EFFECT OF OPERATING PARAMETERS ON ANALYTE SIGNALS IN ELEMENTAL ELECTROSPRAY MASS-SPECTROMETRY

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-pas 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)(n)(+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 Bow rate and sampling-plate voltage) seem to act in a synergistic manner, with neither variable alone able to effect complete declustering and charge reduction.