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 pu re form and pharmaceutical formulations is described. The method is based o n coupling between D-penicillamine and 2,6-dichloroquinone-4-chlorimide (DC Q) in dimethylsulphoxide. The optimum conditions for the reaction were inve stigated and incorporated into the procedure. The reaction forms a yellow 1 :1 complex with maximum absorbance at 431 nm (epsilon = 3700). Regression a nalysis of Beer's plot showed good correlation (r = 0.9998) and the calibra tion graph was rectilinear over the range 4-20 mu g ml(-1) with a detection limit of 0.15 mu g ml(-1). The average recovery for the commercial capsule s 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 m ethod. The method is specific for the intact drug, and can be adopted in th e presence of some interfering substances. (C) 1999 Elsevier Science B.V. A ll rights reserved.