DETERMINATION OF BENZOCAINE, DEXTROMETHORPHAN AND CETYLPYRIDINIUM ION BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH UV DETECTION

A high-performance liquid chromatographic method for the determination of benzocaine, cetylpyridinium ion and dextromethorphan based on the use of an end-capped Ultrabase C18 column and an ion-pair formation reaction in a water chloroform-methanol (10:50:40, v/v/v) mobile phase containing dioctyl sulphosuccinate is proposed. The use of a conventional or diode-array spectrophotometer resulted in calibration graphs with very different features. The determination ranges for benzocaine, cetylpyridinium and dextromethorphan provided by the diode-array detector were 10-100, 250-2000 and 250-2000-mu-g/ml, respectively, with relative standard deviations smaller than 3.0% for peak-height measurements and less than 1.40% for peak-area measurements. The conventional detector provided poorer results as a compromise wavelength must be chosen for measurements. The method was applied to the resolution of mixtures of the three analytes in pharmaceutical tablets. No interferences from other components of the tablets such as sorbitol, mint flavour and magnesium stearate were observed.