater, and filtered and unfiltered effluent were determined by the referee laboratory. Background concentrations of the target analytes in reagent water were assumed to be zero. Spiking levels of each analyte in each matrix were determined according to background levels, the analytical range of the method, and water quality criteria.

The study was designed so that each participating laboratory would analyze sample pairs of each matrix of interest at concentrations that would span the analytical range of the method. Accordingly, the referee laboratory prepared a total of 11 sets of sample pairs for each participating laboratory in accordance with Results of the Interlaboratory Validation Study of EPA Method 1638 5Youden, W. J. and E. H. Steiner, 1975. Statistical Manual of the Association of Official Analytical Chemists, AOAC, 1111 North 19th Street, Suite 210, Arlington, VA 22209.

Draft  December 2000 3 ASTM procedures and Youden guidelines. 5 Samples were prepared as either duplicates or Youden pairs and distributed to the participating laboratories as blind samples ( e. g., the laboratories did not know the matrix or concentration of the analytes). The matrices and concentrations of each of the 11 sample pairs distributed to the participating laboratories are shown in Table 2 1.

The referee laboratory shipped 11 sample pairs ( 22 samples total) to each of 8 participating laboratories, for a total of 176 blind samples. The participating laboratories also were provided instructions concerning sample handling, analysis, and data reporting. To measure the recovery and precision of the analytical system, and to monitor matrix interferences, the laboratories were instructed to analyze matrix spike and matrix spike duplicate ( MS/ MSD) samples on specified field samples in each filtered and unfiltered matrix.

Table 2 1: Validation Study Samples Sent to Participating Laboratories Analyte Matrix Background Concentration ( µ g/ L) Expected Concentration ( µ g/ L) Total Pairs/ Lab Total Pairs/ Matrix Sb Filtered Freshwater 0.1241 0.1241 0.2041/ 0.2441 0.4041/ 0.5041 0.8041/ 1.0041 4 32 Filtered Effluent 0.9661 1.0000 1 8 Unfiltered Effluent 0.4066 10.0000 1 8 Reagent Water 0.0000 0 0.1000/ 0.1200 1.000 5.000 20.000 5 40 Cd Filtered Freshwater 0.0000 0 0.0400/ 0.0500 0.1200/ 0.1400 0.2500 4 32 Filtered Effluent 0.1080 0.3000 1 8 Unfiltered Effluent 0.1250 0.5000 1 8 Reagent Water 0.0000 0 0.0500/ 0.0600 0.1000 1.0000 10.0000 5 40 Cu Filtered Freshwater 1.0300 1.0300 1.5300/ 1.7300 2.5300/ 3.0300 4.5300/ 5.0300 4 32 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 2 1: Validation Study Samples Sent to Participating Laboratories Analyte Matrix Background Concentration ( µ g/ L) Expected Concentration ( µ g/ L) Total Pairs/ Lab Total Pairs/ Matrix Draft  December 2000 4 Filtered Effluent 13.8000 13.8000 1 8 Unfiltered Effluent 15.1000 15.1000 1 8 Reagent Water 0.0000 0 0.2000/ 0.2400 0.5000 2.0000 20.0000 5 40 Pb Filtered Freshwater 0.0128 0.0128 0.0528/ 0.0628 0.2000 0.3128/ 0.3628 4 32 Filtered Effluent 0.4585 0.5000 1 8 Unfiltered Effluent 1.0557 1.0557 1 8 Reagent Water 0.0000 0 0.0300/ 0.03600 0.1000 0.5000 5.0000 5 40 Ni Filtered Freshwater 0.3100 0.3100 1.6100/ 1.8100 3.3100/ 4.0100 6.0000 4 32 Filtered Effluent 2.6000 7.0000 1 8 Unfiltered Effluent 2.7100 8.0000 1 8 Reagent Water 0.0000 0 0.5000/ 0.6000 1.0000 10.0000 100.0000 5 40 Se Filtered Freshwater 0.3810 0.3810 0.9810/ 1.1810 1.9810/ 2.3810 4.0000 4 32 Filtered Effluent 0.3277 5.0000 1 8 Unfiltered Effluent 0.3440 6.0000 1 8 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 2 1: Validation Study Samples Sent to Participating Laboratories Analyte Matrix Background Concentration ( µ g/ L) Expected Concentration ( µ g/ L) Total Pairs/ Lab Total Pairs/ Matrix Draft  December 2000 5 Reagent Water 0.0000 0 1.0000/ 1.2000 5.0000 20.0000 100.0000 5 40 Ag Filtered Freshwater 0.0000 0 0.0700/ 0.0800 0.2000 0.3000/ 0.3600 4 32 Filtered Effluent 0.4780 0.4780 1 8 Unfiltered Effluent 2.8800 2.8800 1 8 Reagent Water 0.0000 0 0.2000/ 0.2400 0.1000 1.0000 10.0000 5 40 Tl Filtered Freshwater 0.0010 0.0010 0.0210/ 0.0240 0.0600 0.1010/ 0.1210 4 32 Filtered Effluent 0.0020 0.2000 1 8 Unfiltered Effluent 0.0020 0.9000 1 8 Reagent Water 0.0000 0 0.0400/ 0.0500 0.1000 0.5000 2.0000 5 40 Zn Filtered Freshwater 0.9743 0.9743 1.1043/ 1.3043 1.5000 1.7943/ 2.1943 4 32 Filtered Effluent 43.8250 43.8250 1 8 Unfiltered Effluent 48.0100 48.0100 1 8 Reagent Water 0.0000 0 2.0000/ 2.4000 0.5000 5.0000 50.0000 5 40 Results of the Interlaboratory Validation Study of EPA Method 1638 6The Sample Control Center ( SCC) is operated by DynCorp under EPA Contract No. 68 C 98 139. All SCC activities were performed under the direction and guidance of the EPA Analytical Methods Staff.

Draft  December 2000 6 To demonstrate the stability of samples throughout the study, the referee laboratory randomly selected and analyzed aliquots of each matrix type. Initial stability analyses were performed when samples were shipped to the participating laboratories and final stability analyses were performed 30  35 days following sample shipment. Results of the stability analyses were submitted to the Sample Control Center ( SCC) for assessment of instability or possible contamination. 6 2.3 Phase 3  Blind Sample and QC Sample Analyses The objective of Phase 3 was to evaluate the performance of Method 1638 in multiple laboratories. A secondary objective was to evaluate and, if appropriate, revise the QC acceptance criteria in the draft method.

Because the study was used to evaluate method performance under routine laboratory conditions, laboratories participating in Phase 3 were prohibited from performing multiple analyses to improve results. Laboratories, however, were permitted to implement corrective action and reanalyses for QC failures attributable to analyst error or to instrument failure.

Laboratories participating in Phase 3 were required to analyze each of the 22 blind samples sent by the referee laboratory under Phase 2. The laboratories also were required to perform all required Method 1638 QC analyses, including initial precision and recovery ( IPR), ongoing precision and recovery ( OPR), method blanks, calibration blanks, and matrix spike/ matrix spike duplicate ( MS/ MSD) pairs.

Each laboratory was required to prepare and analyze one MS and one MSD sample for filtered freshwater, filtered effluent, and unfiltered effluent for a total of three MS/ MSD sample pairs. Samples to be used for MS/ MSD analyses were identified by the referee laboratory on the sample bottles and sample tracking documents. Participating laboratories were instructed to spike aliquots of indicated MS/ MSD samples at 1 5 times the background concentration of the analytes determined by analysis of an unspiked aliquot of the sample.

Laboratories were required to submit sample results, raw data, run chronologies, chromatograms, example equations, and narrative discussions to EPA for review and validation.

Section 3 Study Management and Implementation The Study was designed and managed by EPA Office of Water's Analytical Methods Staff ( AMS), with participation by the Electric Power Research Institute ( EPRI). Day to day coordination of activities was performed by SCC. Phase 1 activities associated with determination of the MDL were performed by 10 laboratories. Phase 2 activities associated with collection, background determination, stability analyses, preparation, and distribution of samples were performed by Frontier Geosciences, Inc. ( the referee laboratory) operating under direction and guidance from SCC and EPRI. Phase 3 activities associated with analysis of blind sample pairs and associated QC samples were performed by eight participant laboratories operating either on a voluntary basis or under contract to EPA. The referee laboratory and eight participant laboratories are listed in Table 3 1. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 7 Table 3 1: Laboratories Participating in the Method 1638 Validation Study Battelle Marine Sciences Laboratory 1529 West Sequim Bay Road Sequim, WA 98382 360 681 3650 Commonwealth of Virginia Bureau of Analytical Services Division of Consolidated Lab Services 1 North 14th Street Richmond, VA 23219 804 786 7755 USEPA Region 10 Manchester Laboratory 7411 Beach Drive Port Orchard, WA 98366 360 871 8706 Hampton Roads Sanitation District 1432 Air Rail Avenue Virginia Beach, VA 23455 757 460 4203 University of Iowa State Hygienic Laboratory H. A. Wallace Building 900 East Grand Avenue Des Moines, IA 50319 515 281 5371 Southwest Research Institute 6220 Culebra Road San Antonio, TX 78238 5166 210 522 5428 University of Notre Dame Department of Civil Engineering & Geology 106 Cushing Notre Dame, IN 46556 219 631 9049 Texas A& M Department of Oceanography 100 Bizzell Eller Bldg., Room 403 College Station, TX 77843 3146 409 845 5137 Frontier Geosciences, Inc. ( referee lab) 414 Pontius North Seattle, WA 98109 206 622 6960 Note: The primary purpose of this study was to evaluate the performance of Method 1638. While the data submitted by these laboratories were assessed for this purpose, no attempt was made to assess laboratory performance. No endorsement of these laboratories is implied, nor should any be inferred. Laboratories have been assigned random numbers from 1 to 8 for purposes of reporting data in the tables or lists included in this report. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 8 The study was implemented as described in the February 1997 Study Plan with the following exceptions:

C EPA was able to obtain only eight laboratories based on the Phase 1 study instead of the minimum of nine laboratories recommended in the Study Plan. Of this, EPA funded participation of five laboratories, and three additional laboratories participated on a voluntary basis. This was considered to be a sufficient number to meet overall study objectives.

C Laboratories that voluntarily participated in Phase 3 of the study were encouraged but not required to participate in Phase 1 as well.

C The Study Plan recommended that MDLs be determined by analysis of at least seven replicates known to contain the analytes of interest at a concentration of 1 to 5 times the estimated MDL. This recommendation was included to ensure that the MDLs are not artificially high due to high spiking levels. Although some laboratories did not meet this specification, they did meet the requirements of the EPA MDL procedure given at 40 CFR 136, Appendix B.

C The referee laboratory did not collect or analyze field blanks with matrix samples. When collecting field samples for regulatory purposes, EPA believes it is important that field blanks be collected to rule out contamination during the collection procedure. However, EPA did not require field blank collection for this Study. The purpose of this study was to evaluate method performance rather than to characterize a field sample.

C The Study Plan called for each participant laboratory to analyze three pairs of reagent water samples and one pair each of filtered freshwater, filtered effluent, and unfiltered effluent. Funding provided by EPRI allowed inclusion of four additional blind sample pairs: three filtered freshwater and one reagent water. EPA also increased the number of samples sent to each participant laboratory by adding an additional reagent water sample pair.

C The stability analysis in Phase 2 covered the planned length ( 30 days) of Phase 3, but did not cover the actual length of Phase 3. Due to contract delays, laboratories 3, 6, and 7 analyzed Phase 3 samples after the final stability analysis was performed, but within the holding times for the samples.

C The referee laboratory did not prepare sufficient volume of unfiltered effluent to allow each participant laboratory to perform MS/ MSD analyses. In order to maintain the integrity of the study, the participant laboratories were directed to digest 30 mL aliquots rather than 100 mL aliquots for total recoverable metals. Because only a sub aliquot of the digested sample is injected into the instrument, this change was acceptable for the purposes of this study.

C The referee laboratory requested approval to run a single calibration for total and dissolved metals using HNO3/ HCl ( Draft Method 1638 specifies HNO3/ HCl and HNO3 for total recoverable and dissolved metals respectively). EPA approved this modification and requested that all participant laboratories prepare calibration standards, method blanks, other applicable QC samples, and both dissolved and total recoverable samples, with the appropriate acids at the appropriate concentrations using the total recoverable metals procedure. This involved the addition of nitric and hydrochloric acids to all samples for dissolved metal determinations.

C Following Phase 1, five participant laboratories requested permission to calibrate with linear regression instead of response factors. Because response factor calibration is statistically Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 9 equivalent to weighted linear regression forced through zero, EPA approved this calibration technique. Weighted linear regression with a non zero y intercept also was accepted; this approach can be considered equivalent to the response factor calibration technique because the instrument response is weighted in the same way. These alternate calibration approaches were allowed because ICP/ MS instruments typically utilize software with an option to calibrate with linear regression, but response factor calibration requires export of raw data from the instrument. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 10 Section 4 Data Reporting and Validation Data reports were submitted to SCC for review and validation. The reports included MDL study results ( Phase 1), background determination, sample analysis, and sample stability results ( Phase 2), and study data packages ( Phase 3). Data packages included sample tracking logs, results summaries, QC summaries, raw data, sample calculations, laboratory narratives, and electronic data reporting spreadsheets.

