The Ion Mobility Spectrum

The ion mobility spectrum in Figure 22-16b is a graph of detector response versus electrophoretic terms, see problem 26-46. drift time for several explosives. Peak area is proportional to the number of ions. Peaks are... 

Fig. 9.12 Decrease of the signal (peak area) of the specific peak considered in the ion mobility spectrum of a patient suffering angina lateralis during drug delivery (amoxicillin) for 3 days.

Here, approximately 2 parts per billion by volume of dimethyl sulfoxide (DMSO) in dry air were introduced continually and directly to the ionization region of the first atmospheric pressure IMS. The abscissa of the ion mobility spectrum is the arrival time of each ion species in milliseconds. This arrival time is inversely proportional to the mobility of the ion species represented by the individual peaks in the spectrum. 

The ion mobility spectrum has many forms that share one common feature The ion current intensity is measured as a function of an ion s mobility in a gas. As with other types of spectrometry, the ion mobility spectrum is obtained by correlating a change in a spectrometer s parameter with a physical property of the ions. In light spectrometry, the number of photons is recorded as a function of photon energy in mass spectrometry, the number of ions is recorded as a function of mass, and in ion mobility spectrometry (MS), the number of ions is recorded as a function of an ion s collision cross section, which is related to its mobility. The type of IMS depends on the instrumental parameter that is scanned to produce the intensity versus mobility spectrum. To understand the many types of mobility spectra, we must first consider the relation among mobility, electric field, and pressure. 

For the ion mobility spectrum shown in Figure 8.7, the ion produced from meth-amphetamine had an arrival time of 24.94 ms and a peak width at half height of 0.154 ms. Thus, the resolving power for this DTIMS was 24.94/0.154 = 161. 

There are two approaches that may be taken to follow the course of an ion/molecule reaction occurring in an ion mobility spectrometer. The first is through the profile of the ion mobility spectrum alone, and the second is from mass spectral ion intensities. 

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