NONAQUEOUS CAPILLARY ELECTROPHORESIS - APPLICATION TO THE SEPARATION OF COMPLEX-MIXTURES OF ORGANIC-ACIDS BY ION-PAIRING MECHANISM

Separation of a ten-membered model mixture of aromatic compounds posse ssing a carboxylic moiety along with other functional groups was inves tigated in the pH range 4.5-8.5, Methanol-acetonitrile (1:1) containin g 10 mmol/l sodium acetate and an equal concentration of Tris was used as the background electrolyte. It was demonstrated that within the mo del set three categories of acids were present, namely those which mov ed nearby the endoosmotic flow (on the anodic side) and increased slow ly their anodic mobility with the increasing apparent pH (1), those wh ich revealed a strong increase with increasing pH and could be best di scerned at apparent pH 7-7.5 in the negative operation mode (2) and th ose (a single member only) which possessed a strong anodic mobility ev en at low pH values and could be revealed within reasonable time in th e negative operational mode only (3). The mobility of the latter was o nly slightly affected by the pH change of the background electrolyte. Further addition of hydrophobic moiety possessing ion pairing reagents (typically trimethyloctadecyl ammonium bromide) helped to refine the resolution at neutral pH. The results demonstrate clearly the wide dif ferences in selectivity that it is possible to obtain by running elect rophoretic separations in nonaqueous buffers. (C) 1998 Elsevier Scienc e Ireland Ltd.