Spectrophotometric Determination of 2- Amino- 4- Chlorophenol as a Potential Impurity in Chlorzoxazone Bulk Drug

2-amino-4-chlorophenol (ACP) is a synthetic precursor of the skeletal muscle relaxant; chlorzoxazone. A rapid simple colorimetric method was proposed for the determination of 2amino-4-chlorophenol as a potential impurity in chlorzoxazone bulk powder via its reaction with 4-aminoantipyrine in presence of alkaline oxidizing agent (K3[Fe(CN)6] / NH3) and measuring the produced red color at 520 nm. Different experimental parameters affecting the formation of the reaction product were studied. The study included the effect of volumes of the used reagents as well as the effect of time on the formation and stability of the reaction product. The formation constant (Kf) of the reaction product was found to be 1.2 x 10 indicating a very stable reaction product. Moreover, the Gibbs free energy change of the reaction (ΔG) was found to be -2.3 x 10 K.J/mole pointing out to the spontaneous nature of the reaction. The method was successfully applied for the trace analysis of the studied compound in spiked chlorzoxazone powder. The calibration graph was linear over the range of 1-20 μg/ml with average recovery of 100.58±0.89, detection limit of 0.2 μg/ml, and quantitation limit of 0.6 μg/ml. The obtained results were statistically analyzed and were in good agreement with those obtained by the official TLC method.