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Abstract
A facile and accurate spectrophotometric method was developed for the simultaneous assay of ibuprofen (IBP) and methocarbamol (MTC) binary pharmaceutical mixture without prior tedious separation processes. The method was based on measuring the third and the fourth derivative amplitudes of each drug in presence of the other, using zero-crossing technique. The third derivative amplitudes were measured at 234.6 nm and at 226.8 nm for the simultaneous assay of MTC and IBP, respectively. On the other hand, the fourth derivative amplitude values were measured at 228 nm and at 233 nm for the simultaneous assay of MTC and IBP, respectively. The method was validated according to ICH guidelines. The linear calibration graphs were constructed over the concentration ranges of 3.0–30.0 and 5.0–50 μgmL-1 for MTC and IBP, respectively with sensitivities comparable to HPLC-UV methods. The detection limits of the third derivative measurements were 0.262 and 0.257 μgmL-1 for MTC and IBP, respectively, while for the fourth derivative measurements, the detection limits were 0.356 and 0.189 μgmL-1 for MTC and IBP, respectively. The proposed method was applied to assay the studied drugs in their pharmaceutical combined tablets. The results were efficiently compared to those obtained by the official USP reference methods.