Comparison of mu m and mm sized disk electrodes for end-column electrochemical detection in capillary electrophoresis

End-column electrochemical detection based on either the use of a 25 mu m m icrodisk electrode or a 0.5 mm macrodisk electrode has been compared with r espect to performance and influence on non-aqueous capillary electrophoreti c separations. Despite the much higher coulometric efficiency obtained with the larger disk electrode, the microdisk electrode configuration offers co mparable limits of detection (LOD) for the neutral and positively charged f errocene compounds employed in conjunction with a non-aqueous acetonitrile- based buffer. The LODs for ferrocene were found to be 4.0 x 10(-8) M and 6. 7 x 10(-8) M for the microdisk and macrodisk detector, respectively. In add ition, both detector arrangements showed different relative responses for n eutral and positively charged analytes. The macroelectrode-based detector i ntroduced additional zone broadening while this was not found to be the cas e with the microelectrode arrangement. Using the microelectrode detector, t he band broadening in an electro-osmotically driven flow system was compare d to that in a gravity flow-based system. It was demonstrated that the zone broadening under gravity flow conditions was approximately twice as large as under electro-osmotic flow conditions for a typical set of experimental parameters.