Technical data

24 Agilent 6200 Series TOF and 6500 Series Q-TOF LC/MS System Concepts Guide

1Overview

Atmospheric pressure photoionization (APPI)

With the APPI technique, LC eluent passes through a nebulizing

needle to create a fine spray. This spray is passed through a

heated ceramic tube, where the droplets are fully vaporized.

The resulting gas/vapor mixture passes through the photon

beam of a krypton lamp to ionize the sample molecules

(Figure 5). The sample ions are then introduced into the

capillary.

APPI and APCI are similar, with APPI substituting a lamp for

the corona needle for ionization. APPI often also uses an

additional solvent or mobile phase modifier, called a “dopant”,

to assist with the photoionization process.

APPI is applicable to many of the same compounds that are

typically analyzed by APCI. APPI has proven particularly

valuable for analysis of nonpolar compounds.

Figure 5 Atmospheric pressure photoionization (APPI) source

HPLC inlet

nebulizer (sprayer)

drying gas

capillary

vaporizer

(heater)

UV lamp