The effects of stearyl and cetyl alcohol on the electrospray mass spectrometry of proteins and their implications on the electrospray mechanism

Abstract

The presence of a low percentage of a long-chained n-alkanol, such as stearyl or cetyl alcohol, in a micrometer-size water droplet is known to retard significantly the droplet's evaporation rate due to formation of a layer of the alcohol on its surface. If solvent evaporation from electrospray-generated droplets played a crucial role in the electrospray mechanism, the presence of a long-chained n-alkanol would interfere with the gas-phase ion formation and cause a drastic decrease in analyte response. As it turned out, the electrospray responses of proteins tested with and without the presence of n-alkanols were comparable. In these experiments, the n-alkanols were added either as solutes in water/methanol solutions of proteins or in hexane solutions delivered coaxially to aqueous protein solutions during their electrospray. These results lend further support to our hypothesis that solvent evaporation is not a necessary prerequisite to ion formation in electrospray, and that ions are formed early rather than late during the electrospray process; the earliest point that this can occur is at the Taylor cone.