EFFECT OF ORGANIC-SOLVENTS ON SOLUTE MIGRATION AND SEPARATION IN CAPILLARY ZONE ELECTROPHORESIS

The effect of organic modifiers on mobility and selectivity in capilla ry zone electrophoresis was investigated. Test solutes having differen t functionalities were electropherographed at acidic and neutral pH wi th aqueousorganic buffers. The results show that the electroosmotic mo bility is mainly influenced by buffer viscosity. The role of the diele ctric constant, zeta-potential and modifier-capillary wall interaction s, which may be significant at trace levels of organic modifier, is ve ry much diminished as the organic content is increased. Buffers having equivalent viscosities generate similar electroosmotic mobilities irr espective of the type and percentage of the organic modifier. Solute e lectrophoretic mobility is affected similarly because of the identical nature of the forces responsible for the electroosmotic and electroph oretic flow phenomena. However, solute electrophoretic mobility is als o influenced by the degree to which the organic modifier affects the e quilibrium that generates the electrophoretically-active solute ions. As a consequence, the order of elution of some solutes may change with increasing buffer organic content. The separation of weakly-hydrophil ic solutes is improved with increasing organic proportions. The separa tion of dipeptides first improved with the addition of up to 15 % ACN, then deteriorated with further increase of ACN proportion. An example showing change in migration order and peak cross-over is presented an d discussed.