Simultaneous determination of paracetamol and methocarbamol in tablets by ratio spectra derivative spectrophotometry and LC

The application of the ratio spectra derivative spectrophotometry and high- performance liquid chromatography (HPLC) to the simultaneous determination of paracetamol (PAR) and methocarbamol (MET) in combined pharmaceutical tab lets is presented. The spectrophotometric procedure is based on the use of the first derivative of the ratio spectra obtained by dividing the absorbti on spectrum of the binary mixtures by a standard spectrum of one of the com pounds. The first derivative amplitudes were measured at 243.0 and 230.3 nm for the assay of PAR and MET, respectively. Calibration graphs were establ ished for 2-30 mug/ml for PAR and 2-36 mug/ml for MET in binary mixture. Th e detection limits for PAR and MET were found 0.097 and 0.079 mug/ml, respe ctively; while the quantification limits were 0.573 mug/ml for PAR and 1.71 7 mug/ml for MET. For the HPLC procedure, a reversed-phase column with a mo bile phase of methanol-water (60.40, v/v), was used to separate both compou nds with a detection of 274.0 nm. Linearity was obtained in the concentrati on range of 2-300 and 1.5-375 mug/ml for PAR and MET, respectively. The det ection and quantification limits were found to be 0.42 and 1.4 mug/ml for P AR and 0.36 and 1.2 mug/ml for MET, respectively. The relative standard dev iations were found to be less than 0.52%. indicating reasonable repeatibili ty of both methods. The proposed methods were successfully applied to the d etermination of these drugs in commercial tablets. (C) 2001 Elsevier Scienc e B.V. All rights reserved.