Smart Spectrophotometric Methods for the Determination of Chlorzoxazone and Paracetamol Form Tablets

Abstract

Two simple, accurate and precise spectrophotometric methods have been introduced for the simultaneous measurement of chlorzoxazone and paracetamol in a combined tablet form. The first method is a graphical spectrophotometric method utilizes the data taken at multiple wavelengths to generate linear plots, from which the concentration of analytes can be determined, the second method is dual wavelength spectrophotometric method which is based on selecting two wavelengths for each drug to ensure that the absorbance difference is zero for the other drug. In the graphical method the absorbance was measured at 240, 260, 280 and 300 nm, while in the dual wavelength method; 224.5 nm and 264 nm were chosen for chlorzoxazone determination since paracetamol shows equal absorbance at these wavelengths. Conversely, for paracetamol determination, wavelengths 234.5 nm and 273.5 nm were selected, with chlorzoxazone having zero absorbance difference at these wavelengths. Both drugs adhere to Beer-Lambert’s law within a concentration range of 4–20 µg/mL. The methods accuracy and precision were assessed following the International Conference on Harmonization (ICH) guidelines. Recovery studies further validated the method's accuracy. The precision of the method was demonstrated by low relative standard deviations (% RSD) less than 2%, indicating good repeatability and intermediate precision. Method accuracy was confirmed by the agreement between the determined and actual contents, also with % RSD less than 2%. The two methods enable direct analysis of chlorzoxazone and paracetamol in commercially available tablet formulations without the need for prior separation.