A new thiazolylazo reagent, 2-[2-(5-methylbenzothiazolyl)azo] -5-dimethylaminobenzoic acid (5-Me-BTAMB) was synthesized. Its chromogenic reaction with microamounts of nickel was studied in detail, and the stability constants of the complexes of Ni2+, Co2+, Fe2+, Cu2+ and Pd2+ were determined. 5-Me-BTAMB reacts with nickel(II) in the presence of sodium dodecyl sulfate to form a stable blue–violet 2:1 complex with an absorption maximum at 640 nm. The molar absorptivity of the complex is 1.32 × 105 l mol–1 cm–1. Beer’s law is obeyed in the range 0–10 µg of nickel(II) per 25 ml. The proposed method was applied to the direct determination of microamounts of nickel in aluminium alloys with satisfactory results.
