COMPARISON OF DIFFERENT ELECTROOSMOTIC FLOW MODIFIERS IN THE ANALYSISOF INORGANIC ANIONS BY CAPILLARY ELECTROPHORESIS

The determination of inorganic anions using capillary electrophoresis with non-treated silica capillaries requires reversal or elimination o f the cathodic electroosmotic flow (EOF). The behaviour of different m onocharged [tetrabutylammonium (TEA), cetyltrimethylammonium (CTA) and tetradecyltrimethylammonium (TTA)] or multicharged [hexamethonium (HM ) and hexadimethrine (HDM)] alkylammonium quaternary ions as electroos motic flow modifiers has been compared. Indirect spectrophotometric de tection using chromate as carrier ion has been used. The effect of EOF modifiers and chromate concentration, pH and applied potential on the separation of bromide, chloride, nitrite, nitrate, sulfate and phosph ate has been studied. Optimal conditions for the separation of these a nions have been established and resolution has been compared. Reproduc ibility in areas (R.S.D. 1.8-8.5%) and in migration times (R.S.D. 2.3- 7.5%), and detection limits (200-1000 mu g l(-1)) were similar for all the EOF modifiers. For HDM very low concentrations, down to 0.0001%, can be used successfully.