Drug monitoring by a fully automated high-performance liquid chromatographic technique, involving direct injection of plasma.

A procedure involving direct injection of whole plasma for analyses of drugs by an automated high-performance liquid chromatograph was developed. This system comprised two columns, two pumps, one detector, two programmable switching valves, an automatic sample injector with a cooling device for sample tubes and a microprocessor. Effluents from the first column, containing a drug of interest, were selectively introduced into the second column for further separation. The columns used were an aqueous gel chromatography column (column 1) and an ODS column (column 2). The solvent for column 1 must be weaker than that for column 2, so that the solutes from the former will be enriched at the top of the latter. The validity and applicability of this procedure for the study of drug metabolism were demonstrated with the antibiotic cefmetazole, the anticoagulant warfarin, the antitumour agent carboquone and the anaesthetic ketamine.