Influence of electrolyte composition on the effective electric field strength in capillary zone electrophoresis

In capillary zone electrophoresis the electrophoretic velocity of an ion decreases as the concentration of the background electrolyte solution is increased. This is caused by changes in the electrophoretic mobility of the ion (muep) as well as by changes in the net force affecting it, namely the effective electric field strength (Eeff). The electrophoretic mobility of an ion is altered through changes in absolute viscosity of the electrolyte solution and changes in the solvated size of the ion. Eeff is altered mainly by changes in the magnitude of the charge asymmetry effect and the electrophoretic effect, both of which retard the motion of ions. In this study, the three-marker technique was used to study the effect of background electrolyte concentration (0.02-0.08M 3-[cyclohexylamino]-1-propanesulfonic acid and counter ion (Li, Na, K, and Cs) on Eeff. It was found that the concentration of the background electrolyte markedly affects Eeff and that Eeff approaches E as the concentration of the background electrolyte approaches zero. The counter ion had a minor effect on Eeff: as the size of the hydrated radius of the counter ion increased, Eeff decreased. The three-marker technique proved to be efficient for such determinations.