PNNL

Abstract

Changes in liquid composition during gradient elution liquid chromatography (LC) and mass spectrometry (MS) analyses affect the electrospray operation. To establish methodologies for judicious selection of the electrospray voltage, we monitored in real-time the effect of the LC gradient on the spray current. The optimum range of the electrospray voltage shifted to lower values as the concentration of organic solvent in the eluent increased during reversed-phase LC analyses. These results provided the means to rationally select the voltage that ensured successful electrospray operation throughout gradient elution LC-MS experiments. A small run-to-run drift in the spray current was observed for electrosprays operated at constant voltage. This could be the result of fouling or degradation of the electrospray emitter, which affected the electric field driving the electrospray. Algorithms using feedback from spray current measurements to maintain the electrospray voltage within the optimum operating range throughout gradient elution LC-MS were evaluated. The electrospray operation with voltage regulation and at constant, judiciously selected voltage during gradient elution LC-MS measurements produced data with similar reproducibility.