A parametric investigation of an electrospray ion source and interface has been carried out with a focus on elemental analysis. The source and interface variables investigated were the curtain-gas flow rate and the voltage biases of the electrospray capillary tip, the front plate, the sampling plate, the skimmer, and the barrel ion extractor lens. The analytes studied (M+ and M++) included the alkali metals, the alkaline earth metals, and cobalt—all prepared in methanol (MeOH) solutions. The two most important interface parameters in terms of their effect on the nature of the resulting mass spectrum were the curtain-gas flow rate and the sampling-plate voltage bias. A minimum, but modest, flow rate of curtain gas was required in order to observe analyte ion signals, and, when combined with a low sampling-plate voltage, the observed signal species were primarily analyte ion–solvent clusters [M(MeOH) n+1 and M(MeOH) m+2]. As the values of these two parameters were increased, these species were declustered, plus-two analyte ions were reduced to plus-one species, and ultimately the mass spectra were dominated by the bare singly charged analyte ion (M+). Also, these two variables (curtain-gas flow rate and sampling-plate voltage) seem to act in a synergistic manner, with neither variable alone able to effect complete declustering and charge reduction.
Ion source surface processing based on glow discharge in supersonic cross gas flow control