Gravimetric determination of nickel with quinoxaline-2,3-dithiol by precipitation from homogeneous solution

The investigation of quinoxaline-2,3-dithiol as a gravimetric reagent for nickel is described. A derivative of the dithiol, S-2-(3-mercaptoquinoxalinyl)thiuronium chloride is used as a generating agent in a PFHS method because of its relative stability and solubility in aqueous ethanol. Nickel, 2.5–25.0 μg, can be precipitated at pH 2–3 as (C₈H₅N₂S₂)₂Ni. After filtration the precipitates are washed first with aqueous ethanol to remove traces of absorbed reagent and then with benzene to remove a small amount of decomposition product of the reagent, the characterization of which is described. The precipitates are stable and can be dried in air at 110–120°. Errors of less than 0.15 % are obtained in the analysis of solutions containing 25 mg of nickel. The selectivity of the reagent is discussed and some suggestions are made for masking the interference of other elements.