Ion-mobility spectrometry

Ion-mobility spectrometry (IMS) separates ions based on their size/charge ratios and their interactions with a buffer gas [44], The shape of ions also has an effect on the separation [45]. Following ionization, the ions are introduced into a chamber filled with a neutral gas at controlled pressure [45], The separation proceeds in the presence of a relatively weak field. While IMS alone has great importance in national security applications (e.g., detection of explosives), if coupled with MS - it supports analyses of biomolecular species (proteins, lipid isomers) which cannot be fully resolved by MS alone. Both IMS and MS handle gas-phase ions, which makes them particularly compatible with each other. In IMS, the velocity of the ions is proportional to the electric field with the proportionality factor (K) [44,46]  

IM-MS enabled separation of singly and multiply charged peptides as well as conformers [55] it improves analytical selectivity thus facilitating identification of ions. However, IM-MS can also be used to obtain kinetic and thermochemical data [56]. The temperature of the drift cell (and the buffer gas) can be controlled over a wide range. In some cases. 

L is the drift tube length Q is the ion charge E is the electric field strength k is the Boltzmann constant T is the drift gas temperature (K) 

The simplest form of IMS is TOFIMS, where the speeds of ion travel through the drift tube are registered as the time of arrival at the detector from the fastest to the slowest. In simple systems this is 

Innovations in the held of mass spectrometry are constantly being developed. Often they are initially investigated for basic research and then eventually transferred to more applied areas such as the analyses of contaminants in food. Several advanced mass spectrometric techniques are described in this section, along with possible applications to residue analysis. 

Ion mobility can add an extra dimension of separation when coupled to a mass analyzer. Ion mobility spectrometry (IMS) separates ions according to their interactions with a buffer gas, in addition to differences in their m/z ratios. This can provide separation of ions (i.e., isobaric or conformational isomers), which cannot be accomplished using traditional mass analyzers. It can also be used to reduce interfering chemical noise. Ion mobility separates ions based on how long they take to migrate 

Direct and indirect analysis of polymers and additives using mass spectrometry has been reviewed [4,270], Kreiner [271] has described accelerator analysis. 

Principles and Characteristics Ion mobility spectrometry (IMS) is an instrumental technique for the detection and characterisation of organic compounds as vapours at atmospheric pressure. Modern analytical IMS was created at the end of the 1960s from studies on ion-molecule chemistry with mass spectrometers and from ionisation detectors for vapour monitoring. An ion mobility spectrometer (or plasma chromatograph in the original termininology) was first produced in 1970 [272], 

Ion mobility spectrometry comprises and is governed by two separate processes  

An ion mobility spectrometer consists of a sample-introduction device a drift tube where ionisation and separation of ions takes place and a detector. Ionisation sources of choice include radioactive sources (e.g. a 63Ni foil), photoionisation methods, corona-spray ionisation, flame ionisation and corona discharge. The most common detection method used to measure the 

The IMS response for a compound is strongly dependent on temperature, pressure, analyte concen-tration/vapour pressure, and proton affinity (or elec-tron/reagent affinity). Pressure mainly affects the drift time, and spectral profiles are governed by concentration and ionisation properties of the analyte. Complex interactions among analytes in a mixture can yield an ambiguous number of peaks (less, equal to, or greater than the number of analytes) with unpredictable relative intensities. IMS is vulnerable to either matrix or sample complexity. 

We can draw a very loose analogy with GC in that the ions in IMS act like the mobile phase and the neutral gas as the stationary phase. The mobility quantifies the ease with 

The ion signal is measured as a function of time and should therefore consist of a series of peaks corresponding to ions with different mobilities arising from different chemical compounds in the analyte. Drift tube transit times depend on the length of the tube but are typically on the order of several tens of milliseconds. By comparison, the injection time for ions is 1 ms, and until all of the ions in the injected bunch reach the end of the drift tube, a second bunch of ions cannot be injected. Consequently, the duty cycle, which is a measure of the fraction of ions that reach the detector out of the total number of ions that could reach the detector if the experiment was not pulsed, is rather low and is typically 1%. This is an important factor in limiting the sensitivity of IMS. Nevertheless, detection of compounds 

The main drawback with IMS is its inherently poor selectivity. As with GC, many compounds cannot be fully separated by IMS, and even if they are separated it may not be easy to establish their identities. To try and rectify this, IMS has been coupled with mass spectrometry [6], but this comes at the expense of increased cost, complexity and size of the instrument. A notable development is Hadamard transform IMS [7,8], which promises to resolve the problem of the low duty cycle of conventional IMS and should therefore result eventually in a significantly improved sensitivity, although again this delivers a more complex instmment. 

PTR-MS has its origins in the development of the flowing afterglow (FA) method for the study of ion-molecule reaction kinetics. This so-called ion-swarm technique was introduced in the 1960s by Ferguson and co-workers and it revolutionized the study of ion-molecule reaction kinetics and thermodynamics [9,10]. 

A flow tube is distinct from a drift tube in that the transport mechanism in die former is gas flow driven by a pressure difference between the two ends of the tube, that is, no electric field is involved in transporting ions. 

In an electric field, gas phase ions move at different speed, depending on the size and structure. In a commercial instrument, the ion mobility principle has been included in a Q-ToF mass spectrometer for obtaining high-resolution mass spectrometry (up to 40000 mass resolution). So far, no freestanding ion mobility detectors are commercially available. 