Seven of the eight participant laboratories submitted Phase 1 data packages. Laboratory 4 chose not to participate in the MDL study.

The referee laboratory submitted a complete data package describing all Phase 2 activities and results, including sample collection and preparation information, analytical results of background determinations, analytical results of post spiking sample concentrations, results from sample stability analyses, and copies of all hardcopy sample tracking documentation.

All eight participant laboratories submitted Phase 3 data packages. Results were submitted for all 176 samples distributed ( 22 sample results from each of 8 laboratories) yielding a 100% laboratory completion rate. Results also were submitted for most of the required QC analyses. The type and number of study samples analyzed and reported by each laboratory in Phase 3 are listed in Table 4 1. Laboratories also reported spike amounts, percent recoveries, and true values for QC samples. For those instances in which Study Plan requirements were not met, an explanation was provided or the situation resolved through discussions with the laboratory.

Table 4 1: Number and Type of Phase 3 Samples Analyzed by Participating Laboratories Lab Runs1 Blind Samples MS/ MSD QCS2 SRM3 IPR OPR Cal Ver Method Blanks Cal Blanks non zero CAL4/ Run 1 1 22 3/ 3 0 1 to 2 4 2 5 10 0 3 2 6 22 4/ 4 3 to 6 2 to 6 4 7 to 15 10 to 20 9 to 19 12 to 26 4 to 5 3 2 22 4/ 4 0 1 4 3 10 to 14 3 10 to 14 4 4 2 22 4/ 4 7 to 9 5 to 8 12 5 to 8 2 to 5 2 to 4 9 to 10 5 to 7 5 4 22 4/ 4 10 4 8 10 9 1 9 3 to 7 6 1 22 3/ 0 0 2 6 0 0 0 4 6 7 1 22 3/ 3 0 3 to 6 4 3 7 3 6 3 8 1 22 5/ 5 3 1 4 3 7 3 7 3 1 " Run" is defined as a group of samples associated with a calibration. 2 Quality control samples ( QCSs) are required by Method 1638, but were not required for this study. 3 SRMs are not required by Method 1638 but at least one analysis was required for this study. 4 A minimum of three non zero calibration standards ( CAL) are required by Method 1638.

Data were reviewed against the requirements of the Study Plan and against the specifications in Method 1638. Data completeness was verified by ensuring all required data were present, including results of all required tests, sample lists, run chronologies, summaries of analytical results, raw data, and copies of laboratory notebook entries. Data verification was performed by comparing each data element to the requirements of the Study Plan. This included verification that: reagent water, freshwater, and effluent Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 11 samples were analyzed as appropriate; proper spike levels were used in the MDL studies and QC analyses; the analytical system was properly calibrated; and the MDLs were calculated in accordance with the MDL procedure at 40 CFR 136, Appendix B.

4.1 Phase 1 Phase 1 results were used to pre qualify laboratories for participation in Phase 3 and to revise draft Method 1638 MDLs ( Section 6.1). Based on the SCC data review and discussions with the laboratories to resolve discrepancies, Phase 1 data from 7 of the 10 laboratories were considered to be of acceptable quality.

Three laboratories did not submit acceptable Phase 1 data. One laboratory submitted level of quantitation ( LOQ) results instead of an MDL study and used only one calibration point instead of the required three. A second laboratory was unable to meet draft method MDLs for six of the nine analytes and reported antimony and lead contamination in their blanks. The third laboratory was unable to meet draft method MDLs for seven of the nine analytes, and method blanks were greater than the MDL for all nine analytes, indicating laboratory contamination.

All MDLs reported were determined according to the procedure at 40 CFR part 136, Appendix B. The Study Plan recommended that MDLs determined in Phase 1 be within a factor of five of the level spiked so that the determined MDLs would not be artificially high due to high spiking levels. Although some MDLs did not meet this objective, they did meet all requirements of the EPA MDL procedure given at 40 CFR 136, Appendix B. Therefore, all data were used to evaluate the MDLs in Method 1638. Results for Phase 1 are presented in Section 5.1.

As part of Phase 1, laboratories also were required to analyze at least one method blank. All laboratories analyzed one method blank except Laboratory 8, which analyzed two method blanks. Phase 1 method blank results are presented in Table 5 1.

4.2 Phase 2 Based on data review and discussions with the referee laboratory to resolve discrepancies, all Phase 2 data were considered to be of acceptable quality. Phase 2 results were used to determine spiking levels and sample stability. Phase 2 results also were used as the basis for determining percent recoveries in the Phase 3 data.

During Phase 2, the referee laboratory determined the mass to charge ratios ( m/ z) that it determined should be used for quantitation based on the results of individual analytical runs. As a result, some of the data reported were not quantified using m/ z's recommended in Method 1638. Specifically, in the stability study, the laboratory reported all data using 114Cd, 121Sb, 65Cu, and 68Zn. EPA believes that there is no adverse impact to this use of alternate m/ z's because the m/ z's in Method 1638 are recommended but not required.

4.3 Phase 3 Data submitted for Phase 3 met study and method requirements. Sections 4.3.1 through 4.3.8 detail deviations from these requirements. Results of the Interlaboratory Validation Study of EPA Method 1638 7EPA Guide to Method Flexibility and Approval of EPA Water Methods, EPA 821 D 96 004, December 1996.

Draft  December 2000 12 4.3.1 Calibration Verification Samples Method 1638 requires the laboratory to verify instrument calibration immediately following calibration and after every ten samples. Calibration is verified by analysis of the mid point calibration standard. Several laboratories did not analyze the mid point standard, but did analyze a standard in the middle of their calibration range. Other laboratories analyzed calibration samples that were not in the middle of the calibration range, or were greater than the calibration range. All calibration verification samples that were within the laboratory calibration ranges were included in the assessment of the QC acceptance criteria for the method.

Laboratory 6 did not analyze calibration verification samples, but instead analyzed SRMs ( SLRS 2) at the beginning and end of each analytical run. Analytical results for SRMs can be used to verify calibration, so long as analyte concentrations are in the calibration range. The analytical results for SRMs showed acceptable recoveries and, therefore, calibration was considered verified. Results for the SRMs were not used for development of calibration verification QC acceptance criteria. The results are presented in Table 5 6.

4.3.2 Initial Precision and Recovery Samples Draft Method 1638 requires laboratories to spike each initial precision and recovery ( IPR) sample with each analyte at a concentration two to three times the ML for that analyte. EPA intends to revise Method 1638 to specify that the concentration of IPR sample aliquots be at one to five times the ML in order to make the method consistent with EPA's Guide to Method Flexibility and Approval of EPA Water Methods7 ( the " Streamlining Guide"), which was published after the release of draft Method 1638. All IPR samples spiked at the draft method ML or greater were included in EPA's assessment of the IPR QC acceptance criteria, even if the levels spiked were higher than specified in the method.

Laboratories 4 and 6 submitted IPR results for more than the method specified minimum of four replicates. Laboratory 4 analyzed a total of sixteen IPR samples. Laboratory 6 analyzed six IPR samples. These two laboratories also analyzed their IPR samples after the Phase 3 samples. The data were considered acceptable for use in evaluating method performance because the data were collected in the same way as IPR data run prior to sample analyses were collected. Results for IPR samples are provided in Appendix B, Table 4.

4.3.3 Ongoing Precision and Recovery Samples Draft Method 1638 requires laboratories to spike each OPR sample at a level two to three times the ML for each analyte. As with the IPR requirements, EPA intends to revise Method 1638 to specify that the concentration of OPR sample aliquots be one to five times the ML in order to make the method consistent with the Streamlining Guide. All OPR samples spiked at the draft method ML or greater were included in EPA's assessment of the OPR QC acceptance criteria, even if the levels spiked were higher than specified in the method. Laboratory 6 did not analyze OPR samples. OPR sample results are provided in Appendix B, Table 4. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 13 4.3.4 Blanks Method 1638 requires laboratories to analyze 1) method blanks with every sample batch, and 2) calibration blanks following calibration verification. The concentration of each target analyte in the blanks must be below the MDL for that analyte. Alternatively, if three or more blanks are analyzed to characterize the nature of a blank, the average concentration plus two standard deviations must be less than the regulatory compliance limit. Negative values are common when using ICP/ MS to analyze samples that have concentrations below the MDL. Although not specified in the draft method, it is widely understood that extreme negative values can indicate signs of instrument drift or other problems that can result in negative bias. Further revisions of Method 1638 will address this issue. For the purposes of this study, SCC compared the absolute value of blank results to the revised MDLs.

Laboratory 1 did not analyze calibration blanks and Laboratory 6 did not analyze method blanks. Results from these laboratories were assessed for possible contamination by examining QC sample results ( e. g., calibration blanks, IPR/ OPR, calibration verification, SRMs). Quality control sample results from these laboratories met method specifications, suggesting no evidence of a high bias that would be observed if contamination were present in the laboratories. Similarly, a comparison of field sample results reported by these laboratories showed no evidence of high bias compared to results reported by other laboratories. Based on these factors, EPA considered data reported by these laboratories to be acceptable for study purposes unless otherwise noted in this report. Blank results were assessed by comparison to the revised MDLs ( determined using Phase 1 data). Results of the comparison are given in Sections 5.3.6 and 5.3.7. Blank results are listed in Appendix B, Table 5.

4.3.5 Matrix Spike and Matrix Spike Duplicate Samples The referee laboratory identified samples to be used for MS/ MSD analysis on sample labels and traffic reports. Five of the participant laboratories analyzed additional MS/ MSD samples. Laboratories 2, 3, 4, and 5 each analyzed an additional set of filtered freshwater MS/ MSD samples. Laboratory 8 analyzed a set of MS/ MSD reagent water samples. Laboratory 6 performed MS analyses on the samples identified but did not analyze corresponding MSD samples. When revising Method 1638 to reflect study findings, EPA intends to revisit the language contained in Section 9.3 of the method to ensure that laboratories clearly understand the requirement to analyze both MS and MSD samples.

Laboratories were directed to spike MS/ MSD samples at one to five times the ML or one to five times the background concentration in the sample, whichever was greater. Several laboratories did not meet this spiking requirement. MS/ MSD samples spiked at the draft method ML or greater were included in EPA's assessment of the MS/ MSD QC acceptance criteria.

Results for MS/ MSD samples are provided in Appendix B, Table 3 with associated spiking levels.

4.3.6 Calibration All laboratories complied with method requirements for instrument calibration using a calibration blank and at least three non zero standards. Method 1638 also directs laboratories to calibrate their instruments using response factors ( height or area at the analyte m/ z divided by the analyte concentration).

Upon request from the participant laboratories, two changes to the calibration procedure were approved for this study: C Due to the variety of linear dynamic ranges ( LDR) across instruments and because the sensitivity of certain instruments could be adversely affected by injection of high concentration calibration Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 14 solutions, the laboratories were instructed to prepare the high calibration standard as high as was practical. C Many ICP MS instruments use software that allows for weighted linear regression but not response factor calibration. EPA agreed that laboratories could calibrate using weighted linear regression.

Laboratory 3 used a response factor calibration as specified in the method. Laboratories 4 and 6 submitted data calculated using unweighted linear regression. All other laboratories used weighted linear regression calibration. Although not specifically approved, the data generated using unweighted linear regression also were considered valid for use in this study ( this calibration technique is widely practiced as the industry standard for metals determinations in environmental samples).

Draft Method 1638 also requires that the lowest non zero standard be at the minimum level ( ML), and the high standard be near the upper end of the linear dynamic range. Several laboratories did not consistently use a low standard at the minimum levels, however, most laboratories encompassed the ML by using one standard below the ML and a mid level standard above the ML. Seven laboratories analyzed field and QC samples with concentrations exceeding those in the laboratory's high standard. Sample results outside a laboratory's calibration range ( i. e., below the lowest calibration standard or above the highest calibration standard) were not used to assess the performance of Method 1638.

4.3.7 Standard Reference Material Analyses Each participant laboratory received and analyzed the National Institute of Science and Technology ( NIST) standard reference material ( SRM) 1643d. Laboratories 1 and 7 analyzed an additional SRM ( SLRS 4) from the Canadian National Research Council ( NRC), containing six of the nine target analytes ( excluding silver, selenium, and thallium) at lower levels than 1643d. The cadmium concentration in SLRS 4 is below the draft and the revised method MDL. Percent recoveries of SRM samples analyzed by the participant laboratories are presented in Table 5 12.

4.3.8 Additional Deviations Additional deviations from study requirements that are not related to the specific QC detailed in Sections 4.3.1 through 4.3.7 are listed below. In most cases, the deviations did not warrant data removal.

C Laboratory 1 prepared two OPRs and analyzed each OPR multiple times. Only the first analytical result for each OPR was used to develop OPR QC acceptance criteria.

C Laboratory 2 analyzed an OPR with a 1050% selenium recovery. The laboratory suspected the result was an anomaly and immediately repeated the analysis. Laboratory 2 prepared and analyzed eight additional OPR samples and reported recoveries for these OPR sample analyses ranging from 84 127 % recovery. Because eight of the nine OPR sample results were within the draft method specifications, EPA agreed with the laboratory's assessment that the data were an anomaly. EPA did not use the elevated selenium recovery concentration to assess method performance.

