Atmospheric pressure chemical ionization flow rate through

Atmospheric Pressure Chemical Ionization. As its name reveals, APCI[16] is a Cl carried out at atmospheric pressure instead of under vacuum, as occurs for classical Cl. As for ESI, the sample must be in a solution that is continuously flowing into the APCI source (flow rate between 0.2 and 2 ml min ). The solution passes through a pneumatic nebulizer and is desolvated in a heated quartz tube or heating block, thus producing vaporization of solvent and analyte molecules (Figure 2.4). 

Methods Ambient ionization methods, of which there are now over 20, e.g., desorption electrospray ionization (DESI), desorption atmospheric pressure chemical ionization (DAPC), desorption atmospheric pressme photo-ionization (DAPPI), and direct analysis in real time (DART), are now joined by paper spray, a method where ESI is initiated at the pointed tip of a piece of filter paper. A drop of blood ( 15 pi) is dried on the paper, and then the paper is moistened with 25 pi of a solvent suited to both the extraction of the analytes from the blood and the ESI process (e.g., 90% methanol 10% water with either 100 ppm acetic acid or 200 ppm sodium acetate). When the paper is exposed to high voltage (3-5 kV) while held close ( 5 mm) to the entrance of the mass analyzer, a spray (similar to electrospray) is induced at the tip of the paper as capillary action carries extracted compounds through the paper (Figure 4.5). The spray is maintained for 30-90 s at a flow rate comparable to that used in nano-electrospray. 

A number of interfaces such as thermospray (TSP), ionspray (IS), atmospheric chemical ionization (APCI) and electrospray (ES) can tolerate much higher flow rates without requiring that the flow be split at the end of the LC column. Ions that are produced in atmospheric pressure ionization sources are moved directly into the mass spectrometer through small apertures. 

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