The APCI spray insert includes the sheath gas and auxiliary gas plumbing, a needle insert, and a nozzle. Sample and solvent enter the nozzle through the needle insert, which is a metal electrospray capillary that extends from the sample inlet to a position that is 1 mm (0.04 in.) past the end of the nozzle.
The following figure shows the APCI spray insert with a magnified view of the nozzle.
The following figure shows the APCI needle insert removed from the APCI spray insert.
The APCI spray insert sprays the sample solution into a fine mist of charged droplets that enters the APCI vaporizer tube, which is ceramic and heated by the heater assembly. The vaporizer tube vaporizes the mist droplets at temperatures of up to 650 °C (typically 350–450 °C for flow rates of 0.1–2 mL/min). The APCI spray insert delivers the sheath gas and auxiliary gas to the nozzle. The flow of the nitrogen sheath and auxiliary gases move the sample vapor toward the corona discharge needle.
During APCI operation, the tip of the corona discharge needle, which is mounted inside the API source housing, is positioned near the vaporizer. The MS applies a high APCI corona discharge voltage (typically ±3 to ±5 kV) to the corona discharge needle to produce a steady APCI corona discharge current of up to 100 μA (typically 5 μA). The corona discharge from the needle produces reagent ion plasma primarily from the solvent vapor. Reactions of ions and molecules with the reagent ions in the plasma ionize the sample vapor.
The APCI source can accommodate liquid flows of 100 μL/min to 2 mL/min without splitting.
For information about the gases, see Sheath Gas, Auxiliary gas, and Sweep gas.