Atmospheric-pressure chemical ionization

[5] The application of APCI with HPLC has gained a large popularity in trace analysis detection such as steroids, pesticides and also in pharmacology for drug metabolites.

[6] A typical APCI source usually consists of three main parts: a sample inlet, a corona discharge needle, and an ion transfer region under intermediate pressure.

If a fragment ion of a sample is observed, thermal degradation has taken place by the heated nebulizer interface, followed by the ionization of the decomposition products.

Instead, the ionization must occur using either corona discharges or β- particle emitters, which are both electron sources capable of handling the presence of corrosive or oxidizing gases.

[18] In the late 1970s an APCI mass spectrometer system (the TAGA, for Trace Atmospheric Gas Analyzer), mounted in a van for mobile operation, was introduced by SCIEX,[19][20] providing high sensitivity for monitoring polar organics in ambient air in real time.

In 1981 a triple quadrupole mass spectrometer version was produced, allowing real-time direct air monitoring by APCI-MS/MS.

A similar platform was used for the SCIEX AROMIC system (part of the CONDOR contraband detection system developed together with British Aerospace) for the detection of drugs, explosives and alcohol in shipping containers at border crossings, by sampling the interior airspace.

[21][22] In the mid-1980s and into the early 1990s, the advantages of performing LC/MS with APCI and with electrospray, both atmospheric pressure ionization techniques, began to capture the attention of the analytical community.

Additionally, APCI considerably reduces the thermal decomposition of the analyte because of the rapid desolvation and vaporization of the droplets in the initial stages of the ionization.

[24] Another advantage to using APCI over other ionization methods is that it allows for the high flow rates typical of standard bore HPLC (0.2–2.0 mL/min) to be used directly, often without diverting the larger fraction of volume to waste.

Because APCI involves a gas-phase chemistry, there is no need to use special conditions such as solvents, conductivity, pH for LC.