Simultaneous determination of five antibiotics by ion-pair high-performance liquid chromatography

This paper presents new information on the isocratic assay of five antibiotics thereby condensing five different assay procedures to one single report. Five antibiotics, viz., cephalexin and cefaclor (cephalosporins), isoniazid and pyrazinamide (anti-tubercular drugs) and minocycline (tetracycline series) have been separated and estimated from mixtures using a mobile phase consisting of tetrabutylammonium hydrogensulphate (0.025 M), methanol-acetonitrile (96:2:2) with pH adjusted to 3.0 with triethylamine. Column used was a Metaphase-CrestPak-ODS (250x4.0 mm, 5 mu m), with a flow-rate of 1.5 ml min(-1), with detection at 248 nm. The retention order was isoniazid (2.68 min), minocycline (5.79 min), pyrazinamide (6.89 min), cephalexin (8.50 min) and cefaclor (12.18 min). The composition and polarity of the mobile phase was found to be critical, not for individual drugs, but for mixtures. The linear dynamic range was 0.30-10.00 mu g ml(-1). Any one of the drugs could be used as internal standard for the other four drugs. All the drugs gave sharp, well-resolved peaks with optimum chromatographic figures of merit. Analytical performance parameters were calculated and were found to conform to the USP standards. (C) 1998 Elsevier Science B.V. All rights reserved.