Micellar liquid chromatographic determination of anti-convulsant drugs in pills and capsules

A simple chromatographic procedure is reported for the determination of several anti-convulsant drugs in pharmaceuticals: carbamazepine, and the benzodiazepines bentazepam, halazepam, oxazepam, pinazepam, and tetrazepam. The procedure utilizes a C-18 column, a hybrid micellar mobile phase of 0.1 M SDS-3% butanol-0.1% triethylamine-0.01 M phosphate buffer (pH 3), and UV detection (230 nm). The drugs eluted in less than 13 min, in accordance to their relative polarities, as indicated by their octanol-water partition coefficients. The limits of detection (mu g/mL), and intra and inter-day repeatabilities (%), for 4 mu g/mL were: carbamazepine (0.03, 1.0, 4.1), bentazepam (0.05, 1.3, 1.6), halazepam (0.10, 2.3, 1.3), oxazepam (0.02, 0.9, 7.9), pinazepam (0.01, 0.3, 5.1), and tetrazepam(0.03, 1.1, 6.3). The results were compared with those obtained in a conventional procedure using methanol-water 70:30 (v/v). The contents evaluated with the micellar mobile phase always agreed with the declared compositions, instead, with the aqueous-organic mobile phase, pinazepam gave poor recoveries and halazepam did not elute at appropriate times.