Simple, accurate and precise spectrophotometric and RP-HPLC methods were developed for simultaneous estimation of Diclofenac sodium and Chlorzoxazone in combined dosage form. In spectrophotometric method, methanol was used as solvent. Diclofenac sodium is treated with concentrated nitric acid. The reaction product was showing λmax at 360 nm. While Chlorzoxazone remains unreacted with nitric acid and showing λmax at 282 nm. The calibration curve is linear over the range of 4-12 μg /mL and 30-70 μg /mL, the LOD value were found to be 0.056 and 0.286 μg /mL, while LOQ value were found to be 0.170 and 0.866 μg /mL for Diclofenac sodium and Chlorzoxazone respectively. RP-HPLC method uses a Phenomenex C18, (250 mm × 4.6 mm × 5 μm) analytical column, mobile phase is Methanol:Water (70:30) pH 5.0 adjusted with Acetic acid was pumped at flow rate of 1 ml/min with UV detection at 282 nm. Retention time of Diclofenac sodium and Chlorzoxazone was 6.095±0.03 & 3.937±0.03, respectively with linearity range of 6-12 μg /mL and 30-70 μg /mL for Diclofenac sodium and Chlorzoxazone respectively. The LOD value were found to be 0.0033 and 0.0775 μg /mL, while LOQ value were found to be 0.01 and 0.235 μg / mL for Diclofenac sodium and Chlorzoxazone respectively.
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