Atmospheric pressure chemical source-analyzer interfaces

In atmospheric pressure chemical ionization (APCI) ion-molecule reactions occurring at atmospheric pressure are employed to generate the ions, i.e., it represents a high-pressure version of conventional chemical ionization (Cl, Chap. 7). The Cl plasma is maintained by a corona discharge between a needle and the spray chamber serving as the counter electrode. The ions are transferred into the mass analyzer by use of the same type of vacuum interface as employed in ESI. Therefore, ESI ion sources can easily be switched to APCI instead of an ESI sprayer, a unit comprising a heated pneumatic nebulizer and the spray chamber with the needle electrode are put in front of the orifice, while the atmospheric pressure-to-vacuum interface remains unchanged. [48,138]... 

Mass spectrometric detector selectivity provides imequivocal identification of target compoimds. By targeting the MW and by using specific software, fully automated peak recognition is possible. Compoimds need to be efficiently ionized for their detection. The single-quadmpole Waters ZQ is equipped with the two commonly available ionization sources electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). As most of the compounds to be examined were basic, electrospray with positive ionization was our method of choice. The selection of E SI was supported by previous experience gained over the last three years in our laboratory about 96% of the identified compounds, corresponding to more than 9,000 different molecules, were successfully analyzed with the ESI interface. 

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