A catalytic determination method for mercury has been developed by combining two catalytic reactions: mercury-catalyzed dissociation of iron from Fe(CN)64− and iron-catalyzed oxidative coupling of 3-metyl-2-benzothiazoline hydrazone with N,N-dimetylaniline in the presence of H2O2. Under an optimized reaction condition, the first reaction was carried out for a reaction time of 10 min at a reaction temperature of 60°C and the second reaction was done for 5 min at 25°C. The absorbance of an indamine dye produced by the second reaction was measured at 590 nm. The absorbance was proportional to the concentration of mercury. The concentration of toxic CN− generated from the first reaction was reduced to that much less than the effluent standard in Japan. Mercury was separated from interfering foreign ions by the reducing evaporation at 40°C for 10 min using a Conway microdiffusion unit. Mercury ions in sample were reduced by tin(II), and mercury vapor generated was absorbed into an acidic permanganate solution. The interference of chloride ion, evaporating with mercury, was inhibited by adding thiourea into the sample. In the analysis of a 1-mL sample, the calibration curve of mercury was linear up to 200 ng mL−1, and the detection limit of mercury was 5 ng mL−1. The proposed method was applied to river water and industrial waste samples. The recoveries of mercury (50 or 150 ng) added were satisfactory within an error of 5 %.
