Ion Sources for APCI

The ions are transferred into the mass analyzer by use of the same atmosphere-to-vacuum interface as employed in ESI. Therefore, ESI sources can easily be switched to APCI operation. To do so, the ESI spray head is exchanged for a unit comprising a pneumatic nebulizer and a heated spray chamber with a needle electrode mounted in front of the sampling orifice, while the atmospheie-to-vacuum interface stays in place (Fig. 12.40) [51,173]. Different from ESI, APCI requires high liquid flow (200-1000 pi min ) for effective vaporization. 

Note The significant enhancement of primary ion formation by a corona discharge as compared to a Ni source has been implemented in early API sources, a context in which a basic APCI process has already been described (Eqs. 12.1-12.6 in Chap. 12.1.1) [174,175]. The corona needle employed to expand the acceptance range of TSP basically represents an APCI m e for these sources, too [28]. 

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