C Method 1638 requires that a method blank be prepared and analyzed with each analytical batch. Laboratory 3 analyzed three method blanks under the first calibration and no method blanks under the second calibration. All three method blanks were analyzed during the first of eight batches instead of one method blank per batch. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 15 ( ) ( ) ( ) Pb Pb Pb Pb total = + + 0 241 0 221 0 524 206 207 208 . * . * . * C Laboratory 4 analyzed all samples twice. The first run was used to screen samples for concentration. Although the laboratories were instructed not to repeatedly analyze samples to improve performance, they were not precluded from implementing such a screening approach. ( To the contrary, such an approach is often used to ensure that elevated sample concentrations do not contaminate clean equipment and to determine spiking levels). Therefore EPA chose to ignore the screening data and consider results from only the second run for all analytes except dissolved silver. The laboratory determined that spike recoveries for dissolved silver were not acceptable on the second day of analysis based on analysis of prepared standards, and thus reported dissolved silver and associated QC samples from the first day. Additional details on problems associated with silver recoveries are presented in Section 5.4.

C In Laboratory 5, sample preparation and analysis was not performed in a clean room or clean area. The laboratory indicated that samples high in target analytes were analyzed at the same site and on the same instrument on a routine basis. Not surprisingly, Laboratory 5 reported total recoverable OPR samples with elevated recoveries for copper ( 510 %) and lead ( 514 %). The laboratory attributed the elevated recoveries to possible contamination, noting that they frequently analyzed samples high in copper and lead. The OPR samples for copper and lead were not used for development of QC specifications for the method.

C Laboratory 5 analyzed the MS/ MSD for sample 46534 three times; once undiluted, once diluted 2X, and once diluted 10X. Copper and antimony spike recoveries were close to zero for both the undiluted and 2X dilution samples, and the laboratory reported the results for the 10X dilution. The laboratory stated that there may have been a matrix effect causing the poor recoveries. EPA compared background results for the undiluted sample to results reported by the other laboratories and found that there were no indications of matrix effects. Because of the inability of the laboratory to discern the matrix effects, EPA decided not to include the copper and antimony MS/ MSD results from this sample in the assessment of method performance.

C Laboratory 6 did not perform the recommended correction equation to account for the variability of lead isotopes. The laboratory reported separate concentrations for 206Pb, 207Pb, and 208Pb. EPA applied the following correction equation to the laboratory's data to account for the natural abundance of the lead isotopes:

C Laboratory 7 submitted results for each analyte calculated using several different internal standards. Only one internal standard is recommended in the method. During data review, EPA chose the most appropriate method specified internal standard and re calculated the results.

C Method blank and OPR sample results submitted by Laboratory 8 exhibited zinc contamination. The laboratory was unsure of the source of contamination. The method blanks, OPRs, and associated field samples are footnoted in this report. The QC samples were not used for development of OPR QC acceptance criteria.

All data deemed inappropriate for development of QC acceptance criteria are identified in Section 5. In addition, data that were not used are included as footnoted sample results in Appendix B. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 16 Section 5 Results Results submitted for Phase 1 are discussed in Section 5.1. These results were used to assess laboratory capability and to either validate the MDL's specified in the draft method or develop revised MDLs when the draft method MDL was not supported by study results.

Results submitted for Phase 2 are presented in Section 5.2 and in Appendix B, Table 1. These results were used to establish background and expected concentrations for each study sample and to assess sample stability for each target analyte.

Phase 3 results are presented in Section 5.3 and in Appendix B, Table 2. These results were used to evaluate method performance in real world matrices and develop performance criteria for Method 1638.

5.1 Phase 1 Results All laboratories followed the 40 CFR 136, Appendix B MDL procedure for Phase 1 MDL determinations. Results of the Phase 1 MDL and method blank assessments are given in Table 5 1. Laboratory 6 analyzed 10 replicates to determine their MDLs; all other laboratories analyzed the minimum requirement of 7 replicates. MDLs were calculated using the appropriate Student's t value to reflect the actual number of replicates ( n) used. These MDLs were evaluated and used to either confirm the draft method MDLs or to calculate a revised MDL as appropriate.

Absolute values of method blanks reported during Phase 1 were evaluated based on these confirmed or revised MDLs. Of the 71 Phase 1 method blank results reported, more than 80% were below the confirmed or revised MDLs. Laboratory 4 agreed to participate in the study after the completion of Phase 1 and did not participate in Phase 1 of the study. 17 Table 5 1: Phase 1, MDL and Method Blank Results Analyte Lab Spiking Concentration ( µ g/ L) MDL Results ( µ g/ L) Method Blank Results ( µ g/ L) 1 2 3 4 5 6 7 8 9 10 Mean ( µ g/ L) s MDL ( µ g/ L)

Antimony 1 0.02 0.014 0.017 0.011 0.014 0.022 0.018 0.017    0.016 0.003 0.011 0.103 2 0.03 0.028 0.037 0.037 0.031 0.027 0.040 0.032    0.033 0.005 0.016 0.004 3 0.05 0.033 0.033 0.027 0.027 0.033 0.029 0.027    0.030 0.003 0.009  0.016 5 0.02 0.019 0.017 0.015 0.018 0.020 0.017 0.017    0.018 0.002 0.005 0.014 6 0.051 0.048 0.043 0.041 0.046 0.039 0.038 0.043 0.031 0.044 0.037 0.041 0.005 0.014 0.004 7 0.01 0.011 0.007 0.008 0.009 0.010 0.005 0.007    0.008 0.002 0.007  0.005 8 0.1 0.089 0.063 0.057 0.051 0.043 0.046 0.056    0.058 0.015 0.048  0.081  0.032 Cadmium 1 0.02 0.031 0.035 0.028 0.035 0.036 0.029 0.025    0.031 0.004 0.013 0.159 2 0.3 0.311 0.327 0.341 0.323 0.291 0.369 0.319    0.326 0.024 0.077 0.027 3 0.025 0.021 0.017 0.020 0.022 0.025 0.020 0.024    0.021 0.003 0.008  0.002 5 0.1 0.097 0.087 0.093 0.082 0.092 0.100 0.082    0.090 0.007 0.022 0.018 6 0.041 0.064 0.041 0.053 0.045 0.035 0.043 0.043 0.032 0.048 0.054 0.046 0.009 0.026 0.006 7 0.05 0.020 0.018 0.021 0.023 0.019 0.014 0.020    0.019 0.003 0.009  0.033 8 0.05 0.013 0.011 0.013 0.008 0.014 0.013 0.024    0.014 0.005 0.016  0.040  0.025 Copper 1 0.05 0.039 0.048 0.047 0.047 0.046 0.038 0.058    0.046 0.007 0.021 0.002 2 0.3 0.361 0.342 0.374 0.346 0.342 0.349 0.414    0.361 0.026 0.081  0.052 3 0.025 0.036 0.032 0.025 0.029 0.030 0.030 0.033    0.031 0.003 0.011  0.025 5 0.2 0.179 0.195 0.195 0.196 0.194 0.188 0.200    0.192 0.007 0.022 0.176 6 1.016 1.034 1.013 1.016 0.906 0.966 1.035 1.063 1.003 1.060 1.028 1.013 0.047 0.132 0.094 7 0.1 0.089 0.084 0.085 0.085 0.084 0.086 0.081    0.085 0.003 0.008  0.006 8 0.05 0.055 0.050 0.043 0.054 0.047 0.048 0.054    0.050 0.005 0.014 0.027 0.018 Lead 1 0.02 0.023 0.022 0.024 0.019 0.022 0.024 0.021    0.022 0.002 0.005 0.009 2 0.05 0.067 0.061 0.070 0.065 0.065 0.064 0.065    0.065 0.003 0.009 0.100 3 0.025 0.021 0.021 0.019 0.021 0.020 0.021 0.022    0.021 0.001 0.003 0.000 Table 5 1: Phase 1, MDL and Method Blank Results Analyte Lab Spiking Concentration ( µ g/ L) MDL Results ( µ g/ L) Method Blank Results ( µ g/ L) 1 2 3 4 5 6 7 8 9 10 Mean ( µ g/ L) s MDL ( µ g/ L)

18 5 0.05 0.035 0.040 0.044 0.043 0.035 0.043 0.041    0.040 0.004 0.012 0.019 6 0.051 0.048 0.048 0.044 0.045 0.038 0.044 0.042 0.042 0.041 0.040 0.043 0.003 0.009 0.007 7 0.025 0.026 0.025 0.025 0.025 0.026 0.026 0.026    0.026 0.001 0.002 0.002 8 0.1 0.087 0.092 0.095 0.098 0.098 0.098 0.097    0.095 0.004 0.013  0.005 0.000 Nickel 1 0.1 0.084 0.084 0.094 0.091 0.065 0.069 0.092    0.083 0.011 0.036 0.000 2 0.1 0.233 0.215 0.208 0.224 0.211 0.203 0.205    0.214 0.011 0.034 0.015 3 0.025 0.022 0.022 0.027 0.023 0.029 0.026 0.022    0.024 0.003 0.009  0.005 5 0.5 0.355 0.370 0.414 0.436 0.383 0.331 0.376    0.381 0.035 0.111 1.130 6 1.036 0.976 0.932 0.935 0.986 0.992 1.014 1.036 1.003 1.009 1.025 0.991 0.035 0.099 0.110 7 0.5 0.475 0.474 0.471 0.479 0.475 0.463 0.474    0.473 0.005 0.015 0.010 8 0.05 0.034 0.038 0.037 0.042 0.035 0.039 0.041    0.038 0.003 0.010 0.007 0.003 Selenium 1 0.5 0.310 0.516 0.503 0.578 0.968 0.545 0.403    0.546 0.207 0.652 0.250 2 No data submitted by laboratory 3 1 0.703 0.805 0.821 0.888 0.956 0.779 0.768    0.817 0.083 0.261  0.146 5 1 0.796 0.696 0.777 0.949 0.958 0.622 0.884    0.812 0.127 0.398 0.885 6 2.499 2.237 2.143 1.882 2.060 1.432 1.495 1.589 2.133 2.227 1.652 1.885 0.316 0.891 0.710 7 2.5 2.401 2.417 2.282 2.333 2.369 2.313 2.336    2.350 0.048 0.151  0.027 8 0.5 0.466 0.617 0.430 0.467 0.522 0.605 0.601    0.530 0.078 0.245  0.027 0.020 Silver 1 0.02 0.025 0.027 0.032 0.028 0.024 0.026 0.027    0.027 0.003 0.008 0.011 2 0.05 0.065 0.056 0.067 0.051 0.062 0.059 0.052    0.059 0.006 0.019 0.018 3 0.05 0.019 0.019 0.014 0.022 0.018 0.017 0.020    0.019 0.002 0.008  0.022 5 0.02 0.010 0.013 0.011 0.008 0.007 0.010 0.011    0.010 0.002 0.006 0.023 6 0.091 0.098 0.087 0.081 0.067 0.089 0.076 0.079 0.070 0.077 0.080 0.080 0.009 0.026 0.019 7 0.05 0.054 0.050 0.051 0.052 0.051 0.048 0.049    0.051 0.002 0.006 0.002 Table 5 1: Phase 1, MDL and Method Blank Results Analyte Lab Spiking Concentration ( µ g/ L) MDL Results ( µ g/ L) Method Blank Results ( µ g/ L) 1 2 3 4 5 6 7 8 9 10 Mean ( µ g/ L) s MDL ( µ g/ L)

19 8 0.1 0.095 0.106 0.110 0.110 0.113 0.116 0.110    0.108 0.007 0.021 0.024 0.017 Thallium 1 0.02 0.025 0.024 0.024 0.023 0.023 0.023 0.021    0.023 0.001 0.004 0.006 2 0.02 0.017 0.018 0.018 0.028 0.026 0.026 0.026    0.023 0.005 0.015  0.019 3 0.005 0.003 0.003 0.003 0.003 0.003 0.003 0.003    0.003 0.000 0.001  0.002 5 0.02 0.024 0.018 0.019 0.019 0.020 0.020 0.022    0.020 0.002 0.006 0.010 6 0.051 0.042 0.045 0.042 0.042 0.045 0.044 0.042 0.040 0.042 0.042 0.043 0.002 0.005 0.001 7 0.01 0.010 0.010 0.011 0.011 0.011 0.010 0.010    0.010 0.000 0.001 0.000 8 0.05 0.040 0.040 0.040 0.038 0.041 0.042 0.042    0.040 0.001 0.004  0.008  0.004 Zinc 1 0.2 0.124 0.139 0.155 0.154 0.121 0.172 0.149    0.145 0.018 0.057 0.000 2 0.5 0.548 0.521 0.527 0.510 0.510 0.580 0.533    0.533 0.025 0.078 0.042 3 0.1 0.100 0.108 0.103 0.114 0.154 0.145 0.154    0.125 0.024 0.077  0.040 5 0.5 0.935 0.951 0.976 0.998 0.981 0.916 1.190    0.992 0.092 0.288 0.544 6 1.026 1.106 1.075 1.031 1.071 1.070 1.005 1.199 1.116 1.052 1.150 1.087 0.057 0.161 0.096 7 0.25 0.233 0.218 0.221 0.228 0.248 0.216 0.249    0.231 0.014 0.043  0.017 8 0.5 0.523 0.527 0.557 0.530 0.544 0.538 0.494    0.530 0.020 0.062 0.244 0.207 20 5.2 Phase 2 Results 5.2.1 Background Concentrations Background concentrations of the target analytes in the freshwater and effluent matrices were determined by the referee laboratory. The background concentration of the reagent water was assumed to be zero. The background concentrations were used to determine appropriate spiking levels for each target analyte in the blind samples distributed to the participating laboratories. Background concentrations are listed in Table 2 1.

