Electrophoretic studies on mixed complexes

Electrophoretic studies on the chelating tendency of bioactive sulphur-containing amino acids. The metal-methylcysteine-cysteine system

Stability constants of binary Fe(III)-methylcysteine, Cr(III)-methylcysteine and mixed Fe(III)-methylcysteine-cysteine, Cr(III)-methylcysteine-cysteine complexes have been determined by paper electrophoresis at 0.1 M ionic strength and a temperature of 35 degrees C. The stability constants of Fe(III)-methylcysteine-cysteine and Cr(III)-methylcysteine-cysteine mixed complexes were found to be 6.00 +/- 0.07 and 5.05 +/- 0.15 (logarithm of stability constant values), respectively.

Spectrophotometric estimation of D-penicillamine in bulk and dosage forms using 2,6-dichloroquinone-4-chlorimide (DCQ)

A simple colorimetric method for the determination of D-penicillamine in pure form and pharmaceutical formulations is described. The method is based on coupling between D-penicillamine and 2,6-dichloroquinone-4-chlorimide (DCQ) in dimethylsulphoxide. The optimum conditions for the reaction were investigated and incorporated into the procedure. The reaction forms a yellow 1:1 complex with maximum absorbance at 431 nm (epsilon = 3,700). Regression analysis of Beer's plot showed good correlation (r = 0.9998) and the calibration graph was rectilinear over the range 4-20 microg/ml(-1) with a detection limit of 0.15 microg/ml(-1) . The average recovery for the commercial capsules was 101.66% with an RSD of 1.57%. The results obtained were sufficiently accurate, reproducible and in accordance with those given by the official method. The method is specific for the intact drug, and can be adopted in the presence of some interfering substances.