THE EFFECTS OF STEARYL AND CETYL ALCOHOL ON THE ELECTROSPRAY MASS-SPECTROMETRY OF PROTEINS AND THEIR IMPLICATIONS ON THE ELECTROSPRAY MECHANISM

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 formatio n of a layer of the alcohol on its surface. If solvent evaporation fro m electrospray-generated droplets played a crucial role in the electro spray mechanism, the presence of a long-chained n-alkanol would interf ere with the gas-phase ion formation and cause a drastic decrease in a nalyte response. As it turned out, the electrospray responses of prote ins 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. The se results lend further support to our hypothesis that solvent evapora tion is not a necessary prerequisite to ion formation in electrospray, and that ions are formed early rather than late during the electrospr ay process; the earliest point that this can occur is at the Taylor co ne.