Selective Spectrophotometric Determination of Metformin Hydrochloride in Pharmaceuticals and Urine Using Two Nitrophenols as Chromogenic Agents

Metformin hydrochloride (MFH) is an oral anti-diabetic drug of biguanide class. Two selective spectrophotometric methods were presented for the determination of MFH in pharmaceuticals. The methods were based on the measurement of yellow-coloured charge-transfer complexes formed between MFH and two poly-nitrophenols, namely, 2,4-dinitrophenol (DNP method, at 405 nm) and picric acid (PA method; at 410 nm) in dichloromethane medium. The variables which affect the complex formation were studied and optimized. Beer’s law was obeyed over the concentration ranges: 2.4-48.0 and 3.2-64.0 µg ml-1 with molar absorptivity values of 3.24 × 103 and 2.30 × 103 l mol-1 cm-1, with DNP method and PA method, respectively. The limits of detection (LOD) and quantification (LOQ) were calculated to be 0.13 and 0.40 µg ml-1 for DNP method and 0.19 and 0.59 µg ml-1 for PA method. Methods were validated for accuracy, precision, robustness, ruggedness and selectivity. The proposed methods were applied to the determination of MFH in tablets. The accuracy and precision of the methods were found excellent. Accuracy of the methods was ascertained by recovery test via standard-addition procedure. The methods were applied to spiked human urine sample without detectable interference from endogenous substances.