Effect of affinity for droplet surfaces on the fraction of analyte molecules charged during electrospray droplet fission

The effect of uneven fissioning of mass and charge from electrospray drople ts on the amount of analyte charged during the electrospray process was exp lored. A surface selectivity factor (S) was developed to describe the affin ity of an analyte for the droplet surface, and both theoretical and experim ental response curves were compared for analytes with various S values. The theoretical response curves were generated by calculating the overlap betw een the charge and analyte spawned from parent droplets to determine the am ount of analyte charged. This overlap was then graphed as a function of ana lyte concentration. Differences in the amount of analyte charged during dro plet fission were predicted for analytes of varying surface affinities. The issue of analyte partitioning between the surface and interior phases of t he ESI droplet was also included in the discussion. This was accomplished b y applying the equilibrium partitioning model to a set of offspring droplet s to determine the amount of analyte on their surfaces and then calculating the overlap between fissioning analyte and excess charge. Experimental res ponse curves resembled theoretical ones, and S values predicted from theory were in excellent agreement with those predicted on the basis of the struc tural characteristics of the analytes.