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Determination of pharmaceutical active thiolic compounds, penicillamine, cysteine, tiopronine and glutathione by flow injection analysis with spectrophotometric detection

The flow-injection (FI) spectrophotometric procedure for the determination of pharmaceutical active thiolic compounds, penicillamine, cysteine, tiopronine and glutathione has been developed and validated. The developed method is based on the reduction of Cu(II)-neocuproine reagent to yellow Cu(I)-neocuproine by the sulfhydryl group of thiolic compounds in aqueous solutions under mild acid condition (pH = 3) which absorbance is measured at 458 nm. Cu(II)-neocuproine reagent is a selective oxidant because only the reducing substances with standard (formal) potentials lower than 0.6 V would have the thermodynamic properties to interfere in the proposed method. In addition, kinetic properties of Cu(II)-neocuproine provide excellent sensitivity probably because Cu(I)-neocuproine is a fast forming product of a single electron reduction with thiol compounds. Therefore, proposed method is sensitive enough to enable determination of near nanomole amounts of thiol compounds without expensive instruments with the analytical frequency of 120 h−1 for penicillamine and glutathione and 180 h−1 for cysteine and tiopronine. Main chemical and instrumental variables were examined thoroughly. The proposed method was validated in terms of linearity range, limit of detection and limit of quantitation, selectivity, precision and accuracy. A linear calibration curves for cysteine, penicillamine and tiopronine are established in a concentration range of 6×10−7 to 4×10−5 mol L−1 with detection limit of 2×10−7 mol L-1 and working dynamic range of glutathione is from 2×10−6 to 3×10−5 mol L−1. The proposed method was applied to determine these thiols in their dosage forms. The results were compared favorably with those obtained by their pharmacopeial methods.

penicillamine ; cysteine ; tiopronine ; glutathione by flow injection analysis ; spectrophotometric detection

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