Determination of nickel in biological samples spectrophotometrically involving complexation reaction with some thiazolylazo compounds

Three new heterocyclic azo compounds, 5(2-benzothiazolylazo)2,2 biphenyldio l (I), 5-(2-benzothiazolylazo)-8-hydroxyquinolene (II) and 4-(2-benzothiazo -lylazo)3-hydroxy-2-naphthoic acid (III) were synthesized. The formation co nstant of the reagents in 30% (v/v) ethanol and reactions with various meta l ions were studied. These reagents (I-III) reacts with nickel ion to form (2 : 1) colored complex with an absorption band at 604, 635 and 643 nm. The apparent stability constants and the optimum conditions for complete color development were investigated. Beer's law is obeyed over the concentration ranges of 0.05-3.50, 0.05-4.00 and 0.05-3.10 mug ml(-1). For more accurate analyses, Ringbom optimum concentration ranges were found to be 0.20-3.25, 0.20-3.80 and 0.20-2.90 mug ml(-1) using reagents I, II and III, respectiv ely. The apparent molar absorptivity and Sandell sensitivity were also calc ulated. The interference of various foreign ions on the determination of ni ckel was investigated. The proposed method has been successfully applied to the determination of nickel substrates in various biological samples.