Electrochemical detection (ED) is applied to non-aqueous capillary electrophoresis (CE) performed in an acetonitrile buffer. The detection is based on a platinum microdisc electrode (d(Pt) = 25 mu m) placed close to the capillary outlet of a 75 mu m I.D. capillary. The CE-ED measurements can be performed without using an electrical-field decoupler owing to the reduced effect of the high voltage on the detection circuit when using the present detector configuration and non-aqueous separation buffers. The ED system is studied performing hydrodynamic voltammetry in the presence of electroosmotic flow. The exponent of flow rate dependence of the amperometric response is 0.68 for the present detector configuration. Practical applications of non-aqueous CE-ED concerning the analysis of dye substances such as malachite green, crystal violet, methylene blue, rhodamine B and morin are presented. In addition, some pharmaceutically relevant compounds are studied by CE-ED. In particular the capability of non-aqueous CE-ED for purity testing is discussed. By analyzing a 2 mM solution of trimethoprim it is possible to determine a content of 0.001% (2 x 10(-8) M) 2-amino-4-methylamino-5-(3,4,5-trimethoxybenzyl)pyrimidine which is a possible impurity of trimethoprim. No effects of electrode fouling were encountered during CE-ED experiments over measuring periods of several hours.