Abstract: A gas chromatographic method for the simultaneous determination of paracetamol (PAR), caffeine (CAF), diphenhydramine hydrochloride (DPH) and ephedrine hydrochloride (EPD) in Compound Paracetamol and Diphenhydramine Tablets has been developed. The separation of several components was achieved on a wide bore capillary column HP-1 (10 m×0.53 mm, 2.65 μm) with flame ionization detector (FID), and with pentadecane as internal standard, at a column temperature of 190 ℃. The linear ranges of detection for PAR, CAF, DPH and EPD were found to be 50-2400, 10-500, 10-500 and 10-500 mg/L, respectively. The detection limits were 1-30 μg/L, the average recoveries were 98.5%-101.1%. For intra-day assay, the relative standard deviations were less than 2.2%. The method has been applied successfully to the determination of fourfold mixture of PAR, CAF, DPH and EPD in pharmaceutical preparations. The developed method is rapid and sensitive and therefore provides a scientific basis for the quality control of Compound Paracetamol and Diphenhydramine Tablets.

Key words: caffeine, Compound Paracetamol and Diphenhydramine Tablets , diphenhydramine hydrochloride, ephedrine hydrochloride, paracetamol, wide bore capillary gas chromatography