Quantitative measurements of small molecule mixtures using laser electrospray mass spectrometry

Quantitative measurements of atenolol, tioconazole, tetraethylammonium bromide, and tetrabutylammonium iodide using laser electrospray mass spectrometry (LEMS) reveal monotonic signal response as a function of concentration for single analytes, two- and four-component equimolar mixtures, and two-component variable molarity mixtures. LEMS analyses of single analytes as a function of concentration were linear over ~2.5 orders of magnitude for all four analytes and displayed no sign of saturation. Corresponding electrospray ionization (ESI) measurements displayed a nonmonotonic increase as saturation occurred at higher concentrations. In contrast to the LEMS experiments, the intensity ratios from control experiments using conventional ESI-MS deviated from expected values for the equimolar mixture measurements due to ion suppression of less surface active analytes, particularly in the analysis of the four-component mixture. In the analyses of two-component nonequimolar mixtures, both techniques were able to determine the concentration ratios after adjustment with response factors although conventional ESI-MS was subject to a greater degree of saturation and ion suppression at higher analyte concentrations.