The Reduction of Chemical Noise in an Atmospheric Pressure Ionization/Ionspray Interface for Mass Spectrometry

Abstract

The reduction of chemical noise and the consequent gain in sensitivity on an ionspray interface to an ion-trap mass spectrometer for capillary electrophoresis/mass spectrometry (CE/MS) applications is described. The principal sources of chemical noise were found in ionized airborne contaminants and in solvent cluster adducts. The reduction of these unwanted signals was achieved by the application of a cover to the heated-shield atmospheric pressure ionization interface and the removal of all plastic components near the heated zones. By the use of a clean bath gas and curtain gas, the ionization region was constantly purged with nitrogen gas to prevent the deposition of contaminants on the inside surfaces and to protect the orifice from obstruction. The cover of the heated-shield interface together with the presence of the bath and curtain gas also increased the desolvation of solvent clusters, most likely by the application of more concentrated heat during the ionization process.