Reagent gases, for chemical ionization

D.F. Hunt, Reagent gases for chemical ionization mass spectrometry, Adv. Mass Spectrom., 6 (1974) 517-522. 

Reagent Gases for Chemical Ionization Mass Spectrometry... 

REAGENT GASES FOR CHEMICAL IONIZATION MASS SPECTROMETRY... 

Important stereochemical results may be obtained using chemical ionization with chiral reagent gases. For example enantiomeric a-amino acids may be distinguished by Cl with optically pure 2-methylbutanol [17]. 

Measurement of the ratio of concentrations of each cannabinoid and its deuterated analog is achieved using chemical ionization and the technique of selected ion monitoring as previously described. Because of the low carrier gas flow rate used for capillary columns, we can use virtually any carrier gas we want (helium, hydrogen, etc.) and simply introduce our reagent gas or gases into the ion course via the make-up gas inlet. 

Selected ion flow tube mass spectrometry (SIFT-MS) is an analytical technique used for direct and quantitative determination of VOCs in mixtures of gases. SIFT-MS was introduced in 1976 by N. G. Adams and D. Smith. The technique can be applied for parallel real-time monitoring of a few substances [126]. A scheme of the SIFT-MS system is presented in Fig. 14.9 [127]. The principle of gas mixture analysis is based on the reaction of reagent ions with molecules of analyte within a specific time (a few milliseconds). In this method, chemical ionization is applied reagent ions are generated in the ion source by a suitable ionization gas (nitrogen, oxygen, or water vapor). Of aU the obtained ions, only cations of the desired m/z... 

The mass spectrometers utilized to date in this laboratory are conventional quadrupole mass spectrometers with two stages of pumping. Both electron impact (El) and chemical ionization (Cl) ion sources have been evaluated for SFC detection. The instrumentation illustrated in Figure 5 allows axial injection of the SFC effluent, although this is not an important parameter, and different designs are used in another instrument (6-8,12,13). Methane, isobutane or ammonia are the most frequent used Cl reagent gases. 

For the PAHs, however, Simonsick and Hites [50] showed that special chemical ionization reagent gases could be used so that isomers wiU appear to have different fragmentation patterns. They used methane as the reagent and then used the M/... 

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