Inhibitory kinetic spectrophotometric method for the quantitative estimation of d-penicillamine at micro levels

• An inexpensive kinetic method is developed for determining d-Penicillamine in drugs.
• d-Penicillamine is determined in environmental samples in micro molar range.
• The method to determine d-PA in tablets is based on ligand substitution reaction.
• The method is quite simple, reliable and inexpensive for d-PA determination.
• This method may be used for the monitoring of d-PA in drug formulations.

Biologically active thiol, d-penicillamine (d-PA), based on the hard soft acid base (HSAB) principle, binds strongly with Hg(II) ions leading to the inhibition of the rate of Hg(II) catalyzed substitution of cyanide in hexacyanoruthenate(II) i.e. [Ru(CN)6]4 − by nitroso-R-salt (NRS). This formed the basis for the development of a novel kinetic spectrophotometric method for the quantitative determination of d-PA at micro levels. The reaction was followed spectrophotometrically at 525 nm (λmax of [Ru(CN)5NRS]3 − complex) under optimized reaction conditions at 8.75 × 10− 5 M [Ru(CN)64 −], 3.50 × 10− 4 M [NRS], pH 7.00 ± 0.02, ionic strength (μ) 0.1 M (KCl) and temperature 45.0 ± 0.1 °C. The modified mechanistic scheme is proposed to understand the inhibition caused by d-PA on Hg(II) catalyzed substitution of cyanide by NRS in [Ru(CN)6]4 −. The detection limit of the proposed method was found to be 2.5 × 10− 7 M. The method has successfully been applied for the determination of d-PA in real samples with quantitative results.