Ion mobility spectrometry, IMS

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],... 

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. 

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. 

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

Ion mobility spectrometry (IMS [43]). Solid phase microextraction (SPME) using a 100 pm polydimethylsiloxane (PDMS) SPME fibre was used for head-space sampling and preconcentration of volatile markers of cocaine, MDMA and marijuana (methyl benzoate, piperonal and terpenes, respectively) in cargo containers. Analysis was then performed by IMS after thermal desorption of the drug markers from the fibre into the IMS analyser. 

Ion mobility spectrometry (IMS) is in worldwide, daily use in laboratories in many fields of chemistry, medicine, food science, and manufacturing and is perhaps the most commonly used technology for detection of explosives at the present time. Its use in forensic laboratories is well known. In fact, it is so well established that there is a journal specializing in IMS [1], A recent book... 

Figure 11.3 Comparison of ion mobility spectrometry (IMS) and mass spectrometry (MS) methods of detection in an overall high-speed screening system.

Chapter 11, Mass Spectrometry for Security Screening of Explosives This chapter is a little different from the other technology descriptions since it describes systems that are not portable. These are systems used to locate explosives in containers, or on personnel, that pass by a fixed point. The chapter also compares the features of mass spectrometry (MS) and ion mobility spectrometry (IMS) that often cause systems developers to choose one or the other for a specific application. 

Ion mobility spectrometry (IMS), which has the ability to separate ionic species at atmospheric pressure, is another technique that is useful for detect and characterising organic vapours in air [97]. This involves the ionisation of molecules and their subsequent drift through an electric field. Analysis is based on analyte separations resulting from ionic mobilities rather than ionic masses. A major advantage of operation at atmospheric pressure is that it is possible to have smaller analytical units, lower power requirements, lighter weight and easier use. 

Roger and Karpas [89] employed neural networks to interpret ion mobility spectrometry (IMS) and XRF spectral data and to derive qualitative and quantitative information from them. 

Rate constants have been measured for the reaction of CI with CH3B1- over buffer gas pressures from 300-1100 Torr at 125 °C by ion mobility spectrometry (IMS).72 The experiments indicate that this reaction is not moved onto its high-pressure limit of kinetic behaviour by the use of buffer gas pressures near 1 atm. The same authors have carried out a similar study of the reaction of CI with isopropyl bromide at 640 Torr and 20-175 °C.73 It was concluded that under these conditions the reaction occurs primarily by a distinctly two-step mechanism ... 

Ion mobility spectrometry (IMS) is an instrumental method where sample vapors are ionized and gaseous ions derived from a sample are characterized for speed of movement as a swarm in an electric field [1], The steps for both ion formation and ion characterization occur in most analytical mobility spectrometers at ambient pressure in a purified air atmosphere, and one attraction of this method is the simplicity of instrumentation without vacuum systems as found in mass spectrometers. Another attraction with this method is the chemical information gleaned from an IMS measurement including quantitative information, often with low limits of detection [2 1], and structural information or classification by chemical family [5,6], Much of the value with a mobility spectrometer is the selectivity of response that is associated with gas-phase chemical reactions in air at ambient pressure where substance can be preferentially ionized and detected while matrix interferences can be eliminated or suppressed. In 2004, over 20000 IMS-based analyzers such as those shown in Fig. 1 are placed at airports and other sensitive locations worldwide as commercially available instruments for the determination of explosives at trace concentration [7],... 

Fig. 1. Two commercial ion mobility spectrometry (IMS) explosive detectors used at airports worldwide the Itemiser3 (GE Ion Track, (GE Security, Wilmington, MA, USA)) and the IONSCAN (Smiths Detection...

The trace detection portal manufactured and marketed by General Electric (GE) Security is called the EntryScan3 [34], shown in Fig. 4. This portal was the result of a collaborative development effort between Ion Track Instruments (ITI), which was later acquired by GE, and Pennsylvania State University (Penn State), funded by the TSL [4,5,23,32], The detection method used in this portal is ion mobility spectrometry (IMS) [35], GE utilizes their patented Ion Trap Mobility Spectrometer (ITMS) for detection [36],... 

We have shown that combining ion mobility spectrometry (IMS) equipment with mass spectrometry (MS) provides a powerful tool to examine the three-dimensional structure of polyatomic ions by measuring collision cross sections of mass identified ions. The technique is particularly useful in conjunction with molecular modeling or electronic structure calculations. Further, we have reviewed applications where the IMS-MS equipment is used to obtain kinetic and thermo chemical data of ions. 

Ion mobility spectrometry (IMS) is often coupled with GC and applied for VOC analysis. IMS identifies chemical substances based on their ion speed in the gas phase. These ions drift under the influence of applied voltage (100-350 V/cm) [131]. The detector combines the low cost of a single analysis with the short time necessary to obtain a measurement result (20-50 ms) and a low detection limit for... 

An important tool in the study of protein conformation and noncovalent protein complexes is the on-line combination of ion-mobility spectrometry (IMS) and MS. The IMS-MS instruments consists of an ESI source with related ion optics, a drift tube, and a mass spectrometer [75-76]. Quadrapole and TOF-MS instruments have been applied most frequently. In an IMS instrument, ions drift through a buffer gas under the iirfluence of a weak uniform electric field. The IMS separation of ions is based on differential mobility of ions related to shape and charge state. Within a particular charge state, compact ions show a higher mobility than more extended structures, because they experience fewer collisions. In this way, conformation differences between ions can be discovered. Compact ions have a smaller collision cross section. 

Ion mobility spectrometry (IMS), in which ions are separated on the basis of differences in the cross-sectional areas, can be used to determine the conformation and folding—unfolding kinetics of proteins.151,152 The basic idea behind these measurements is that because of their distinct shapes, different conformers will travel at... 

Baumbach et al. were the first to show that IMS can be used to quantify MTBE with ion mobility spectrometry (IMS) both in gasoline and in aqueous samples [67]. They coupled the IMS with a 25-cm multi-capillary column (MCC) in order to separate BTEX compounds and MTBE. Sensitivity depended very much on the ionization source used (see Table 7). Aqueous samples were introduced into the MCC by a membrane inlet but no further enrichment step has been applied. 

Ion Mobility Spectrometry (IMS) technology is used to detect nerve, vesicant, and blood agents. The Chemical Agent Monitor (CAM) uses ion mobility spectrometry to provide a portable, hand-held point detection instrument for monitoring nerve or vesicant agent vapors. Minimum levels detectable are about 100 times the acceptable exposure limit (AEL) for the nerve agents and about 50 times the AEL for vesicants. This insensitivity to low concentrations limits the utility of this instrument to check the efficacy of decontamination efforts or in occupational exposure measurements. 

Ion Mobiuty Spectrometry Ion mobility spectrometry (IMS) has been known for more than 25 years. In IMS, the analyte and impurity molecules... 

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