EVALUATION OF A DUAL ELECTROSPRAY-IONIZATION ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION SOURCE AT LOW-FLOW RATES (SIMILAR-TO-50 MU-L MIN) FORTHE 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 ele ctrospray ionization (ESI) and atmospheric pressure chemical ionizatio n (APCI) techniques by simultaneously utilizing the electrospray probe and the corona discharge needle. A switching box was designed to oper ate in either manual or programmable modes to permit rapid switching b etween ionization techniques without changing sources, probes, or brea king vacuum. The source can be operated using the following ionization techniques: ESI only, APCI only, ESI/APCI simultaneously, and ESI/APC I 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 vers us 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 A m Soc Mass Spectrom 1998, 9, 1196-1203) (C) 1998 American Society for Mass Spectrometry.