A new and simple procedure for the trace determination of mercury using differential pulse polarography and application to a salt lake sample

摘要

A new and simple differential pulse polarographic procedure was established for the trace determination of mercury(II). An indirect method had to be used since no polarographic peak can be observed for its direct determination. According to their standard potentials, the reaction between SO$_{3}^{2-}$ and Hg(II) was suitable. The peak height of sulfite at about -0.70 V (pH 6, 7) was sharp, high, and very reproducible, enabling the accurate determination of low concentrations of Hg(II). It was found that sulfite concentration had to be 3 times larger than mercury at pH 6, in order to have a quantitative reaction. The procedure is simple: to a known amount of sulfite in the polarographic cell (HAc, pH 6 or 7) is added an unknown Hg(II) sample. The Hg(II) concentration is calculated simply from the decrease in the sulfite peak after reaction with Hg(II). The limit of detection was 1 $imes $ 10$^{-6}$ M (S/N = 3) in this medium, which could not be obtained with most other mercury determination methods. The proposed new method exhibits high selectivity, sensitivity, reproducibility, and accuracy. It was successfully applied to synthetic samples and to a raw salt sample taken from a salt lake (closed basin) in Turkey. No considerable interference was observed from most common ions.