INVESTIGATIONS OF THE ELECTROSPRAY INTERFACE FOR LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

The positive Ions, produced by electrospray from solutions of various analytes In methanol, were detected with an atmospheric pressure triple quadrupole mass spectrometer. Analytes studied Included NH4+ Na+ K+, Cs+, Ca2+, and the onium Ions BH+ of some 30 organic nitrogen bases B. The analyte ion sensitivities decrease with analyte ion concentration and presence of foreign electrolyte in the solution, at concentrations above 10~5 mol/L. At low concentrations, sensitivities are very high such that ions at 10‒8 mol/L concentration can be easily detected. Detection limits in the subfemtomole to attomole range have been achieved. The sensitivity of the organic bases B is pH dependent and increases as the [BH+] in solution increases. However the effect is obscured by the depression of the ion signal caused by foreign electrolyte. It Is also shown that above 10‒5 mol/L B In solution, gaseous B at sufficient pressure can be generated and gas-phase proton transfer to higher gas phase basicity coanalytes can occur. Dimers, B2H+, may also be formed In the gas phase. The gas phase ion reaction time is estimated as ~2 ms. © 1990, American Chemical Society. All rights reserved.