CAPILLARY ELECTROPHORETIC SEPARATION OF ACIDIC AND BASIC-PROTEINS IN THE PRESENCE OF CATIONIC AND ANIONIC FLUOROSURFACTANTS

We report the use of mixtures of cationic and anionic fluorosurfactant s as additives for free-flow capillary electrophoresis of proteins. Ef fective deactivation of the capillary wall is obtained, which allows t he use of raw fused-silica capillaries. The magnitude and direction of the electroosmotic flow is strongly affected by the composition of th e surfactant mixture, and a suggested model for this behaviour in term s of micellation and formation of admicellar surfactant layers is desc ribed. By utilizing mixtures of the oppositely charged surfactants, it is possible to separate both positively and negatively charged protei ns in the same run. Due to charge interactions of the fluorosurfactant s with the proteins, it is possible to tune the separation selectivity , without having to change the buffer strength or pH. This was demonst rated in particular for the model substances myoglobin and ribonucleas e, where the order of elution could be reversed compared to their elut ion order in a normal buffer system. Another advantage of the fluorosu rfactant additives is their effectiveness in low concentrations (<100 mu g/ml) even when buffers of low ion strength are employed. Thus, rap id separations at a high field strength can be accomplished, without s uffering from excessive Joule heating. This is demonstrated with an ex ample, where a mixture of positively and negatively charged proteins i s separated in less then 2 min in a 10 mM phosphate buffer at pH 7.