5.2.2 Stability Analyses Aliquots from each batch of filtered and unfiltered samples were analyzed at the beginning and end of the 30 to 35 day stability test period, the expected duration of Phase 3. Results were submitted with full QC data to SCC for assessment of instability or possible contamination. Sample stability was assessed by comparing analytical results against the expected concentration. Mean percent recoveries for both initial analyses and final analyses were based on the expected analyte concentrations, and are presented in Appendix B, Table 1. Relative percent differences ( RPD) of mean percent recoveries were used to assess analyte concentration stability during Phase 3 of the study.

Stability could not be quantitatively assessed for samples having expected analyte concentrations below the MLs determined in Phase 1 ( Table 6 1). These samples are flagged in Appendix B, Table 1, and include ( 1) unspiked reagent water samples, ( 2) many of the Youden pairs that EPRI included in the study, and ( 3) one freshwater pair for antimony. EPA did, however, verify that these samples remained at or near this threshold over the 30 to 35 day stability test period. All but three of the low concentration sample pairs provided by EPRI were consistently below the ML. The three remaining pairs closely bracketed the ML. For example, antimony was initially reported at the ML ( 0.20 ug/ L) in a freshwater sample and slightly below the ML ( 0.17 ug/ L) for the final stability analysis. The expected concentration of antimony was reported to be at the ML ( 0.20).

Of the 117 non zero samples assessed for stability, 32 were removed from the assessment because the expected concentrations were below the revised method MLs. Of the remaining 85 samples, only four indicated possible instability.

C Reagent Water Pair 2 ( silver)  The RPD between silver measurements at the beginning and end of the stability period was 25.4%. The expected concentration of this sample pair was at the method ML for silver ( 0.1 µ g/ L). C Freshwater Pair  High ( silver)  The RPD between silver measurements was 121%. Final stability assessment yielded recovery of silver at less than a third of the expected and initial analyses concentrations. C Freshwater Pair  Low ( silver)  The RPD between silver measurements was 134%. Final stability assessment yielded recovery of silver at less than a third of the expected and initial analyses concentrations. C Unfiltered Effluent Pair ( silver)  Initial stability assessment yielded 52% recovery and the final stability assessment yielded 53% recovery. The RPD between silver measurements was 3% and the silver concentration was considered stable for the study period.

For all samples in which analyte concentrations were consistently reported above the ML, EPA determined that concentrations remained sufficiently stable during Phase 3 of the study. Results of stability analyses and assessment are shown in Table 1 of Appendix B. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 21 5.3 Phase 3 Results 5.3.1 Outlier Screening Sample results were screened for outliers in accordance with laboratory ranking and individual point procedures described by AOAC International and ASTM D 2777 96. The laboratories were ranked and screened according to Youden's test for outlying laboratories to identify laboratories with significantly higher or lower results than the majority of laboratories. For each analyte and sample type ( analyte/ matrix/ concentration), laboratories were ranked according to the distance between the analyte concentration determined by that laboratory and the mean concentration over all laboratories for the corresponding sample type and analyte. One of the eight Phase 3 data packages was rejected for each analyte following application of the Youden laboratory ranking test at the 5 percent significance level leaving 7 full datasets for each analyte for determination of method performance. Laboratory data packages that were removed for each analyte are listed in Table 5 2.

Table 5 2: Youden Outlier Laboratories Analyte Outlier Laboratory Antimony Laboratory 1 Cadmium Laboratory 6 Copper Laboratory 1 Lead Laboratory 1 Nickel Laboratory 2 Selenium Laboratory 6 Silver Laboratory 4 Thallium Laboratory 7 Zinc Laboratory 5 After identifying the Youden outlying laboratories, the data were screened for outliers using the statistical procedures attributed to Grubbs in the AOAC and ASTM procedures. This screening was conducted separately for: 1) the development of the QC acceptance criteria and 2) the assessment of method performance. For development of QC acceptance criteria, an objective was to use as much data as possible. All field and sample results that were above the draft method ML were used in the development of QC acceptance criteria. Therefore, results that were below the draft method ML were removed from the data set prior to applying the Grubbs outlier test. For assessment of method performance, all results that were above the revised method ML ( see Table 6 1) were used. This required a separate application of the Grubbs outlier test prior to conducting the method performance assessment presented in Section 7.

The Phase 3 field sample ( excluding Youden pairs), IPR/ OPR, and calibration verification results were screened for outliers using Grubbs test for outlying observations. The Grubbs outlier test allows for identification and removal of up to 10 percent of the samples for each matrix/ concentration/ analyte combination. Because there were fewer than 10 results for any given combination of method/ concentration/ analyte in the MS/ MSD and Youden pair samples, application of the Grubbs test to these samples could Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 22 not be performed because removal of any sample would violate the 10% removal limit specified for the Grubbs test. However, two results from Youden pairs were removed due to exceedingly high recoveries ( 3000% for sample 47292 Cd, and 1000% for sample 47245 Cu). Results remaining after removal of the Youden outlying laboratory, the Grubbs outliers, and the two Youden pair outliers were used for development of QC acceptance criteria.

The percentages of sample results that were rejected as outliers from the 7 full data sets for each analyte are listed in Table 5 3. Rejected outlying results are identified in Appendix B, Tables 2 and 4.

Table 5 3. Percentage of Sample Results Rejected as Grubbs Outliers Analyte Phase 3 Field (%) Precision and Recovery (%) Calibration Verification (%) Method Performance Precision and Recovery (%)

Sb 0 7 2 6 Cd 0 1 0 2 Cu 4 5 8 6 Pb 6 3 0 1 Ni 3 2 0 2 Se 0 1 6 1 Ag 0 0 0 0 Tl 2 1 0 1 Zn 1 2 0 3 5.3.2 Calibration Linearity Method 1638 stipulates that calibration is performed using response factors. For this study, both weighted and unweighted linear regression also were accepted ( see Section 3 for more information). EPA intends to revise Method 1638 to recommend use of response factor or weighted linear regression calibrations, allowing unweighted linear regression as an acceptable calibration technique.

Method 1638 requires each laboratory to calibrate the instrument with three or more non zero calibration standards. All laboratories followed this requirement. Five of the eight laboratories used weighted linear regression with a non zero y intercept. Of the remaining three laboratories, Laboratories 4 and 6 used unweighted linear regression, and Laboratory 3 used response factors. Calibration data were pooled for development of QC acceptance criteria and method performance evaluation regardless of calibration technique.

For response factor ( RF) calibration, the laboratory computes 1) the RF for each calibration point, 2) the mean response factor ( RFm), and 3) the relative standard deviation ( RSD) of the response factors. Method 1638 specifies a maximum criterion of 20 percent RSD of the RFs for each calibration run. Results Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 23 submitted by Laboratory 3 ( the only laboratory to calibrate using response factors) are shown in Table 5 4. The RSDs of all mean RFs were well below the maximum criteria of 20 percent.

Table 5 4. Laboratory 3 Calibration Results Analyte RFm s RSD Antimony 1.73 0.03 1.82 1.75 0.06 3.52 Cadmium 1.97 0.05 2.75 Copper 8.30 0.51 6.18 8.25 0.73 8.90 Lead 12.12 0.24 1.96 12.08 0.59 4.90 Nickel 3.52 0.12 3.28 3.53 0.09 2.66 Selenium 0.07 0.00 1.68 Silver 4.05 0.13 3.15 Thallium 8.96 0.21 2.38 Zinc 1.93 0.06 2.88 2.01 0.12 6.03 For weighted and unweighted linear regression, the laboratory calculates 1) the slope, 2) the y intercept, and 3) the correlation coefficient ( R2). EPA assessed the data relative to a lower limit of 0.995 for the correlation coefficient and set upper intercept limits at the MDLs. For all labs that used weighted and unweighted linear regression, reported correlation coefficients were always greater than 0.995, except for Laboratory 1. Laboratory 1 reported lower correlation coefficients for selenium and antimony, however, these correlation coefficients were above 0.990 and all data were considered acceptable for the study. All y intercepts were less than the MDLs with the exception of one result for lead. Calibration linearity was considered acceptable for each lab for the purposes of the study.

In order to evaluate method performance using a weighted linear regression, EPA re calculated calibrations using instrument response data submitted by all laboratories except Laboratory 2. Laboratory 2 did not submit raw instrument responses and was unable to provide them upon request.

It is to be expected that correlation coefficients using weighted linear regression would be lower than coefficients using unweighted linear regression because of the effect of equal weighting of all points in the weighted approach. Of the 67 weighted correlation coefficients calculated by EPA, 70 percent were greater than 0.995. The lowest correlation coefficient was 0.874 for lead. Lead most frequently had a correlation coefficient below 0.995 ( 6 percent of the total correlation coefficients). Results of the weighted linear regression assessment are shown in Table 5 5. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 24 Table 5 5. Weighted Linear Regression Results Analyte Lab Slope Intercept R2 Antimony 1 1.49  0.000018 0.986 2 Data not available 3 1.75  0.000028 1.000 1.77  0.000037 0.999 4 0.22 0.000033 0.992 5 0.18 0.000030 0.996 0.17 0.000036 0.997 6 Youden outlying laboratory 7 0.39  0.001834 1.000 8 0.89  0.000070 1.000 Cadmium 1 0.62  0.000006 0.990 2 Data not available 3 1.94 0.000054 1.000 4 0.09 0.000034 0.988 5 Youden outlying laboratory 6 0.08 0.000007 1.000 7 0.67  0.003960 1.000 8 0.44  0.000017 1.000 Copper 1 Youden outlying laboratory 2 Data not available 3 8.62  0.000511 0.999 8.71  0.000727 0.999 4 1.64 0.002584 0.987 5 0.39 0.000365 0.986 0.39 0.000334 0.996 6 0.58  0.002473 0.999 7 0.39  0.006303 1.000 8 1.12  0.000050 1.000 Analyte Lab Slope Intercept R2 Lead 1 Youden outlying laboratory 2 Data not available 3 12.27  0.000253 1.000 12.34  0.000415 0.998 4 0.77 0.000385 0.991 5 1.23 0.000067 0.975 1.23  0.000112 0.981 6 0.62  0.000915 0.874 7 1.68  0.015948 1.000 8 5.95 0.000048 0.999 Nickel 1 0.74 0.000043 0.992 2 Youden outlying laboratory 3 3.52 0.000007 0.999 3.55  0.000033 0.999 4 0.22 0.000129 0.989 5 0.17 0.000175 0.998 0.17  0.000153 1.000 6 0.26  0.000032 1.000 7 0.16  0.001399 1.000 8 0.56  0.000036 1.000 Selenium 1 0.03 0.000067 0.985 2 Data not available 3 0.07 0.000007 1.000 4 0.07 0.000156 0.984 5 0.01 0.000140 0.995 0.01 0.000123 0.988 6 Youden outlying laboratory 7 0.01  0.000713 1.000 8 0.04  0.000045 1.000 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 25 Table 5 5. Weighted Linear Regression Results Analyte Lab Slope Intercept R2 Silver 1 2.54  0.000050 0.992 2 Data not available 3 4.13  0.000126 1.000 4 Youden outlying laboratory 5 0.41 0.000069 0.998 0.41  0.000009 0.997 6 0.34 0.003306 0.995 7 0.67  0.003960 1.000 8 1.85  0.000094 1.000 Thallium 1 Youden outlying laboratory 2 Data not available 3 9.05  0.000149 1.000 4 0.54  0.000018 0.989 5 0.84 0.000062 0.997 0.86 0.000004 0.999 6 0.99 0.000596 1.000 7 0.91  0.000446 1.000 8 4.40  0.000099 1.000 Zinc 1 0.41  0.000377 0.991 2 Data not available 3 1.90 0.000509 1.000 2.04  0.000437 0.996 4 0.46 0.011896 0.919 5 Youden outlying laboratory 6 0.07  0.000079 0.996 7 0.12  0.000573 1.000 8 0.34 0.000673 1.000 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 26 5.3.3 Calibration Verification Method 1638 requires that each laboratory analyze calibration verification ( CalVer) samples immediately following calibration and after every ten samples. The calibration verification is conducted by analyzing the mid point calibration standard. Of the 514 calibration verification results reported, 510 were within the draft Method 1638 QC acceptance criteria. Calibration verification results were subjected to outlier testing before being used to develop revised QC acceptance criteria ( Section 6.3). CalVer samples that were used for acceptance criteria development are summarized in Table 5 6. CalVer sample results are shown in Appendix B, Table 7.

