The instant invention deals with species that may be required to enhance an upstream sample preparation or separation process may be less compatible with the downstream ES processes and cause reduction in MS signal. New electrolytes have been found that increase positive and negative polarity analyte ion signal measured in ESMS analysis when compared with analyte ESMS signal achieved using more conventional electrolytes. The new electrolyte species increase ES MS signal when added directly to a sample solution or when added to a second solution flow in an electrospray membrane probe, it has also been found that running the ES membrane probe with specific electrolytes in the second solution of the ES membrane probe have been found to enhance ESMS signal compared to using the same electrolytes directly in the sample solution being electrosprayed. The new electrolytes can be added to a reagent ion source configured in a combination atmospheric pressure ion source to improve ionization efficiency.