Electrical mobility spectrometer

Figure 5. Transients observed in the concentrations of ultrafine particles in smog chamber studies of the photooxidation of dimethyl disulfide. Particles were measured with the electrical mobility spectrometer operating at fixed analyzer column voltages for the 11- and 20-nm sizes and with the differential mobility analyzer similarly operated for the 50-nm particles. (Reproduced from reference 49. Copyright 1991 American Chemical Society.)...

More dramatic improvements are obtained with the scanning electrical mobility spectrometer, which achieves better time resolution without sacrificing size resolution. 

Wang S. C., Flagan R. C. Scanning Electrical Mobility Spectrometer. Aero. Sci. Technol. 1990,13, 230-240. 

Note DMS differential mobility spectrometer, SMPS scanning mobility particle sizer, CPC condensation particle counter, TDMPS twin differential mobility particle sizer, DMPS differential mobility particle sizer, OPC optical particle counter, APS aerodynamic particle sizer, MAS mass aerosol spectrometer, LAS-X optical laser aerosol spectrometer, ELPI electrical low pressure impactor... 

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. 6. Schematic of a differential mobility spectrometer showing the principles of ion separation in a differential mobility spectrometry (DMS) drift tube. Ion paths are governed by both the asymmetric electric field and field dependence of mobility for an ion. The inset displays the asymmetric waveform of separation electric field used in the DMS drift tube. The waveforms shown are theoretical (top part) and actual or experimental (bottom part) used in these experiments.

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],... 

Tuch et. al. [231] ran a Mobile Aerosol Spectrometer (0.1 to 2.5 pm) and an Electrical Aerosol Spectrometer (0.5 to 10 pm) side by side for 6 weeks and found both to be reliable with almost identical results. Total number counts agreed with results from a Condensation Particle Counter. 

The first part of this chapter is a brief presentation of the interactions encountered by an ion that is moving through a neutral gas under the influence of a weak electric field. This simplified treatment pertains mainly to the classic form of linear ion mobility spectrometers (IMSs) and aspiration IMS devices. The motion of ions in other ion mobility devices, like the differential mobility spectrometer (DMS) and traveling wave (TW) IMS is also discussed. In the second part of the chapter, the implications on ion behavior in these embodiments of IMSs are discussed. The effects of the experimental parameters temperature, drift gas composition, moisture level of the supporting atmosphere, and concentration of the analytes are described in Chapter 11. 

DIFFERENTIAL MOBILITY SPECTROMETER AND THE DEPENDENCE OF ION MOBILITY ON THE ELECTRIC FIELD STRENGTH... 

Guevremont, R., Purves, R.W., Atmospheric pressure ion focusing in a high-field asymmetric waveform ion mobility spectrometer. Rev. Set Instrum. 1999, 70, 1370. Kudryavtsev, A., Makas, A., Ion focusing in an ion mobiUty increment spectrometer (IMIS) with non-uniform electric fields fundamental considerations. Int. J. Ion Mobility... 

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