Detected agents Blood, blister, choking and nerve agents plus selected TICs GA, GB, GD, VX, HD, L, pepper spray and mace Nerve, blister, blood and choking agents GA, GB, GD, GF, VX, vesicants, TICs, drugs and explosives 

Simultaneous detection No Yes for nerve and blister agents. To detect irritants the mode must be manually changed Yes No 

Usually detection limits for sulfur mustard are in the region of 0.1 mg m [41-46]. An interesting application of a miniaturized aspiration condenser-type ion mobility spectrometer for fast detection of chemical warfare agents has been reported. The device was tested at the Armed Forces Scientific Institute for Protection Technologies-NBC-Protection, Germany, to evaluate the analytical performance. The spectra of different chemical warfare agents, such as Sarin, Tabun, Soman, US-VX, Sulfur Mustard, Nitrogen Mustard and Lewisite were recorded at various 

Gas chromatography is one of the most universally implemented chromatographic techniques for volatile compounds 

GC-MS detection devices are more commonly used today for the detection of nerve agents [51, 52]. GC-MS under electron impact (El) conditions results in extensive fragmentation, providing structural information. GC-MS under 

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Most ion-molecule techniques study reactivity at pressures below 1000 Pa however, several techniques now exist for studying reactions above this pressure range. These include time-resolved, atmospheric-pressure, mass spectrometry optical spectroscopy in a pulsed discharge ion-mobility spectrometry [108] and the turbulent flow reactor [109]. 

Mie Scattering Particle Sizing -Pyrolysis-Gas Chromatography-Ion Mobility Spectrometry (FemtoScan, ECBC)... 

Table 6.42 Main characteristics of ion mobility spectrometry Advantages...

Today, there are still only a few data available in the literature for IMS. A compilation of available ion mobilities can be found in ref. [279]. Ion mobility spectrometry has been reviewed [280-282a], and a few monographs are available [278,283]. 

Applications Ion mobility spectrometry has found application for military, industrial and forensic purposes. In particular, IMS is used as ... 

G.A. Eiceman and Z. Karpas, Ion Mobility Spectrometry, CRC Press, Boca Raton, FL (1994). 

Snyder, A. P Maswadeh, W. M. Parsons, J. A. Tripathi, A. Meuzelaar, H. L. C. Dworzanski, J. P. Kim, M. G. Field detection of Bacillus spore aerosols with standalone pyrolysis-gas chromatography-ion mobility spectrometry. Field Anal. Chem. Technol. 1999, 3, 315-326. 

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

In electric-field driven separations an electric field causes ions to travel through a matrix, such as a gas, liquid, or gel. The movement is retarded by frictional forces from interaction with the matrix and the ions almost instantly reach a steady-state velocity. This velocity depends on properties of both the sample molecules and the surrounding matrix. The two main types of electric-field driven separations are ion mobility spectrometry where the matrix is a gas and electrophoresis where the matrix is a liquid or gel. 

R. Guevremont. High-Field Asymmetric Waveform Ion Mobility Spectrometry A New Tool for Mass Spectrometry. J. Chromatogr., A1058(2004) 3-19. 

SABRE 2000 The portable SABRE 2000, using a scanning system based on IMS (Ion Mobility Spectrometry) can detect drugs, explosives, and chemical warfare agents. More than forty substances can be simultaneously detected and identified in seconds. 

Selection of on-site analytical techniques involves evaluation of many factors including the specific objectives of this work. Numerous instrumental techniques, GC, GC-MS, GC-MS-TEA, HPLC, HPLC-MS-MS, IR, FTIR, Raman, GC-FTIR, NMR, IMS, HPLC-UV-IMS, TOF, IC, CE, etc., have been employed for their laboratory-based determination. Most, however, do not meet on-site analysis criteria, (i.e., are not transportable or truly field portable, are incapable of analyzing the entire suite of analytes, cannot detect multiple analytes compounded with environmental constituents, or have low selectivity and sensitivity). Therefore, there exists no single technique that can detect all the compounds and there are only a few techniques exist that can be fielded. The most favored, portable, hand-held instrumental technique is ion mobility spectrometry (IMS), but limitations in that only a small subset of compounds, the inherent difficulty with numerous false positives (e.g., diesel fumes, etc.), and the length of time it takes to clear the IMS back to background are just two of its many drawbacks. 

R.T. Vinopal, J.R. Jadamec, P. deFur, A.L. Demars, S. Jakubielski, C. Green, C.P. Anderson and J.E.D.R.F. Dugas, Fingerprinting bacterial strains using ion mobility spectrometry, Anal. Chim. Acta, 457 (2005) 83-95. 

Ion mobility spectrometry (IMS) [3,12] is the most widely used instrument for drug detection. The sample is heated to vaporize the analyte, which is then ionized by atmospheric (ambient) pressure chemical ionization (APCI) [3]. The resulting gas-phase ions travel through a drift tube and are separated by their distinct velocities (mobilities) in a weak electrostatic field. IMS instruments use ambient air or nitrogen as the carrier gas, making it particularly adaptable to field applications. 

G. Skopp, Ion mobility spectrometry for the detection of drugs in cases of forensic and criminalistic relevance, Int. J. Ion Mobility Spectrom., 2 (1999) 22-34. 

H. Tsuchihashi, Detection of designer drugs in human hair by ion mobility spectrometry (IMS), Forensic Sci. Int., 94 (1998) 55-63. 

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