Ion-mobility spectrometry

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An ion mobility spectrometer separates ions by shape and charge.

Ion-mobility spectrometry (IMS) is an analytical technique used to separate and identify ionized molecules in the gas phase based on their mobility in a carrier buffer gas. Though heavily employed for military or security purposes, such as detecting drugs and explosives, the technique also has many laboratory analytical applications, recently being coupled with mass spectrometry and high-performance liquid chromatography. IMS devices come in a wide range of sizes (often tailored for a specific application) and are capable of operating under a broad range of conditions. Systems operated at higher pressure (i.e. atmospheric conditions, 1 atm or 1013 mbar) are also accompanied by elevated temperature (above 100 °C), while lower pressure systems (1-20 mbar) do not require heating.




Ion mobility[edit]

Main article: Electrical mobility




The ion mobility K can be experimentally determined by measuring the drift time tD of an ion traversing within a homogeneous electric field the potential difference U in the drift length L:


where Q is the ion charge, n is the drift gas number density, μ is the reduced mass of the ion and the drift gas molecules, k is Boltzmann constant, T is the drift gas temperature, and σ is the ion’s collision cross section with the drift gas. This relation holds approximately at a low electric field limit, where the ratio of E/N is small, at ≤ 6 x 10−17 J•C−1•cm2

A drift tube’s resolving power RP can be calculated as

where tD is the ion drift time, ΔtD is the Full width at half maximum, L is the tube length, E is the electric field strength, Q is the ion charge, k is Boltzmann’s constant, and T is the drift gas temperature.















DMA differential mobility analyzer make use of a fast gas stream perpendicular to the electric field. Thereby ions of different mobilities undergo different trajectories. This type of IMS corresponds to the sector instruments in mass spectrometry. They also work as a scanable filter. Examples include DMD (Differential Mobility Detector), first commercialized in Varian CP-4900 MicroGC.

Drift gas[edit]

The drift gas pressure is an important parameter for the IMS instrument design and resolution. Most drift gases have a higher break down voltage at pressures higher than a few mbar, with the break down voltage increasing as the pressure increases. As an example, high drift voltages of about 10-30 kV can be used with tubes of 1 m length and high gas pressures of 100-1000 mbar to obtain high resolutions. At higher pressures than 10 mbar, ions become more difficult to store. At lower pressures, ions can be stored more easily to obtain an accumulated continuous signal, with the trade-off of lower electric fields (around 10-30 V/cm). Elevated gas temperature assists in removing ion clusters that may distort experimental measurements.[6][7]



Trapped ion mobility spectrometry[edit]

In trapped ion mobility spectrometry (TIMS) ions are held stationary (or trapped) in a flowing buffer gas by an axial electric field gradient (EFG) profile while the application of radio frequency (rf) potentials result in trapping in the radial dimension.[8] TIMS operates in the pressure range of 2 to 5 mbar and replaces the ion funnel found in the source region of modern mass spectrometers. TIMS can be coupled with nearly any mass analyzer through either the standard mode of operation for beam-type instruments, or selective accumulation mode (SAIMS) when used with trapping mass spectrometry (MS) instruments. TIMS devices do not require large size or high voltage in order to achieve high resolution, for instance achieving over 250 resolving power from a 4.7 cm device.[9] In addition TIMS is capable of higher sensitivity than traditional ion mobility systems because no grids or shutters exist in the ion path, improving ion transmission both during ion mobility experiments and while operating in a transparent MS only mode.

Combined IMS methods[edit]

IMS can be combined with other separation techniques.

GC-IMS : gas chromatography - ion mobility spectrometry[edit]

When IMS is coupled with gas chromatography, common sample introduction is with the GC capillary column directly connected to the IMS setup, with molecules ionized as they elute from GC.[4] A similar technique is commonly used for HPLC. A novel design for corona discharge ionization ion mobility spectrometry (CD–IMS) as a detector after capillary gas chromatography has been produced in 2012. In this design, a hollow needle was used for corona discharge creation and the effluent was entered into the ionization region on the upstream side of the corona source. In addition to the practical conveniences in coupling the capillary to IMS cell, this direct axial interfacing helps us to achieve a more efficient ionization, resulting in higher sensitivity.

