Authors:Maha M. Abdelrahman, Nada S. Abdelwahab, Ahmed A. Taha, and John M. Boshra
The presented study was intended to design two validated, simple, and precise chromatographic methods for the determination of chlorzoxazone (CHZ) and diclofenac potassium (DIC) in the presence of chlorzoxazone nephrotoxic degradation product, 2-amino-4-chlorophenol (ACP) which was reported to be its main impurity. Reversed-phase high-performance liquid chromatography (RP-HPLC) was the first method where chromatographic separation was performed on ZORBAX Eclipse Plus C8 column using methanol—water—phosphoric acid (75:25:0.05, by volume) as the mobile phase at a flow rate of 1 mLmin−1. CHZ, DIC, and ACP retention times were found to be 4.26, 7.94, and 3.17, respectively, using photodiode array detector (DAD) at 230 nm. The calibration curves showed good linear relationships in the concentration ranges of 3–45 μg mL−1 for CHZ, 3–40 μg mL−1 for DIC, and 5–45 μg mL−1 for ACP. The second method was thin-layer chromatography (TLC) at which chromatographic separation was carried out on Merck TLC silica gel 60 F254 aluminum plates followed by measurement of separated bands at 230 nm and using chloroform—ethanol—triethylamine (9:1:0.1, by volume) as the developing system. The studied components were successfully separated with significantly different Rf values (CHZ, Rf = 0.63; DIC, Rf = 0.35; ACP, Rf = 0.42). Linearity was constructed in the range of 1.2–5 μg band−1 for CHZ, 0.5–4 μg band−1 for DIC, and 0.4–4 μg band−1 for ACP. The developed methods were applied to Declophen plus® capsules, and no interference from excipients was observed. The methods were validated as per the United States Pharmacopeia (USP) guidelines, and they were compared favorably with the reported method.