Evaluation of a dual electrospray ionization atmospheric pressure chemical ionization source at low flow rates (∼50 μL/min) for the analysis of both highly and weakly polar compounds

The atmospheric pressure ionization (API) source for a commercial mass spectrometer was modified to operate as a dual source in both the electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) techniques by simultaneously utilizing the electrospray probe and the corona discharge needle. A switching box was designed to operate in either manual or programmable modes to permit rapid switching between ionization techniques without changing sources, probes, or breaking vacuum. The source can be operated using the following ionization techniques: ESI only, APCI only, ESI/APCI simultaneously, and ESI/APCI alternatingly. The optimum operating conditions for these ionization techniques were similar to the manufacturer's original specifications except that the APCI flow rate was lower (similar to 50 mu L/min versus 1000 mu L/min) and externally heated nebulizing gas was found to be desirable. A four-component mixture, introduced by flow injection was used to demonstrate the versatility of the dual ESI/APCI source. (J Am Soc Mass Spectrom 1998, 9, 1196-1203) (C) 1998 American Society for Mass Spectrometry.