Investigating Solvent Purity Using Comprehensive Gas Chromatography: A Study of Acetones

Apr 01, 2010

Broad spectrum chemical analysis of trace level components is a continuing challenge for any analytical chemist. This challenge is further confounded when chemical impurities may be present in common organic solvents or when chemical artifacts may be formed, produced and introduced during an analytical procedure. Minimizing and understanding these chemical artifacts is critical for trace level detection and is crucial for accurate analytical conclusions. Comprehensive gas chromatography is an excellent analytical tool to help address these complex mixture challenges. This work examines the impurities present in a variety of acetone sources using comprehensive gas chromatography. This work highlights the extreme variability possible in solvent sources and hence the importance of understanding the impurities that may confound an analytical method or result.

General research or specific experimental protocols involving trace and ultra-trace chemical analysis and detection is an extremely challenging and daunting task for scientists. As well as the inherent chemical background that is present when a sample is collected, numerous chemical analyses and methods rely on a pure solvent for experimental procedures. For example, many chemical extraction approaches use a solvent to extract target chemicals of interest from a substrate (e.g., soil) or collection sorbent. After the extraction step, an evaporation/condensation/concentrating step is performed to reduce the extraction volume to improve detection of trace components. Unfortunately, this volume reduction step will also concentrate many of the impurities present within a solvent and can further confound research efforts. Many of the solvent artifacts introduced into a sample are from chemical impurities that are not completely removed by standard manufacturing processes or techniques for the solvent, as well as the glassware and storage vials used. Regardless of the source, minimizing and understanding these chemical artifacts is critical for trace level detection and is crucial for unambiguous analytical results.

Acetone is one of the most widely used solvents in the laboratory environment. A common chemical production method for acetone is through the cumene process.1 In the cumene process benzene is alkylated with propene resulting in cumene (isopropylbenzene), which is subsequently oxidized to give phenol and acetone. A wide variety of impurities may exist in the final crude acetone fraction (e.g., aliphatic aldehydes, olefins and carbonyl impurities, and more specifically diacetone alcohol, mesityl oxide and hydroxyacetone), which is subsequently purified to obtain the quoted purity. Once the acetone has been obtained in the laboratory, further use or storage may form additional chemical artifacts. Hunchak and Suffet2 and Lafleur and Pangaro3 examined acetone–hexane artifacts produced during a soxhlet extraction process. The chemical artifacts produced through the various procedures and reactions include diacetone alcohol and mesityl oxide as well as phorone, mesitylene and isophorone.2,3

The work presented here examines the purity of various acetone sources using comprehensive gas chromatography and mass spectrometry (GC×GC–MS) for broad spectrum chemical analysis. The purpose of this work is to characterize the impurities present in a solvent as a possible approach to track or match acetone sources for chemical forensic investigations. In particular, in the preparation of the toxin ricin, acetone is a common solvent used for the extraction of the castor oil. Previous work developed a simple solid-phase microextraction (SPME) approach to detect the use of acetone as an extraction solvent in the final crude ricin preparation.4 The motivation for this study is to provide additional sample processing information regarding the type/grade of acetone used in the production of ricin or other extracted materials. As broad spectrum chemical analysis becomes increasingly important GC×GC–MS has emerged as a powerful analytical tool. Comprehensive GC×GC is a multidimensional separation technique that separates a sample sequentially on two different columns, which are chosen to separate mixtures based on distinct — ideally orthogonal — chemical properties. Multidimensional separations have the advantage of greatly improved separations compared to conventional single-dimension approaches.5–9 The work presented here is the first step, examining the impurities present in various acetone sources. However, the overall importance of understanding the possible impurities present in a solvent is vital and can be applied to any trace analytical method.

Experimental Section


Table 1: Acetone source list.
Table 1 lists the 21 acetone sources obtained and examined for this study. The mention of trade names or commercial products in this work does not constitute an endorsement, criticism or recommendation for their use.

Chemical Analysis

Table 2: Experimental conditions for chemical analysis.
Chemical analyses were performed on a Leco Pegasus 4D GC×GC–MS system (LECO, St Joseph, Michigan, USA) equipped with a Gerstel cooled injection system (CIS4) and multipurpose sampler (MPS2) (Gerstel, Baltimore, Maryland, USA). The separation used ultra-high purity helium as the carrier gas, set at 1 mL/min, constant flow. Because the type and number of impurities were largely unknown for each acetone source, two different comprehensive GC×GC column sets were used (see Table 2, A×C and B×C) for all 21 acetone sources. The first dimensional column was either a polar or non-polar type and the secondary column was of moderate polarity and remained constant throughout the study. Unless stated otherwise the experimental conditions are listed in Table 2. LECO ChromaTOF software (version 3.32) was used for data collection and analysis. Higher level data analysis was performed using an in-house software tool (Data Analysis Tool Extension, DAnTE,, which is freely available.