**Ion Mobility Spectrometry (IMS)** technique separates gas-phase ionized molecules based on their size-to-charge ratio. Separation is done by mobility differences under electric field in a flow of neutral gas. The advantages of IMS, including compactness and portability of instrumentation, short separation time (milliseconds scale), and low detection limits (ppt – ppb range), allow a wide range of applications.

Experimentally had been see that the mobility *K (cm ^{2}/V·s*) of ions at constant temperature and pressure through a drift gas with density

*N*(m

^{-3}), subject to an high electric field

*E*(V/cm) doesn’t remain constant, and that its dependence with the electric filed (

*E*) can be expressed as

^{[1]}:

*K(E/N) *= *K _{0}* [1 +

*α(E/N)*]

where *E/N* is the normalized electric field and is expressed in Td (Townsends; 1Td=10^{-17}V·cm^{2}) being *K(E/N)* the mobility of the ions and *K _{0}* the mobility coefficient under low or zero field;

*α(E/N)*is a function that takes account of the ion mobility dependence on electric field.

*K*and

_{0}*α*are specific for each type of ion. Mobility is usually considered constant with regard to

*E*, for those ion mobility spectrometers that operate at low E fields (

*E*~7,500 V/cm,

*E/N*<30Td. However, for high values of

*E/N,*

*K*varies become dependent on the electric field

^{[2]}(i.e.

*K = K(E/N)*).

The function *α(E/N)* takes account of the dependence of the ion mobility with the electrical field for a constant gas density, at ambient pressure and temperature. The approximation for the function *α (E/N)* corresponds to a Taylor’s series.

All *α _{2n}* values may be positive and/or negative depending on the ion-neutral potential

*Φ*among other factors. However, none is null and

*α(E/N)*is never exactly zero, though it can be near-zero over a broad range of

*E/N*. The

*n*coefficients could, in principle, be derived

^{[1]}from higher-order collision integrals of the collision cross section using elaborated formalisms that will not be reported here. Experimental measurements have shown that

*α*is three to five orders of magnitude smaller than one and

_{2}*α*is two orders of magnitude smaller than

_{4}*α*. So, in practice, with only two factors, it is enough to calculate the dependence of the mobility with the electric field.

_{2}Different ion mobility spectrometers exist. But in each IMS instrument, four main regions can be identified: sample introduction system; ionization area; drift tube (where separation or selection occurs) and detection area.

### IMS contributions:

**Coupling a branch enclosure with differential Mobility Spectrometry to isolate and measure plant volatiles in contained greenhouse settings**. M.M.McCartney, S.L.Spitulski, A.Pasamontes, D.J.Peirano, M.J.Schirle, R.Cumeras, J.D.Simmons, J.L.Ware, J.F.Brown, A.J.Y.Poh, S.C.Dike, E.K.Foster, K.E.Godfrey, C.E.Davis.*Talanta*,*2016, 146: 148-54*. http://dx.doi.org/10.1016/j.talanta.2015.08.039.

**Review on Ion Mobility Spectrometry. Part 2: Hyphenated Methods and Effects of Experimental Parameters**. R. Cumeras, E.Figueras, C.E.Davis, J.I.Baumbach, I.Gràcia.,*Analyst*, 2015, DOI: 10.1039/c4an01101e.**Analyst HOT article:**http://blogs.rsc.org/an/2014/12/17/hot-articles-in-analyst-43/

**Review on Ion Mobility Spectrometry. Part 1: current instrumentation**. R.Cumeras, E.Figueras, C.E.Davis, J.I.Baumbach, I.Gràcia.*Analyst*, 2015, DOI: 10.1039/c4an01100g.

**A Gas Sensor: the Ion Mobility Spectrometer**. R. Cumeras, ORAL PRESENTATION. In Abstracts of Papers Presented to the First Interdisciplinary phD Student Conference (“Primera joranda d’Investigadors Predoctorals Interdisciplinària”), Pages 11-12. Barcelona, Spain. February, 7^{th}2013.

**Influence of Operational Background Emissions on Breath Analysis using MCC/IMS devices.**R. Cumeras, P. Favrod, K. Rupp, E. Figueras, I. Gràcia, S. Maddula, J.I.Baumbach.,*International Journal for Ion Mobility Spectrometry*, 2012,**15**(2): 69-78. DOI: 10.1007/s12127-012-0094-0.

**Stability and Alignment of MCC/IMS devices.**R.Cumeras, T.Schneider, P.Favrod, E.Figueras, I.Gràcia, S.Maddula, J.I.Baumbach.,*International Journal for Ion Mobility Spectrometry*, 2012,**15**(1): 41-46. DOI: 10.1007/s12127-012-0088-y.

**Modelling a P-FAIMS with Multiphysics FEM.**R.Cumeras, I.Gràcia, E.Figueras, L.Fonseca, J.Santander, M.Salleras, C.Calaza, N.Sabaté, C.Cané.,*Journal of Mathematical Chemistry*, 2012,**50**(2): 359-373. DOI: 10.1007/s10910-010-9772-5.

**Finite-Element Analysis of a Miniaturized Ion Mobility Spectrometer for Security Applications.**R.Cumeras, I.Gràcia, E.Figueras, L.Fonseca, J.Santander, M.Salleras, C.Calaza, N.Sabaté, C.Cané.,*Sensors and Actuators B-Chemistry*, 2012,**170**: 13-20. DOI: 10.1016/j.snb.2010.11.047.

**Modeling Vapor Detection in a Micro Ion Mobility Spectrometer for Security Applications**., R.Cumeras, I.Gràcia, E.Figueras, L.Fonseca, J.Santander, M.Salleras, C.Calaza, N.Sabaté, C.Cané.*Procedia Engineering*, 2010,**5**: 1236-1239. DOI:10.1016/j.proeng.2010.09.336.

**References:**

[1] Mason, E.A. and E.W. McDaniel, Transport properties of ions in gases. 1988, New York: John Wiley & Sons Inc.

[2] Shvartsburg, A.A., Differential Ion Mobility Spectrometry: Nonlinear Ion Transport and Fundamentals of FAIMS. First ed. 2009, Boca Raton, FL: CRC Press.