IMS-MS : ion mobility spectrometry - mass spectrometry[edit]

When IMS is used with mass spectrometry, ion mobility spectrometry-mass spectrometry offers many advantages, including better signal to noise, isomer separation, and charge state identification.[1][10] IMS has commonly been attached to several mass spec analyzers, including quadropole, time-of-flight, and Fourier transform cyclotron resonance.

LC-IMS : liquid chromatography - ion mobility spectrometry[edit]

LC-IMS-MS : liquid chromatography - ion mobility spectrometry - mass spectrometry[edit]

Coupled with LC and MS, IMS has become widely used to analyze biomolecules, a practice heavily developed by David E. Clemmer, now at Indiana University (Bloomington).[5]


Example of Aspiration IMS sensor.

Perhaps ion mobility spectrometry's greatest strength is the speed at which separations occur—typically on the order of tens of milliseconds. This feature combined with its ease of use, relatively high sensitivity, and highly compact design have allowed IMS as a commercial product to be used as a routine tool for the field detection of explosives, drugs, and chemical weapons. Major manufacturers of IMS screening devices used in airports are Morpho and Smiths Detection.


Ions in sensor.

Aspirating IMS is an ion mobility spectrometry technology used to detect low or trace quantities of chemicals in the surrounding atmosphere. It is applied in industrial and military purposes to detect harmful substances in air.[13] Aspiration IMS operates with open-loop circulation of sampled air. Sample flow is passed via ionization chamber and then enters to measurement area where the ions are deflected into one or more measuring electrodes by perpendicular electric field which can be either static or varying. The output of the sensor is characteristic of the ion mobility distribution and can be used for detection and identification purposes.

In metabolomics the IMS is used to detect lung cancer, Chronic obstructive pulmonary disease, Sarcoidosis, potential rejections after Lung transplantation and relations to bacteria within the lung, see Breath gas analysis.

See also[edit]


  1. ^ a b c Kanu AB, Dwivedi P, Tam M, Matz L, Hill HH (January 2008). "Ion mobility-mass spectrometry". J Mass Spectrom. 43 (1): 1–22. doi:10.1002/jms.1383. PMID 18200615. 
  3. ^ Particle Measuring Systems, Inc. “Ion Mobility Spectrometry (IMS) Theory and Applications”
  6. ^ Bengt Nolting, Methods in Modern Biophysics, Springer Verlag, 2005, ISBN 3-540-27703-X
  7. ^ Gary Eiceman & Zeev Karpas, Ion Mobility Spectrometry, CRC Press, 2005, ISBN 0-8493-2247-2
  8. ^ : M. A. Park, Apparatus and Method for Parallel Flow Ion Mobility Spectrometry Combined with Mass Spectrometry, USPN 8,288,717
  9. ^ Silveira, Joshua A.; Ridgeway, Mark E.; Park, Melvin A. (2014). "High Resolution Trapped Ion Mobility Spectrometery of Peptides". Analytical Chemistry: 140528090048009. doi:10.1021/ac501261h. ISSN 0003-2700. 
  10. ^ Fenn LS, McLean JA (June 2008). "Biomolecular structural separations by ion mobility-mass spectrometry". Anal Bioanal Chem. 391 (3): 905–9. doi:10.1007/s00216-008-1951-x. PMID 18320175. 
  13. ^ Riikka-Marjaana Räsänen, Marjaana Nousiainen, Kaleva Peräkorpi, Mika Sillanpää, Lauri Polari, Osmo Anttalainen and Mikko Utriainen. "Analytica Chimica Acta", Volume 623, Issue 1, 8 August 2008, Pages 59-65


  • Joachim Stach, Jörg I. Baumbach: Ion Mobility Spectrometry – Basic Elements and Applications. In: International Journal for Ion Mobility Spectrometry. Vol. 5, Nr. 1, 2002, ISSN 1435-6163, S. 1–21, Digitalisat (PDF; 1,1 MB).

External links[edit]

Listing of analytical instrument sites at DMOZ