Chemical ionization mass spectrometry characteristics

Kobayashi Y, Saiki K, Watanabe F. 1993. Characteristics of mass fragmentation of steroids by atmospheric pressure chemical ionization/mass spectrometry. Biol Pharm Bull 16 1175-1178. 

Pyrolysis-direct chemical ionization mass spectrometry ( r-DCI-MS) was recently introduced as a pyrolysis technique for the characterization of complex macromolecular samples and for the analysis of biopolymers. This technique does not require special pyrolysis equipment and can be performed with an instrument which is equipped with a chemical ionization source and a standard DCI probe, which consists of an extended wire used to introduce the sample material directly into the chemical ionization plasma. An important characteristic of this technique is the pyrolysis... 

Previously, spectral data for sotalol were reported using negative ion chemical ionization mass spectrometry (4). The base peak (M-79) corresponded to the loss of (-SO2CH3). Other characteristic ions were found at m/z 163 (C2F5COO)" m/z 147 (C2F5CO)" m/z 144 (C2F4COO)- and at (M-147)- and (M-166). ... 

Electron affinities of molecules are of interest not only in gas-phase reactions, e.g. in negative chemical ionization mass spectrometry, but also in the field of condensed-phase chemistry. It is characteristic that negative ions are by far not studied to the same level of detail as the corresponding positive ions. However, during the last decade a large number of EA determinations based on measurements of electron transfer equilibria utilizing pulsed high-pressure mass spectrometry have been reported . ... 

These distinguishing characteristics of chemical ionization mass spectrometry have been discussed previously, but as a result of recent studies (to be discussed in more detail later) we have come to recognize another characteristic aspect of the chemical ionization process when the high-pressure mass spectrometric technique is used. When chemical ionization is effected at a pressure in the mass spectrometer ionization chamber on the order of 1 Torr, the ions comprising the mass spectra are produced by collision processes, and after formation the ions undergo a number of collisions with molecules of reactant gas before they pass out of the ionization chamber. Thus, unlike the conditions which obtain in conventional (low-pressure) electron-impact and photon-impact ionization, the ions produced by chemical ionization are not isolated. That is to say, they are not formed... 

Clearly, small differences in ionic energies are here having a profound effect on the spectra produced, and it is one of the desirable characteristics of chemical ionization mass spectrometry that spectra are significantly affected by energy differences with magnitudes comparable to those of importance in condensed-phase phenomena. 

Carboxylic acids The smallest carboxylic acid, formic acid, can be measured using infrared spectroscopy (Table 11.2), since it has characteristic absorption bands. As discussed earlier and seen in Fig. 11.33b, mass spectrometry with chemical ionization using SiF5 also revealed HCOOH in an indoor environment (Huey et al., 1998). However, since the sensitivity in these initial studies was about two orders of magnitude less than that for HN03, the detection limit may be about the same as that for FTIR and TDLS. Formic and acetic acids have been monitored continuously from aircraft (Chapman et al., 1995) and their surface flux determined by eddy correlation (Shaw et al., 1998) using atmospheric pressure ionization mass spectrometry. Detection limits are about 30 ppt. 

Covey, T. 1995. Analytical characteristics of the electrospray ionization process. In Biochemical and Biotechnological Applications of Electrospray Ionization Mass Spectrometry, Snyder, A. P., ed., Washington, D.C. American Chemical Society, 619,21-59. 

HPLC on a 2.1mm column at 400 til min-1 flow. Two drugs are monitored by selected ion monitoring. Left 400 pi min-1 is injected in the source. Centre 132 almin-1 is split to the source. Right 15 pi min-1 is split to the source. The integration values are displayed on top of the peaks and show that at reduced flow rates the sensitivity is slightly increased. Reproduced with data from Covey T., Analytical Characteristics of the Electrspray Ionization Process pp. 21-59 in Biochemical and Biotechnological Applications of Eletrospray Ionization Mass Spectrometry Snyder A.P., ed., ACS Symposium Series 619, American Chemical Society, 1996. 

An internal standard should meet the following three requirements. First, it should have the same or very similar physical-chemical properties as the analyte, particularly hydrophobicity and ionization characteristics, so that it can mimic closely the performance of the analyte in every stage of analysis, i.e., from sample preparation, chromatographic separation, to mass spectrometric detection. In this way, any losses during sample preparation or variations in the mass spectrometry detection can be corrected. 

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