Colorimetric microdetermination of Mercury(II) with some quinoxaline azo compounds in presence of an anionic surfactant

A new simple, rapid, sensitive, and selective method is proposed for the mi crodetermination of mercury. Mercury(II) forms insoluble complexes with 2,3 -dichloro-6- (2-hydroxy-3,5-dinitrophenylazo)-quinoxaline (1), 2,3-dichloro -6-(5-amino-3-carboxy-2-hydroxy-phenylazo)-quinoxaline (2), 2,3-dichloro-6- (2,7-dihydroxynaphth-1-ylazo)-quinoxaline (3), and 2,3-dichloro-6-(3-carbox y-2-hydroxy-naphth-1-ylazo)-quinoxaline (4) in aqueous acidic medium; the c omplexes can be made soluble by the action of an anionic surfactant. The so lution of the pink coloured compounds is stable for at least 24 h. Beer's l aw is obeyed over the concentration range from 0.1 to 2.8 mug . cm(-3) of m ercury. For a more accurate analysis, Ringbom optimum concentration ranges were found to be 0.25-2.5 mug . cm(-3). The molar absorpitivity, Sandell se nsitivity, and relative standard deviations were also calculated. A slight interference from Pd2+ and Cd2+ is exhibited by the first three ligands, wh ereas the last one is only negligibly affected by these metal ions. Strong interference from Ag(I) is evident for all ligands, whereas alkali, alkalin e earth, and other transition metals tested posed negligible interference. 15 mug . cm(-3) of Cd2+ and Pd2+ or 10 mug . cm(-3) of Ag+ can be tolerated if 1.0 mg of potassium bromide and 2.0 mg of citrate as masking agents are added for the determination of 1.5 mug . cm(-3) of mercury(II). The method was applied to the determination of methyl- and ethylmercury chloride and the analysis of environmental water samples.