Table 5 6. Percent Recoveries for Calibration Verification Samples Analyte Lab1 n Average Recovery (%) Recovery Range %

Sb 1 Youden Outlying Laboratory2 2 11 99 95 102 3 14 101 95 107 4 2 91 90 91 5 8 103 101 105 7 7 101 98 104 8 7 98 94 100 Cd 1 5 101 100 104 2 16 99 95 102 3 10 100 97 103 4 2 105 105 105 5 9 103 100 108 6 Youden Outlying Laboratory2 7 7 103 101 105 8 7 99 96 101 Cu 1 Youden Outlying Laboratory2 2 12 100 92 112 3 14 101 93 110 4 2 109 108 110 5 5 97 94 99 7 7 95 92 99 8 7 95 90 99 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 5 6. Percent Recoveries for Calibration Verification Samples Analyte Lab1 n Average Recovery (%) Recovery Range %

Draft  December 2000 27 Pb 1 Youden Outlying Laboratory2 2 10 99 95 100 3 14 101 98 107 4 2 102 101 102 5 9 102 98 105 7 7 99 98 100 8 7 101 98 104 Ni 1 5 100 99 103 2 Youden Outlying Laboratory2 3 14 97 91 104 4 2 105 103 107 5 9 95 88 102 7 7 94 91 100 8 7 96 93 99 Se 1 5 101 97 106 2 11 98 94 103 3 10 104 99 110 4 2 108 107 109 5 6 98 86 108 7 7 96 93 100 8 7 99 95 102 Ag 1 5 96 93 99 2 20 99 92 107 3 10 103 95 105 4 Youden Outlying Laboratory2 5 9 104 101 108 7 7 102 101 103 8 7 100 98 102 Tl 1 5 101 99 103 2 18 99 91 110 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 5 6. Percent Recoveries for Calibration Verification Samples Analyte Lab1 n Average Recovery (%) Recovery Range %

Draft  December 2000 28 3 10 100 97 107 4 2 90 89 90 5 9 104 100 107 7 Youden Outlying Laboratory2 8 7 102 97 105 Zn 1 5 101 99 103 2 16 97 88 106 3 14 99 92 107 4 2 103 102 104 5 Youden Outlying Laboratory2 7 7 97 95 101 8 7 98 94 100 1Laboratory 5 did not prepare and analyze calibration verification samples 2The laboratory's data package was rejected for this analyte using Youden's laboratory ranking Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 29 5.3.4 Initial and Ongoing Precision and Recovery ( IPR/ OPR)

Draft Method 1638 required each laboratory to analyze at least four reagent water samples spiked with the analytes of interest prior to use of the method ( IPR analyses) and one reagent water sample spiked with the analytes of interest with each analytical batch ( OPR analyses). Laboratories reported results for as many as 12 IPR analyses and as many as 15 OPR analyses.

The IPR/ OPR sample results were screened for outliers before being used to develop QC acceptance criteria. In addition, all results generated from IPR/ OPR samples spiked below the draft method ML were excluded. The precision and recovery data used in development of IPR/ OPR QC acceptance criteria ( Section 6.4) are summarized in Table 5 7. Table 4 in Appendix B contains all IPR and OPR data submitted for this study.

Table 5 7. Precision and Recovery Samples Analyte QC attribute Lab1 Overall2 1 2 3 4 5 6 7 8 Sb IPR Mean Rec. (%)

Youden Outlying Laboratory3 108 110 125 114 110 102 107 114 Std dev 5 2 13 2 6 2 3 8 N 4 4 11 6 6 4 4 39 OPR Mean Rec. (%) 99 11 97 119  91 94 104 Std dev 12 2 1 20  5 10 13 N 10 3 5 9  2 3 32 Cd IPR Mean Rec. (%) 100 98 98 103 110 Youden Outlying Laboratory3 85 87 100 Std dev 6 8 3 5 5 1 5 5 N 4 4 4 12 8 4 4 40 OPR Mean Rec. (%) 99 102 101 107 121 85 99 105 Std dev 18 10 3 1 7 2 10 8 N 2 12 3 5 9 3 3 37 Cu IPR Mean Rec. (%)

Youden Outlying Laboratory3 115 Spiked below draft method ML 4 115 125 110 94 Spiked below draft method ML 4 113 Std dev 21 11 18 4 1 13 N 4 12 6 6 4 32 OPR Mean Rec. (%) 117 110 100  92 107 Std dev 15 2 8  2 10 N 8 5 9  3 25 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 5 7. Precision and Recovery Samples Analyte QC attribute Lab1 Overall2 1 2 3 4 5 6 7 8 Draft  December 2000 30 Pb IPR Mean Rec. (%)

Youden Outlying Laboratory3 125 97 107 137 102 99 103 111 Std dev 3 2 3 8 2 1 1 4 N 3 4 12 8 6 4 4 41 OPR Mean Rec. (%) 105 93 106 114  108 106 107 Std dev 19 2 2 4  14 4 11 N 7 3 5 9  3 3 30 Ni IPR Mean Rec. (%) 107 Youden Outlying Laboratory2 Spiked below draft method ML 4 104 99 103 96 Spiked below draft method ML 4 102 Std dev 2 2 8 3 1 4 N 4 12 8 6 4 34 OPR Mean Rec. (%) 98 105 98  92 99 Std dev 2 2 5  2 4 N 2 5 9  3 19 Se IPR Mean Rec. (%)

Spiked below draft method ML 4 90 106 103 90 Youden Outlying Laboratory3 96 103 98 Std dev 8 2 4 11 1 3 6 N 4 4 12 8 4 4 36 OPR Mean Rec. (%) 123 94 105 108 96 92 106 100 Std dev 2 14 9 2 23 2 6 15 N 2 8 3 5 10 3 3 34 Ag IPR Mean Rec. (%) 103 104 85 Youden Outlying Laboratory3 115 107 101 108 105 Std dev 4 1 0 3 3 2 4 4 N 4 4 4 8 6 4 8 34 OPR Mean Rec. (%) 93 98 86 119  100 104 103 Std dev 10 4 3 18  2 1 10 N 2 15 3 10  3 3 36 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 5 7. Precision and Recovery Samples Analyte QC attribute Lab1 Overall2 1 2 3 4 5 6 7 8 Draft  December 2000 31 Tl IPR Mean Rec. (%) 104 133 102 96 126 96 Youden Outlying Laboratory3 98 107 Std dev 7 4 1 3 10 9 4 6 N 4 4 4 12 8 6 4 42 OPR Mean Rec. (%) 93 83 103 93 119  110 98 Std dev 11 13 7 1 15  4 12 N 2 14 3 5 9  3 36 Zn IPR Mean Rec. (%) 90 129 104 115 Youden Outlying Laboratory3 90 99 116 107 Std dev 4 15 1 14 9 1 10 11 N 4 4 4 12 6 4 4 38 OPR Mean Rec. (%) 95 103 104 102  98 116 103 Std dev 4 22 3 2  4 8 16 N 2 12 3 5  3 2 27 1 Lab 6 did not prepare and analyze OPR samples. 2Overall numbers were calculated as: 1) total number of results, 2) mean recovery of all individual recoveries, 3) weighted mean of standard deviations. 2The laboratory's data package was identified as an outlying laboratory for this analyte using Youden's laboratory ranking.

5.3.5 Matrix Spike and Matrix Spike Duplicate Analyses Method 1638 requires each laboratory to prepare and analyze MS/ MSD samples for each sample batch. Spiking concentrations must be one to five times the background or one to five times the ML, whichever is greater. In developing QC acceptance criteria, EPA used results from all MS/ MSD pairs that were spiked above the draft method ML and were within the laboratory's calibration range. Laboratory 6 reported only MS results, precluding calculation of RPDs. Therefore, MS results from Laboratory 6 were not used in developing MS/ MSD acceptance criteria. The two MS/ MSD samples prepared by Laboratory 8 on the reagent water matrix also were excluded from the QC acceptance criteria calculations because such spikes more closely represent an OPR sample than a matrix spike sample.

MS/ MSD sample results were subjected to Youden outlier analysis before being used to develop QC acceptance criteria. MS/ MSD sample results used for development of QC acceptance criteria are summarized in Table 5 8 across laboratories, in Table 5 9 across matrices, and in Figure 1 below. Table 3 in Appendix B contains all MS/ MSD data submitted by the laboratories. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 32 Table 5 8. MS/ MSD Percent Recoveries and Relative Percent Differences Across Laboratories Analyte QC attribute Lab Overall1 1 2 3 4 5 7 8 Sb Mean Recovery (%)

Youden Outlying Laboratory2 98 105 94 101 106 102 100 Recovery Range (%) 85 104 89 114 91 95 85 138 102 116 86 109 85 138 Mean RPD (%) 2 2 2 8 3 5 3 RPD Range (%) 1 2 1 3 1 4 1 15 0 9 1 13 0 15 Number of Pairs 4 3 4 2 3 3 19 Cd Mean Recovery (%) 103 103 96 102 87 101 98 98 Recovery Range (%) 99 110 92 115 90 103 99 105 43 103 100 103 92 105 43 115 Mean RPD (%) 2 6 1 1 8 1 1 3 RPD Range (%) 0 4 2 13 0 1 1 2 2 19 0 1 0 1 0 19 Number of Pairs 3 4 4 4 4 3 3 25 Cu Mean Recovery (%)

Youden Outlying Laboratory2 108 98 100 86 92 89 96 Recovery Range (%) 97 122 98 99 94 102 63 158 90 95 82 103 63 158 Mean RPD (%) 1 0 1 9 1 2 3 RPD Range (%) 1 2 0 0 0 1 1 18 1 1 2 3 0 18 Number of Pairs 3 1 4 3 3 3 17 Pb Mean Recovery (%)

Youden Outlying Laboratory2 94 95 99 93 90 103 96 Recovery Range (%) 88 99 87 105 96 101 86 97 77 99 99 111 77 111 Mean RPD (%) 2 1 1 1 1 2 1 RPD Range (%) 0 3 0 4 0 2 0 2 0 1 1 4 0 4 Number of Pairs 4 4 4 3 3 3 21 Ni Mean Recovery (%) 96 Youden Outlying Laboratory2 83 95 78 92 92 89 Recovery Range (%) 92 103 79 87 88 98 47 92 88 98 89 98 47 103 Mean RPD (%) 1 0 2 2 1 1 1 RPD Range (%) 1 2 0 0 0 4 0 5 1 1 0 2 0 5 Number of Pairs 3 2 4 4 3 3 19 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 5 8. MS/ MSD Percent Recoveries and Relative Percent Differences Across Laboratories Analyte QC attribute Lab Overall1 1 2 3 4 5 7 8 Draft  December 2000 33 Se Mean Recovery (%) 111 100 108 103 67 95 97 97 Recovery Range (%) 98 129 90 105 99 114 100 105 31 100 89 107 91 104 31 129 Mean RPD (%) 4 4 2 2 6 3 1 3 RPD Range (%) 3 7 1 9 0 5 1 3 2 12 2 5 0 2 0 12 Number of Pairs 3 4 4 4 4 3 3 25 Ag Mean Recovery (%) 94 90 93 Youden Outlying Laboratory2 89 98 98 93 Recovery Range (%) 84 100 85 96 85 99 59 106 97 100 89 122 59 122 Mean RPD (%) 3 2 1 2 0 6 2 RPD Range (%) 1 5 1 4 1 2 1 3 0 0 1 13 0 13 Number of Pairs 3 4 4 4 3 3 21 Tl Mean Recovery (%) 102 101 104 88 113 Youden Outlying Laboratory2 105 102 Recovery Range (%) 98 105 88 107 99 110 84 90 57 140 97 111 57 140 Mean RPD (%) 1 3 2 1 6 2 3 RPD Range (%) 1 3 0 6 0 4 0 2 1 14 1 3 0 14 Number of Pairs 3 4 4 4 4 3 22 Zn Mean Recovery (%) 96 104 91 99 Youden Outlying Laboratory2 98 102 99 Recovery Range (%) 95 97 91 114 77 106 96 102 92 106 80 164 77 164 Mean RPD (%) 3 2 5 1 1 4 2 RPD Range (%) 3 3 0 4 1 15 0 1 0 1 0 10 0 15 Number of Pairs 1 4 4 4 3 3 19 1Overall numbers were calculated as: 1) mean recovery of all individual recoveries, 2) overall recovery range, 3) weighted mean RPD of all laboratory mean RPDs, 4) overall RPD range, and 5) total number of pairs. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 34 Table 5 9. MS/ MSD Percent Recoveries and Relative Percent Differences Across Matrices Analyte QC attribute Matrix Overall1 Filtered Freshwater Filtered Effluent Unfiltered Effluent Sb Mean Recovery (%) 101 98 102 100 Recovery Range (%) 85 138 85 116 94 107 85 138 Mean RPD (%) 4 3 1 3 RPD Range (%) 0 15 1 9 0 2 0 15 Number of Pairs 10 5 4 19 Cd Mean Recovery (%) 101 99 95 98 Recovery Range (%) 90 108 86 110 43 115 43 115 Mean RPD (%) 2 2 6 3 RPD Range (%) 0 4 0 7 0 19 0 19 Number of Pairs 11 7 7 25 Cu Mean Recovery (%) 95 93 99 96 Recovery Range (%) 63 122 82 99 64 158 63 158 Mean RPD (%) 3 1 3 3 RPD Range (%) 0 18 0 3 1 9 0 18 Number of Pairs 8 4 5 17 Pb Mean Recovery (%) 97 95 94 96 Recovery Range (%) 86 111 87 104 77 105 77 111 Mean RPD (%) 1 1 2 1 RPD Range (%) 0 4 0 2 1 4 0 4 Number of Pairs 10 6 5 21 Ni Mean Recovery (%) 93 89 84 89 Recovery Range (%) 85 103 79 98 47 98 47 103 Mean RPD (%) 1 2 1 1 RPD Range (%) 0 3 0 4 0 5 0 5 Number of Pairs 8 6 5 19 Se Mean Recovery (%) 101 95 93 97 Recovery Range (%) 73 129 61 107 31 112 31 129 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 5 9. MS/ MSD Percent Recoveries and Relative Percent Differences Across Matrices Analyte QC attribute Matrix Overall1 Filtered Freshwater Filtered Effluent Unfiltered Effluent Draft  December 2000 35 Mean RPD (%) 3 2 4 3 RPD Range (%) 0 10 0 5 2 12 0 12 Number of Pairs 11 7 7 25 Ag Mean Recovery (%) 99 90 88 93 Recovery Range (%) 85 122 84 97 59 98 59 122 Mean RPD (%) 3 2 1 2 RPD Range (%) 0 13 0 5 0 2 0 13 Number of Pairs 9 6 6 21 Tl Mean Recovery (%) 103 107 96 102 Recovery Range (%) 88 130 84 140 57 107 57 140 Mean RPD (%) 4 1 2 3 RPD Range (%) 0 14 0 3 0 5 0 14 Number of Pairs 10 6 6 22 Zn Mean Recovery (%) 100 98 97 99 Recovery Range (%) 77 164 87 107 80 114 77 164 Mean RPD (%) 4 1 1 2 RPD Range (%) 0 15 0 2 0 2 0 15 Number of Pairs 9 5 5 19 1Overall numbers were calculated as: 1) mean recovery of all individual recoveries, 2) overall recovery range, 3) weighted mean RPD of all laboratory mean RPDs, and 4) overall RPD range, and 5) total number of pairs. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 36 80.0 90.0 100.0 110.0 120.0 Ag (

