WALL ADSORPTION OF SMALL ANIONS IN CAPILLARY ZONE ELECTROPHORESIS INDUCED BY CATIONIC TRACE CONSTITUENTS OF THE BUFFER

Fe(III), present as a trace constituent in the buffer, induces wall adsorption of small anions in coated and uncoated fused-silica capillaries even in the ppb concentration range. For di- and tribasic benzoates, drastic adsorption effects were found when the carboxylate groups were in an ortho position, leading to severely tailing peaks and a lower reproducibility of migration times. Benzoates with carboxylate groups in 1,3- or 1,4-positions were less affected than the ortho derivatives. The adsorption of the anions is related to Fe(III) attached to the capillary wall.