New spectrophotometric methods applied to the simultaneous determination of diclofenac potassium and tizanidine

Simple, sensitive, and specific spectrophotometric methods were developed and validated for quantitation of diclofenac potassium and tizanidine in tablet dosage form. Three new analytical methods were developed based on the simultaneous estimation of drugs in a binary mixture without previous separation. In multiwavelength technique, the binary mixture was determined by mixed standards and three sampling wavelengths of 277 nm, 295 nm (isobestic point), and 320 nm. In simultaneous equation method, the drugs were determined by using the absorptivity values of diclofenac potassium and tizanidine at selected wavelengths, viz., 277 nm and 320.3 nm. The standard deviation value for the validation parameters was found to be between 0.08 and 0.68 for multiwavelength technique and between 0.069 and 1.23 for simultaneous equation method. The graphical absorbance ratio method was performed by absorbances at 277 nm, 295 nm (isobestic point), and 320.4 nm of their mixture. These three methods are simple, accurate, and rapid, and they require no preliminary separation and can therefore be used for routine analysis of both drugs in quality control laboratories.