n=

42) Cd (

n=

50) Cu (

n=

34) Ni (

n=

38) Pb (

n=

42) Sb (

n=

38) Se (

n=

50) Tl (

n=

44) Zn (

n=

38) Distribution of MS/ MSD Recoveries Analyte Percent Recovery Figure 1. Distribution of MS/ MSD Recoveries 5.3.6 Method Blank Analyses Method 1638 requires the analysis of method blanks with each sample batch. The method states that the target analyte may not be present in the method blank at a level equal to or greater than the MDL. If the concentration exceeds the MDL, the laboratory must identify the source of contamination, correct the problem, and re analyze the method blank and all associated samples. In order to assess both potential contamination and instrument drift resulting in negative bias, method blanks were assessed by comparing the absolute value of the method blank result to the revised MDL for the corresponding analyte.

Table 5 10 summarizes the results of all method blanks excluding Youden outliers. Of the 275 method blank results reported, more than 93 percent were below the MDL for the corresponding analyte. Lead was the analyte most commonly reported in method blank exceedances. All method blank results are given in Table 5 of Appendix B. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 37 Table 5 10. Method Blank Results Analyte Revised MDL Mean Method Blank ( µ g/ L) Minimum Method Blank ( µ g/ L) Maximum Method Blank ( µ g/ L) n Number Exceeding Revised MDL Antimony 0.05 0.002  0.019 0.028 24 0 Cadmium 0.08 0.005  0.037 0.292 36 1 Copper 0.13 0.328  0.037 6.364 26 2 Lead 0.015 0.033  0.022 0.859 25 6 Nickel 0.11 0.057  0.002 1.168 22 1 Selenium 0.9  0.001  0.827 0.519 31 0 Silver 0.03 0.018  0.004 0.391 39 5 Thallium 0.015 0.000  0.010 0.015 37 0 Zinc 0.3 0.102  0.245 2.127 35 2 5.3.7 Calibration Blank Analyses Method 1638 requires laboratories to analyze a calibration blank after every calibration verification to demonstrate that there is no carryover and that the analytical system is free from contamination. The target analytes must not be present in the calibration blank at a level equal to or greater than the MDL. If the concentration exceeds the MDL, the laboratory must identify the source of contamination, correct the problem, verify the calibration, and repeat the analysis. Calibration blanks were assessed by comparing the absolute value of the calibration blank results to the revised MDL for the corresponding analyte.

Table 5 11 summarizes the results of all calibration blanks. More than 93 percent of the 539 calibration blank results reported, were below the MDL for the corresponding analyte. As was observed with the method blanks, lead had the highest number of calibration blank exceedances. All calibration blank results are given in Table 5 of Appendix B. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 38 Table 5 11. Calibration Blank Results Analyte Revised MDL Mean Calibration Blank ( µ g/ L) Minimum Calibration Blank ( µ g/ L) Maximum Calibration Blank ( µ g/ L) n Number Exceeding Revised MDL Antimony 0.05 0.012  0.024 0.400 65 3 Cadmium 0.08 0.005  0.130 0.070 62 1 Copper 0.13  0.006  0.109 0.084 62 0 Lead 0.015 0.003  0.085 0.029 59 13 Nickel 0.11  0.003  0.165 0.130 49 4 Selenium 0.9  0.024  1.162 0.516 58 1 Silver 0.03 0.001  0.464 0.049 62 10 Thallium 0.015  0.003  0.200 0.014 62 1 Zinc 0.3  0.018  0.429 0.248 60 2 5.3.8 Standard Reference Material Analyses Each laboratory was required to analyze the National Institute of Science and Technology ( NIST) standard reference material ( SRM) 1643d at least once during Phase 3 of this study. Laboratories 1 and 7 analyzed an additional SRM ( SLRS 4) from the Canadian National Research Council ( NRC). SLRS 4 contained six of the nine target analytes ( excluding silver, selenium, and thallium) at lower levels than 1643d. The concentration of cadmium was below the analytical range of the method and was not considered for evaluation of Method performance. SRM results are summarized in Table 5 12 and presented in Figure 2. All SRM analyses are reported in Appendix B, Table 6. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 39 Table 5 12. SRM Sample Results Analyte SRM Concentration ( ug/ L ) Mean % Recovery Standard Deviation Number of Sample Analyses Number of Labs Antimony NIST 1643 D 54.1 98 4 12 5 SLRS 4 0.23 114 7 3 1 Cadmium NIST 1643 D 6.47 94 3 18 6 Copper NIST 1643 D 20.5 102 9 19 7 SLRS 4 1.8 111 3 3 1 Lead1 NIST 1643 D 18.15 93 12 15 6 Nickel NIST 1643 D 58.1 95 2 11 4 SLRS 4 0.67 106 4 4 2 Selenium NIST 1643 D 11.43 94 14 18 7 Silver NIST 1643 D 1.27 98 6 18 7 Thallium NIST 1643 D 7.28 91 10 16 7 Zinc NIST 1643 D 72.48 95 7 16 6 SLRS 4 0.93 99 3 4 2 1The analytical results from Laboratory 7 showed poor recoveries (~ 5%) for lead. NIST 1643d contains bismuth, and the laboratory used bismuth as an internal standard for lead. The lead results for Laboratory 7 were excluded from this summary information. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 40 80.0 90.0 100.0 110.0 120.0 Ag (

n=

18) Cd (

n=

18) Cu (

n=

22) Ni (

n=

11) Pb (

n=

18) Sb (

n=

15) Se (

n=

18) Tl (

n=

16) Zn (

n=

20) Distribution of SRM Recoveries Analyte Percent Recovery Figure 2. Distribution of SRM Recoveries Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 41 5.3.9 Quality Control Samples Method 1638 requires laboratories to analyze a quality control sample ( QCS) when beginning use of the method, quarterly, or as required to meet data quality needs. Although QCS analysis was not required for this study, four laboratories analyzed at least one QCS. QCS results are summarized in Table 5 13, excluding data from Youden outlying laboratories, and given in Appendix B, Table 6.

Table 5 13. Quality Control Sample Results Analyte Mean % Recovery Number of Samples Number of Samples < 90% Recovery Number of Samples > 110% Recovery Antimony 120 12 0 5 Cadmium 103 14 0 0 Copper 107 16 0 5 Lead 103 16 0 0 Nickel 99 12 0 0 Selenium 105 14 0 2 Silver 101 10 0 0 Thallium 98 14 4 2 Zinc 99 13 1 2 5.4 Silver Recoveries Since initiating this study, EPA has learned of potential problems and interferences in quantifying silver. Laboratory 4 reported silver concentration data for two days of analyses, and noted poor MS/ MSD recoveries for silver on the second day. The laboratory attributed the poor recoveries to degradation of the 10 mg/ L multi element standard used to spike the samples. Analysis of the standard by ICP AES confirmed that the silver concentration was not stable. The laboratory suggested that the problem might be that standards prepared in 0.4% HCl + 0.8% HNO3 acid are not as stable as standards prepared in 1% nitric acid. Laboratory 4 was identified as the Youden outlying laboratory for silver and was not included for development of silver QC acceptance criteria. Table 5 15 shows that all other laboratories reported acceptable silver recovery for QC samples spiked in the laboratory.

Because the QC acceptance criteria developed in this study are based on QC results and the QC sample results do not show low silver recoveries, the QC acceptance criteria developed in this study are considered valid. The field sample results show low silver recovery when compared to the expected sample concentration determined in Phase 2. EPA recognizes that further study may be needed to assess potential interferences and the stability of silver in the presence of acid preservatives. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 42 Table 5 14. Recovery of Silver in QC and Field Samples Lab Mean IPR (% Rec) Mean OPR (% Rec) Mean QCS (% Rec) Mean Cal Ver (% Rec) Mean MS/ MSD (% Rec) Mean Field Dups (% Rec) Mean Youden Pairs (% Rec)

1 103 93  96 94 46 12 2 104 98 102 99 91 64 12 3 85 86  103 91 85 84 4 Youden laboratory outlier 5 115 119 101 104 84 55 26 6 107     70 27 7 101 100  102 98 46 6 8 108 104 101 100 98 45 6 Results of the Interlaboratory Validation Study of EPA Method 1638 8EPA Guide to Method Flexibility and Approval of EPA Water Methods, EPA 821 D 96 004, December 1996.

Draft  December 2000 43 Section 6 Development of QC Acceptance Criteria QC acceptance criteria for Method 1638 were developed using ASTM and AOAC International procedures and procedures given in Chapter 3 of EPA's Guide to Method Flexibility and Approval of EPA Water Methods. 8 Development of these criteria is described in Sections 6.1 through 6.5. Details of statistical analyses are given in Appendix C.

6.1 Method Detection Limit ( MDL) and Minimum Level ( ML)

The latest water quality criteria ( WQC) published by EPA are those listed in the National Toxics Rule ( 57 FR 60848) and the Stay of Federal Water Quality Criteria for Metals ( 60 FR 22228). These rules include water quality criteria for 13 metals including the nine target analytes for Method 1638. In developing Method 1638, EPA set a goal that analytical methods be developed that are capable of achieving MDLs that are one tenth the lowest EPA WQC for that metal. This goal was designed to avoid the need for blank subtraction by ensuring any contributions from contaminant sources ( as measured by blanks) were insignificant ( i. e., < 10% of total sample result) at potential regulatory compliance levels.

To establish MDLs for Method 1638, EPA used results generated during Phase 1 ( presented in Table 5 1). After removing Youden outlying laboratories, pooled MDLs for each analyte were calculated and the pooled and highest MDLs were compared to the MDLs listed in the draft method and to the lowest Water Quality Criterion for each metal. Table 6 1 presents these values. When revising Method 1638, EPA intends to specify the highest MDL achieved among the seven participating laboratories as the MDL criterion for the method. Such MDLs allow for detection of nearly all target metals at least 10 times below the lowest EPA water quality criterion for that metal. It is important to note that the data suggest most laboratories can achieve lower MDLs. Laboratories and regulatory authorities should consider this capability when using Method 1638.

The equations used to calculate pooled MDLs are presented in Appendix C. MLs for each analyte were determined by multiplying the MDL by 3.18 ( or by the appropriate multiplier if the laboratory used more than 7 replicates to determine the MDL), and rounding to the number nearest to ( 1, 2, or 5) x 10n, where n is a positive or negative integer. The 3.18 multiplier is the ratio between the 10 sigma multiplier used to establish the American Chemical Society's ( ACS) limit of quantitation and the Student's t multiplier. The revised MDLs and MLs are given in Table 6 1. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 44 Table 6 1. Revised MDLs and MLs Analyte Draft MDL ( µ g/ L) 1/ 10 WQC ( µ g/ L) Pooled MDL ( µ g/ L) Highest MDL ( µ g/ L) Revised MDL ( µ g/ L) Revised ML ( µ g/ L)

Sb 0.0097 1.4 0.016 0.048 0.05 0.2 Cd 0.025 0.037 0.025 0.077 0.08 0.2 Cu 0.087 0.24 0.056 0.132 0.13 0.5 Pb 0.015 0.054 0.007 0.013 0.015 0.05 Ni 0.33 0.82 0.051 0.111 0.11 0.5 Se 0.45 0.5 0.450 0.892 0.90 2.0 Ag 0.029 0.032 0.013 0.026 0.03 0.1 Tl 0.0079 0.17 0.005 0.015 0.015 0.05 Zn 0.14 3.2 0.109 0.288 0.30 1.0 6.2 Calibration Linearity EPA intends to revise the calibration section in Method 1638 to recommend use of response factor or weighted linear regression and allow unweighted linear regression as acceptable calibration techniques. To ensure that the calibration is linear, the correlation coefficients for unweighted and weighted linear regression must be greater than 0.995 and 0.990, respectively, and the intercept must have an absolute value less than the MDL. A correlation coefficient of 0.995 is the standard limit for assessing calibration linearity using an unweighted regression in analytical methods for metals and a correlation coefficient of 0.990 was judged to allow for equal weighting in the weighted regression.

