Simultaneous determination of some antibacterial drugs in Isosensitest broth using high-performance liquid chromatography with solid-phase extraction

A method is described for the simultaneous determination of combinations of some antibacterial drugs in a matrix of isosensitest broth. A double solid-phase extraction procedure is described in which trimethoprim and dibromopropamidine isethionate together with 4-chlorophenylbiguanide as internal standard are freed from endogenous components by a cation-exchange extraction cartridge and subsequently removed and individually separated by reversed-phase ion-pair chromatography. Sulfadiazine, sulfamerazine and p-aminobenzoic acid, unretained by ion exchange, are similarly isolated for chromatography by adsorption on a CH-bonded phase cartridge and individually assayed using the same chromatographic system. The rationale of the pre-treatment and chromatography is described and the quantitative aspects of the analyses of selected combinations of these drugs are reported.