Spectrophotometric Determination of Trace Mercury(II) in Cereals with 2,4-bis(4-Phenylazophenylaminodiazo)Benzenesulfonic Acid

A simple and low cost method for the determination of mercury has been developed. The method was based upon the highly sensitive color reaction of mercury(II) ions with 2,4-bis(4-phenylazophenylaminodiazo)benzenesulfonic acid (BPPABSA). We found that in the presence of 2.0% Triton X-100, the reagent reacts with mercury to form a stable red complex in a borax buffer solution at pH 10.22. The formed complex shows an absorption maximum at 530 nm. The apparent molar absorptivity is 2.18 × 105 L/mol cm. The content of mercury in the sample was low and some foreign ions might interfere with the determination of mercury(II), so we used sulfhydryl dextran gel (SDG) to separate and enrich trace mercury(II), which lead to a satisfactory result. Under the optimal conditions, Beer's law is obeyed in the range of 0-15 µg/25 mL Hg2+, the detection limit and relative standard deviation are 0.86 ng/mL and 1.4-3.8%, respectively. The method has been applied to the determination of mercury in cereals with satisfactory results.