6.3 Calibration Verification Calibration verification QC acceptance criteria were developed using all calibration verification sample results remaining after data validation ( Section 4) and outlier analysis ( Section 5.3.1). Calculations used to develop QC acceptance criteria are detailed in Appendix C and encompass both between laboratory and within laboratory variability. In general, the calculated recovery limits, shown in Table 6 2, support the calibration verification limits specified in the draft method. Results of the study suggested the need for slightly wider limits for cadmium and silver; EPA intends to modify the draft specifications accordingly. Revised calibration verification QC acceptance criteria reflecting these changes are listed in the last column of Table 6 2. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 45 Table 6 2. Calibration Verification Acceptance Criteria Analyte Draft Recovery Limits (%) Calculated Recovery Limits (%) Revised Recovery Limits (%)

Antimony 90 111 90 111 90 111 Cadmium 91 105 95 107 91 107 Copper 76 120 86 111 76 120 Lead 91 120 96 105 91 120 Nickel 86 116 87 107 86 116 Selenium 69 127 89 111 69 127 Silver 81 107 92 108 81 108 Thallium 82 118 89 111 82 118 Zinc 76 121 89 108 76 121 6.4 Initial and Ongoing Precision and Recovery ( IPR/ OPR)

QC acceptance criteria for IPR/ OPR were developed using all IPR/ OPR sample results remaining after data validation and outlier analysis. Calculations were modified from ASTM guidelines and EPA's Guide to Method Flexibility and Approval of EPA Water Methods to handle a different number of results per laboratory. ASTM and EPA guidelines concerning the development of QC acceptance criteria for IPR/ OPR results assume that all labs generate the same number of results ( i. e., a constant " n" among labs). To allow development of criteria based on all valid IPR/ OPR data submitted by each laboratory, the ASTM and EPA guidelines were slightly modified and degrees of freedom were calculated using Satterthwaite's method. Calculations used to develop QC acceptance criteria are detailed in Appendix C and encompass both between laboratory and within laboratory variability. In general, the calculated recovery limits, shown in Table 6 3, support the calibration verification limits specified in the draft method. Results of the study suggested the need for wider recovery limits for antimony, cadmium, and silver; EPA intends to modify the draft specifications accordingly. Revised IPR/ OPR QC acceptance criteria reflecting these changes are listed in the last column in Table 6 3 and 6 4. Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 46 Table 6 3. IPR Acceptance Criteria Analyte Draft Recovery and Standard Deviation Limits Calculated Recovery and Standard Deviation Limits Revised Recovery and Standard Deviation Limits s X s X s X Antimony 20 81 120 19 90 128 20 81 128 Cadmium 13 85 112 12 79 126 13 79 126 Copper 43 55 141 20 89 132 43 55 141 Lead 30 75 140 15 87 132 30 75 140 Nickel 30 71 131 7 90 112 30 71 131 Selenium 41 63 145 19 79 119 41 63 145 Silver 19 82 120 13 81 127 19 81 127 Thallium 30 66 134 23 78 128 30 66 134 Zinc 43 55 142 22 83 128 43 55 142 Table 6 4. OPR Verification Acceptance Criteria Analyte Draft Recovery Limits (%) Calculated Recovery Limits (%) Revised Recovery Limits (%)

Antimony 79 122 81 138 79 138 Cadmium 84 113 77 128 77 128 Copper 51 145 80 141 51 145 Lead 72 143 82 137 72 143 Nickel 68 134 89 113 68 134 Selenium 59 149 72 126 59 149 Silver 74 119 78 130 74 130 Thallium 64 137 68 137 64 137 Zinc 46 146 73 138 46 146 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 47 6.5 Matrix Spike/ Matrix Spike Duplicate ( MS/ MSD) Recovery and Relative Percent Difference ( RPD)

QC acceptance criteria for MS/ MSD precision and recovery were developed using MS/ MSD sample results remaining after data validation and outlier analysis. These samples included filtered freshwater, filtered effluent, and unfiltered effluent matrices. Calculations used to develop QC acceptance criteria are detailed in Appendix C and encompass both between laboratory and within laboratory variability. These calculations reflect the statistical procedures recommended by ASTM and EPA guidance with modifications to allow for calculation of degrees of freedom using Satterthwaite's method. Details of these calculations are presented in Appendix C, and the calculated MS/ MSD QC acceptance criteria are listed in Table 6 4.

In most cases, the calculated recovery and RPD limits for the spiked matrix samples supported the limits given in the draft method. EPA intends to retain the draft specifications where supported by the data from this study. EPA intends to slightly widen some specifications to reflect study results and ensure that neither the upper or lower recovery limits for the matrix spike samples are more restrictive than their corresponding limit in the OPR samples ( which are prepared in reagent water).

Table 6 5. MS/ MSD Acceptance Criteria Analyte Draft Recovery and RPD Limits Calculated Recovery and RPD Limits Revised Recovery RPD Limits RPD X RPD X RPD X Antimony NA 79 122 29 79 122 29 79 138 Cadmium NA 84 113 17 75 122 17 75 128 Copper NA 51 145 52 59 132 52 51 145 Lead NA 72 143 11 81 111 11 72 143 Nickel NA 68 134 7 64 115 7 64 134 Selenium NA 59 149 17 57 137 17 57 149 Silver NA 74 119 11 70 117 11 70 130 Thallium NA 64 137 17 70 133 17 64 137 Zinc NA 46 146 31 68 129 31 46 146 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 48 Section 7 Data Analysis and Discussion Data were gathered in this study to characterize the overall performance of Method 1638 and to identify areas of the method, including QC acceptance criteria, requiring further revision. Areas requiring revision were discussed previously in this report and are summarized in Section 8. The remainder of this section focuses on overall method performance. Section 7.1 discusses performance of the method in each of the matrices tested during the study; Section 7.2 discusses the method's performance across matrices and laboratories.

7.1 Matrix Specific Performance of Method 1638 In conducting this study, EPA sought to determine if Method 1638 was capable of yielding reliable results in the variety of matrices to which the method might be applied, including ambient freshwater samples, and filtered and unfiltered point source discharges. To assess the method's performance in each matrix, percent recoveries were determined for each sample at each concentration in each matrix. Mean percent recoveries and standard deviations ( SDs) were then determined for each matrix in each laboratory. The standard deviations determined by calculating the square root of the weighted mean of all laboratory variances in a given matrix. The average percent recoveries were determined by calculating the mean of all laboratory mean recoveries for a given matrix. Table 7 1 presents the results of this analysis using 1) field samples only, 2) MS/ MSD samples only, and 3) a combination of field and MS/ MSD samples. These results demonstrate that the method performs comparably across matrix types.

Table 7 1. Pooled Matrix Specific Precision and Recovery Field Samples MS/ MSD Samples Field + MS/ MSD Samples Analyte Matrix Mean % Rec1 Precision ( SD) n Mean % Rec Precision ( SD) n Mean % Rec1 Precision ( SD) n Antimony Filtered Effluent 105 8 13 98 4 10 102 7 23 Unfiltered Effluent 95 1 11 102 1 8 98 4 19 Freshwater 99 8 42 99 2 8 99 8 50 Reagent Water 78 12 40       78 12 40 Cadmium Filtered Effluent 95 18 14 99 4 14 97 18 28 Unfiltered Effluent 95 3 14 95 8 14 95 21 28 Freshwater 101 6 14 101 3 14 101 9 28 Reagent Water 97 3 28       97 3 28 Copper Filtered Effluent 103 3 12 92 2 6 99 7 18 Unfiltered Effluent 110 8 14 99 30 10 105 19 24 Freshwater 116 74 55 96 8 14 112 67 69 Reagent Water 113 31 41       113 31 41 Lead Filtered Effluent 124 11 14 95 1 12 110 18 26 Unfiltered Effluent 108 2 13 94 3 10 102 5 23 Results of the Interlaboratory Validation Study of EPA Method 1638 Table 7 1. Pooled Matrix Specific Precision and Recovery Field Samples MS/ MSD Samples Field + MS/ MSD Samples Analyte Matrix Mean % Rec1 Precision ( SD) n Mean % Rec Precision ( SD) n Mean % Rec1 Precision ( SD) n Draft  December 2000 49 Freshwater 135 41 41 98 3 12 123 44 61 Reagent Water 109 21 39       109 21 39 Nickel Filtered Effluent 96 3 13 89 2 12 92 6 25 Unfiltered Effluent 96 5 14 84 2 10 91 15 24 Freshwater 99 8 42 94 2 10 98 9 52 Reagent Water 92 1 23       92 1 23 Selenium Filtered Effluent 141 4 14 95 4 14 118 32 28 Unfiltered Effluent 136 6 14 93 5 14 114 30 28 Freshwater 92 10 22 103 7 14 96 12 36 Reagent Water 99 5 38       99 5 38 Silver Filtered Effluent 77 10 14 90 3 12 83 13 26 Unfiltered Effluent 46 2 14 88 1 12 65 26 26 Freshwater 43 20 28 99 6 12 60 35 40 Reagent Water 45 36 42       45 36 42 Thallium Filtered Effluent 98 4 13 111 2 10 103 11 23 Unfiltered Effluent 98 4 14 96 9 12 97 11 26 Freshwater 96 4 28 105 4 12 99 8 40 Reagent Water 94 6 48       94 6 48 Zinc Filtered Effluent 100 5 14 98 2 10 99 5 24 Unfiltered Effluent 102 1 13 97 3 10 100 7 23 Freshwater 110 47 42 99 16 12 108 43 54 Reagent Water 102 14 42       102 14 42 * Percent recoveries of field samples were calculated using expected concentrations in Table 2 1 and Appendix B, Table 1.

7.2 Overall Performance of Method 1638 Mean precision and recovery results for IPR, OPR, QCS, MS/ MSD, blind duplicate and Youden sample pairs analyzed by each of the participating laboratories during Phase 3 are summarized in Table 7 2, along with the pooled results across laboratories. In addition, the distribution of field duplicates RPDs is presented in Figure 3. With the exception of the antimony and copper QCS values reported by Laboratory 4 the mean percent recoveries of all QC samples were within the revised QC acceptance criteria. With the exception of pooled antimony recovery, the results of all QC acceptance criteria pooled across laboratories Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 50 0.0 10.0 20.0 30.0 Ag (

n=

35) Cd (

n=

35) Cu (

n=

38) Ni (

n=

31) Pb (

n=

37) Sb (

n=

31) Se (

n=

40) Tl (

n=

40) Zn (

n=

34) Distribution of Field Duplicate RPDs Analyte Relative Percent Difference also were within the revised QC acceptance criteria These results support application of Method 1638 to the determination of trace levels of antimony, cadmium, copper, lead, nickel, selenium, silver, thallium, and zinc in all study matrices.

Figure 3. Distribution of Field Duplicate RPDs 51 Table 7 2. Laboratory Precision and Recovery Performance Using EPA Method 1638 Analyte Lab IPR OPR QCS SRM Cal Ver MS/ MSD Phase 3 Duplicates Phase 3 Youden Pairs Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RPD Mean % Rec RPD Mean % Rec RPD Antimony 1 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking.

2 108 5 96 7 103 2 99  99 2 96 2 86 2 96 2 3         101 3 102 2 84 3 97 1 4   97 1 130 26 95 1 91 1 94 1 86 4 96 1 5 91 47       103 1 87 1 73 1 96 3 6       99 3     92 6 101 4 7       107 9 101 2 108 5 86 3 100 1 8 107 3 94 11 107 1 107  98 2 107 1 88 2 108 10 Pooled 100 34 96 6 120 21 101 6 100 2 99 2 86 3 99 3 Cadmium 1 100 6 99 18   94  101 2 103 2 92 5

2 98 8 102 10 101 2 93 6 99 2 106 7 94 13

3         100 2 94 1 102 3

4 103 5 107 1 105 2 95 1 105 0 102 1 96 14

5 110 5 121 6 102 2 94 2 103 2 83 10 117 3

6 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking.

