Reversed-Phase High-Performance Liquid Chromatography and High-Performance Thin-layer Liquid Chromatography Methods for Simultaneous Determination of Theophylline, Guaifenesin and Guaifenesin Impurity (Guaiacol) in Their Bulk Powders and in Dosage Form

Two simple, rapid chromatographic methods were developed for the simultaneous determination of Theophylline (THP), Guaifenesin (GUI) and Guaifenesin impurity namely Guaiacol (GUA). The first method is an isocratic reversed-phase high-performance liquid chromatography (RP-HPLC) method, where separation of THP, GUI and GUA was achieved on C-18 column using methanol: water (containing 0.1% triethylamine): acetonitrile (30:60:10, by volume) as a mobile phase with a flow rate of 0.7 mL/min and UV detection at 275 nm. The separation was achieved at retention times (R-t 3.76, 6.76 and 8.79 for THP, GUI and GUA, respectively). The calibration plots were linear over the concentration range of 2-25, 2-37 and 0.5-10 mu g/mL for THP, GUI and GUA, respectively. The second method is high pressure thin layer liquid chromatography method, which was developed using silica gel plates 60F(254) as a stationary phase with ethyl acetate: hexane: methanol: ammonia (65:35:10:2, by volume) as a developing system. The densitometric measurements were performed at 275 nm with good R-f values (0.13, 0.35 and 0.8) for THP, GUI and GUA, respectively. The calibration plots showed good correlation over the range (0.4-2 mu g/band) for both THP and GUI, and (0.4-1.2 mu g/band) for GUA. The two proposed methods were validated according to ICH guidelines. The results for the two methods were statistically compared to those obtained by a reported high-performance liquid chromatography method and no significant difference was found regarding accuracy and precision.