Assay of acetylsalicylic acid and three of its metabolites in human plasma and urine using non-aqueous capillary electrophoresis with reversed electroosmotic flow.

The separation of acetylsalicylic acid and three of its metabolites--salicylic acid, salicyluric acid and gentisic acid--is demonstrated in a non-aqueous capillary electrophoresis system with reversed electroosmotic flow. Solvent mixtures of methanol and acetonitrile are used for the electrophoresis media and different electrolytes have been investigated. The flow is reversed by the addition of the polycation hexadimethrine bromide and thus a negative voltage is used. This system provides a fast and effective separation of the four analytes. The separation method was applied to the assay of acetylsalicylic acid and its major metabolites in plasma and urine and the limits of quantification for all of these compounds are about 5 microg ml(-1) in plasma and 25 microg ml(-1) in urine.