Spectrophotometric determination of clozapine in pharmaceuticals

New spectrophotometric methods for the assay of clozapine (CZP) in pure and dosage forms are described. Method A is based on the oxidative coupling reaction of CZP with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in the presence of eerie ammonium sulphate to form a coloured species (lambda(max) 570 nm). Method B is also based on the oxidative coupling reaction of CZP with P-N,N-dimethylphenylenediamine dihydrochloride (DMPD) in the presence of sodium hypochlorite to form a coloured species (lambda(max) 690 nm). Method C is based on the formation of coloured charge-transfer complex between CZP and chloranilic acid (lambda(max) 540 nm). Regression analysis of Beer-Lambert plots showed good correlation in the concentration ranges 2-25, 10-120 and 15-300 mu g/ml for methods A, B and C, respectively. The validity of the proposed methods was tested by analysing pharmaceutical dosage forms containing CZP and the relative standard deviation values were within 1.0%.