POTENTIALITIES OF ELECTROCHEMICAL DETECTION IN CONJUNCTION WITH NONAQUEOUS CAPILLARY-ELECTROPHORESIS

Electrochemical detection (ED) is applied to non-aqueous capillary ele ctrophoresis (CE) performed in an acetonitrile buffer. The detection i s based on a platinum microdisc electrode (d(Pt) = 25 mu m) placed clo se to the capillary outlet of a 75 mu m I.D. capillary. The CE-ED meas urements can be performed without using an electrical-field decoupler owing to the reduced effect of the high voltage on the detection circu it when using the present detector configuration and non-aqueous separ ation buffers. The ED system is studied performing hydrodynamic voltam metry in the presence of electroosmotic flow. The exponent of flow rat e dependence of the amperometric response is 0.68 for the present dete ctor configuration. Practical applications of non-aqueous CE-ED concer ning the analysis of dye substances such as malachite green, crystal v iolet, methylene blue, rhodamine B and morin are presented. In additio n, some pharmaceutically relevant compounds are studied by CE-ED. In p articular the capability of non-aqueous CE-ED for purity testing is di scussed. By analyzing a 2 mM solution of trimethoprim it is possible t o determine a content of 0.001% (2 x 10(-8) M) 4-methylamino-5-(3,4,5- trimethoxybenzyl)pyrimidine which is a possible impurity of trimethopr im. No effects of electrode fouling were encountered during CE-ED expe riments over measuring periods of several hours. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.