Simultaneous determination of diclofenac potassium and methocarbamol in ternary mixture with guaifenesin by reversed phase liquid chromatography

New, simple, rapid and precise reversed phase liquid chromatographic (RP-LC) method has been developed for the simultaneous determination of diclofenac potassium (DP) and methocarbamol (MT) in ternary mixture with guaifenesin (GF), degradation product of methocarbamol. Chromatographic separation was achieved on a Symmetry® Waters C18 column (150 mm × 4.6 mm, 5 μm). Gradient elution based on phosphate buffer pH (8)-acetonitrile at a flow rate of 1 mL min−1 was applied. The UV detector was operated at 282 nm for DP and 274 nm for MT and GF. Linearity, accuracy and precision were found to be acceptable over the concentration ranges of 0.05–16, 0.5–160 and 0.5–160 μg mL−1 for DP, MT and GF, respectively. The optimized method proved to be specific, robust and accurate for the quality control of the cited drugs in pharmaceutical preparation.