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Determination of penicillamine in pharmaceutical formulations using kinetic method with spectrophotometric detector

Novel simple kinetic spectrophotometric method for the determination of penicillamine (PEN) has been developed and validated. Penicillamine, an organosulfur compound, is an amino acid that contains an additional SH group. PEN has strong chelating effect, therefore is used to treat Wilson’s disease by forming stable complex with copper and also for lead, mercury and arsenic poisoning. The method is based on a fast one-step redox reaction wherein PEN reduces the Cu(II)-bathocuproine complex to the yellow-orange Cu(I)-bathocuproine complex. The generated reduced, stable coloured, complex exhibits absorption maximum at 483 nm. The parameters of the chemical reaction have been optimized and the effect of interfering substances was also investigated. Using kinetic spectrophotometric measurements, the initial rate and fixed time (at 1 min) methods were utilized for constructing the calibration graphs. Initial reaction rates were determined from the slopes of the absorbance-time curves. The logarithms of the reaction rates were plotted as a function of logarithms of PEN concentrations. The graph was linear in concentration range from 6.0 x 10-7 to 4.0 x 10-5 mol L-1 with the regression equation y = 1.0448 x + 3.2997 (R2 = 0.9986). The slope of the calibration curve (1.0448) confirmed the first order reaction. The graph of the fixed time method was linear in concentration range from 2.0 x 10-7 to 4.0 x 10-5 mol L-1 with the regression equation y = 12987 x - 0.0002 (R2 = 1.0000), and the limit of detection 6.0 x 10-8 mol L-1. No interferences were observed from the excipients that are commonly present in the pharmaceutical formulations. The proposed method is accurate (recovery in the range from 99.4% to 101.5%) and is successfully applied for the determination of PEN in its commercial pharmaceutical formulation, which is compared to the official potetiometric method.

penicillamine ; kinetic ; spectrophotometric

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