7 85 1 85 3   91 0 103 2 101 1 85 6

8     104 7 91  99 3 98 1 94 3

Pooled 101 5 106 8 104 4 94 3 101 2 98 3 97 7

Copper 1 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking. Table 7 2. Laboratory Precision and Recovery Performance Using EPA Method 1638 Analyte Lab IPR OPR QCS SRM Cal Ver MS/ MSD Phase 3 Duplicates Phase 3 Youden Pairs Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RPD Mean % Rec RPD Mean % Rec RPD 52 2 115 18 117 13 109 8 107 8 100 6 108 1 163 26 106 7 3       103  101 5 98 0 113 10 92 5 4 115 9 110 2 112 4 112 1 109 1 102 1 127 18 113 10 5 125 15 100 8 99 1 96 4 97 2 88 5 107 5 141 37 6 110 3     97 3     117 20 100 2 7       102 10 95 2 92 1 98 2 94 1 8     98 4 92  95 3 89 2 96 2 92 2 Pooled 116 11 109 9 106 5 103 7 99 5 96 2 118 12 105 9 Lead 1 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking.

2 134 14 105 18 100 3 71 13 99 2 96 2 118 9 225 24 3 97 2 93 2   102  101 2 94 2 114 4 138 6 4 107 3 106 2 106 3 98 2 102 1 98 1 109 6 120 3 5 137 6 114 4 100 1 86 6 102 2 92 1 128 13 139 28 6 102 2     108 3     118 2 141 3 7 99 1 108 13     99 1 90 1 98 1 114 1 8 103 1 106 4 101 1 97  101 2 103 2 103 3 101 3 Pooled 113 5 107 10 103 3 93 5 101 2 96 1 112 5 140 10 Nickel 1 107 1 98 2   104  100 2 96 1 93 5 102 3 2 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking. Table 7 2. Laboratory Precision and Recovery Performance Using EPA Method 1638 Analyte Lab IPR OPR QCS SRM Cal Ver MS/ MSD Phase 3 Duplicates Phase 3 Youden Pairs Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RPD Mean % Rec RPD Mean % Rec RPD 53 3       92  97 5 79 0 93 2 99 4 4 104 2 105 2 99 4 96 1 105 3 95 2 103 2 112 4 5 99 8 98 5 100 2   95 6 74 2 103 5 118 1 6 103 3     96 4     85 11 69 2 7 96 1 92 2   100 8 94 3 92 1 94 1 99 3 8     101 5   96 2 92 1 96 2 104 2 Pooled 102 4 99 4 100 4 98 6 97 4 89 1 95 4 100 3 Selenium 1   123 2   111  101 4 111 4 134 6 96 2 90 9 94 15 101 7 85 31 98 3 102 3 114 9 53 3 106 2 105 9   101  104 4 107 2 123 2 95 4 103 4 108 1 108 2 107 2 108 2 102 2 110 2 88 5 90 12 96 24 95  88 8 98 9 64 8 113 3 111 6 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking.

7 96 1 92 2   83 3 96 3 95 3 95 2 85 8 103 3 106 6 103 1 89  99 2 97 1 99 5 91 Pooled 98 7 100 16 105 3 94 12 100 4 97 3 112 4 93 Silver 1 103 3 93 10   83  96 2 94 3 46 5 12 51 2 104 1 98 5 102 3 96 4 99 4 91 3 64 8 12 78 3 85 1 86 4   94  103 3 91 1 85 4 84 9 Table 7 2. Laboratory Precision and Recovery Performance Using EPA Method 1638 Analyte Lab IPR OPR QCS SRM Cal Ver MS/ MSD Phase 3 Duplicates Phase 3 Youden Pairs Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RPD Mean % Rec RPD Mean % Rec RPD 54 4 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking.

5 115 3 119 15 101 1 99 4 104 2 84 1 55 11 26 23 6 107 3     109 4     70 4 27 41 7 101 2 100 2   99 1 102 1 98 0 46 20 6 31 8 108 7 104 1 101 3 100  100 2 98 6 45 53 6 101 Pooled 105 3 103 9 102 3 98 3 100 3 93 2 59 15 25 48 Thallium 1 104 7 93 11   103  101 2 102 1 87 4 86 1 2 133 3 83 16 103 6 79 9 99 5 105 3 100 8 101 5 3 102 1 103 6   100  100 3 105 2 101 3 101 2 4 96 3 93 1 90 4 91 2 90 1 90 0 88 2 87 0 5 126 8 119 13   98  104 2 111 4 98 3 98 3 6 96 10     106 2     102 3 103 3 7 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking.

8 98 4 110 4 110 14 98  102 3 105 2 96 2 90 1 Pooled 107 6 98 13 98 7 91 5 100 4 104 2 96 4 95 2 Zinc 1 90 4 95 5     101 2 96 3 93 5 94 10 2 129 12 95 13 104 8 95 3 97 6 105 2 129 14 130 13 3 104 1 104 2   108  99 5 90 2 103 7 100 7 4 115 12 102 2 96 9 99 1 103 1 98 0 99 5 91 29 Table 7 2. Laboratory Precision and Recovery Performance Using EPA Method 1638 Analyte Lab IPR OPR QCS SRM Cal Ver MS/ MSD Phase 3 Duplicates Phase 3 Youden Pairs Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RSD Mean % Rec RPD Mean % Rec RPD Mean % Rec RPD 55 5 The laboratory's data package was rejected for this analyte using Youden's laboratory ranking.

6 90 10     96 3     112 24 106 4 7 99 1 98 4   83 3 97 2 98 1 93 1 85 3 8     94 8 94  98 2 102 4 134 8 85 4 Pooled 106 10 98 10 98 8 95 2 98 5 98 2 109 9 99 10 Results of the Interlaboratory Validation Study of EPA Method 1638 Draft  December 2000 56 Section 8 Conclusion and Discussion Results of this study demonstrate the ability of EPA Method 1638 to provide reliable data for determination of target analytes in reagent water, freshwater, and effluent with slight modifications to clarify certain QC requirements and to adjust QC acceptance criteria. The Study results also suggest that further investigation of stability of silver in the presence of acid preservatives is needed.

Specific modifications suggested by this study include: C Revision of the calibration requirements ( Section 10.0) to recommend response factor or weighted linear regressions and allow for unweighted linear regression. C Revision of the IPR and OPR analyses ( Sections 9.2.2 and 9.7, respectively) to require laboratories to spike IPR and OPR samples at 1 5 times the ML instead of 2 3 times the ML. This change will standardize the method with current EPA OW policies. C Clarification of the OPR requirements to require an OPR to be prepared and analyzed with each analytical batch. C Clarification of the MS/ MSD requirements ( Section 9.3) to explicitly that an MSD sample must be prepared and analyzed; C Revision of the method and calibration blank requirements ( Sections 9.6.1 and 10.6 respectively) will be revised to require that the absolute value of the blanks for the target analytes be less than the MDL; and C Method blank requirements will be clarified to require a method blank to be prepared and analyzed with each analytical batch.

With these results, EPA Method 1638 can be considered valid for the determination of dissolved and total antimony, cadmium, copper, lead, nickel, selenium, silver, thallium, and zinc in aqueous matrices at water quality criteria levels. Draft  December 2000 Appendix A Study Plan Results of the Interlaboratory Study of EPA Method 1638 Appendix A A 1 Study Plan for Collaborative Validation of Trace Metals Methods 1631, 1632, 1636, 1637, 1638, 1639, and 1640 Prepared for William A. Telliard U. S. Environmental Protection Agency Office of Water Office of Science and Technology Engineering and Analysis Division ( 4303) 401 M Street, SW Washington, D. C. 20460 Prepared by DynCorp Environmental 300 North Lee Street Alexandria, Virginia 22314 Prepared under EPA Sample Control Center Contract No. 68 C3 0337 February 1997 Results of the Interlaboratory Validation Study of EPA Method 1638 Appendix A A 2 Draft  December 2000 Acknowledgments This study plan was prepared under the direction of William A. Telliard of the Engineering and Analysis Division within the U. S. Environmental Protection Agency ( EPA) Office of Water. It was prepared by DynCorp Environmental under EPA Contract No. 68 C3 0337.

Disclaimer This document has been reviewed and approved by the EPA Engineering and Analysis Division. Mention of company names, trade names, or commercial products does not constitute endorsement or recommendation for use. Results of the Interlaboratory Study of EPA Method 1638 Appendix A Draft  December 2000 A 3 TABLE OF CONTENTS SECTION 1: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 SECTION 2: OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1 Phase 1 Objectives  Laboratory Qualification and Selection . . . . . . . . . . . . . . . . . . . . . 2 2.1.1 Method Blank Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.2 Method Detection Limit Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.3 Provision of Time for Gaining Familiarity with the Methods . . . . . . . . . . . . . . . 4 2.2 Phase 2 Objectives  Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2.1 Collect Samples that Represent Multiple Matrices . . . . . . . . . . . . . . . . . . . . . . . 4 2.2.2 Minimize Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2.3 Ensure Homogeneity and Characterize Stability . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2.4 Collect Filtered and Unfiltered Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.5 Collect Samples that Represent Multiple Concentration Ranges . . . . . . . . . . . . . 5 2.2.6 Collect Samples to Allow Evaluation of Intralaboratory Precision . . . . . . . . . . . 5 2.3 Phase 3 Objectives  Method Performance Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.4 Data Quality Objectives for Phases 1 through 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 SECTION 3: STUDY MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 SECTION 4: TECHNICAL APPROACH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1 Phase 1 Technical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.1 Method Blank Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1.2 Method Detection Limit Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2 Phase 2 Technical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2.1 Equipment Cleaning and Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2.2 Field Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2.3 Sample Filtration, Sample Preservation, and Sample Shipment . . . . . . . . . . . . 12 4.2.4 Determination of Field Sample Concentrations . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.5 Generation of Sample Pairs and Homogenization of Samples . . . . . . . . . . . . . 13 4.2.6 Stability Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.3 Phase 3 Technical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 SECTION 5: DATA REPORTING AND EVALUATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 SECTION 6: LIMITATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Results of the Interlaboratory Validation Study of EPA Method 1638 Appendix A A 4 Draft  December 2000 SECTION 1: INTRODUCTION The Clean Water Act requires that ambient water quality criteria ( WQC) published by the United States Environmental Protection Agency ( EPA) reflect the latest scientific knowledge concerning the physical fate of pollutants, the effects of pollutants on ecological and human health and welfare, and the effect of pollutants on biological community diversity, productivity, and stability.

The EPA Office of Water ( OW), EPA Regions, and state permitting authorities are increasing their emphasis on water qualitySbased permitting under the National Pollutant Discharge Elimination System. However, ambient WQC levels for trace metals require measurement capabilities at levels as much as 280 times lower than those required to support technology based permit limits. The WQC associated with trace metals are presented in the National Toxics Rule, published at 57 FR 60848. Although the Agency has long held that analytical detection limits should not be a consideration when calculating WQC ( because detection limits are not related to actual environmental impacts), the ability to make reliable measurements at WQC levels is an obvious goal. This study plan is designed to validate seven 1600 series trace metals methods that have been developed in response to the low level WQC requirements.

In 1993, OW's Engineering and Analysis Division ( EAD), within the Office of Science and Technology, began researching analytical methodology believed to be capable of making measurements at or near WQC levels. In developing these methods, EAD sought to utilize existing instrumentation and technology to the maximum extent possible. EAD also sought to ensure that the methods would provide the quality control ( QC) requirements necessary to demonstrate the reliability of data gathered at the low concentrations associated with WQC. Finally, EAD sought to minimize method development costs by basing its approaches on techniques already in use by marine chemists familiar with measuring metals at ambient levels.

In 1994, EAD developed preliminary drafts of EPA sampling, analysis, and data reporting procedures that could be used to collect reliable metals data for use in water qualitySbased permitting. EAD conducted several studies in 1995 and 1996 aimed at developing new procedures and validating the preliminary procedures in the draft sampling and analysis guidance documents. Results of those studies were used to develop seven draft EPA methods for the analysis of trace metals.

EAD's Analytical Method's Staff ( AMS) updated draft versions of these methods in 1996 to reflect minor editorial corrections and final WQC values published in May 1995 under the Stay of Federal Water Quality Criteria for Metals ( 60 FR 22228). Two of the methods ( Methods 1631 and 1632) were further revised to reflect results of several single laboratory studies that were completed in early 1996. Current versions of the seven draft methods are as follows:

° Method 1631: Mercury in Water by Oxidation, Purge and Trap, and CVAFS. EPA 821 R 96 001, July 1996 ° Method 1632: Inorganic Arsenic in Water by Hydride Generation Quartz Furnace AA. EPA 821 R 96 002, July 1996 Results of the Interlaboratory Study of EPA Method 1638 Appendix A Draft  December 2000 A 5 ° Method 1636: Determination of Hexavalent Chromium by Ion Chromatography. EPA 821 R 96 003, January 1996 ° Method 1637: Determination of Trace Elements in Ambient Waters by Chelation Preconcentration with Graphite Furnace Atomic Absorption. EPA 821 R 96 004, January 1996 ° Method 1638: Determination of Trace Elements in Ambient Waters by Inductively Coupled Plasma Mass Spectrometry. EPA 821 R 96 005, January 1996 ° Method 1639: Determination of Trace Elements in Ambient Waters by Stabilized Temperature Graphite Furnace Atomic Absorption. EPA 821 R 96 006, January 1996 ° Method 1640: Determination of Trace Elements in Ambient Waters by On Line Chelation Preconcentration and Inductively Coupled Plasma Mass Spectrometry. EPA 821 R 96 007, January 1996 EAD's next step in the development of the seven draft methods is to evaluate their performance through a collaborative ( round robin) laboratory study on real world matrices. The design of this study is articulated below.