Addition of Reagent Gases, Dopants, and Shift Reagents

5 Addition of Reagent Gases, Dopants, and Shift Reagents 

FIGURE 11.2 Plots of drift times for ammonia, hydrazine (HZ), and monomethylhydrazine (MMH) with vapor levels of 5-nonanone in the drift gas ranging from trace levels (10 ppb or less) to 1.5 ppm. Although all ions undergo increases due to the formation of ion-neutral adducts, the ordering of drift time is by ion mass in relatively unmodified gas, and when vapor 

FIGURE 11.3 An example of the formation of adducts in drift tubes can be seen in mobility spectra from ESI-IM-MS analysis of a solution of a pharmaceutical, lamivudine miz 230), of PEG (mIz 635, n = 14), and for a lamivudine/PEG complex (mIz 864, n = 14) overlaid with normalized intensities. This example occurred with special efforts to modify the supporting atmosphere of an IMS drift tube and was attributed to clusters formed in the ESI spray. In this instance, the ion clnsters were strongly held and had lifetimes enough to pass through the IMS drift region. 

6 Multiple Reagent Gases to Simplify or Clarify Response 

Since drift tubes for mobility spectrometers can be comparatively inexpensive, several analyzers (CAMs) were used in parallel, each with a particular dopant, and operated continuously for ambient air monitoring. The dopants were water, acetone, and DMSO as used with GC-IMS analysis of a complex mixture of volatile organic compounds. The CAMs were not modified otherwise and were operated with positive ion polarity, in parallel, and without any chromatographic prefractionation of sample. Ambient air inside a university work site, the stockroom of the Department of Chemistry and Biochemistry at New Mexico State University, was sampled continuously for several hours before and during laboratory classes for undergraduate students when activity increases in the stockroom with dispensing materiel and chemicals. Each analyzer provided response from general to specific, based on 

---