Selective Determination of Mercury(II) Ion in Water by Solvent Extraction Followed by Reversed‐Phase HPLC

Abstract

A selective determination method for mercury(II) ion in water by reversed‐phase high performance liquid chromatography (HPLC) has been developed. A water sample of 5 mL was put into a 10‐mL centrifuge tube with a stopper. Then, 1 mL of 2‐mol/L (M) acetate buffer solution of pH 5.5 was added into the centrifuge tube. After mixing the contents, 1 mL of 0.5 M tetrabutylammonium bromide (TBA‐Br) solution and 0.3 mL of 1‐octanol were added. A mercury ion was extracted into an organic layer by shaking the contents for 10 min. The organic layer of 8 µL was injected into a C18 column with an eluent of methanol/water/0.5 M TBA‐Br (65:31:4, v/v), and the effluent was monitored at 255 nm. The detected mercury compound was estimated as [(TBA+)2 · HgBr4 2−]0. The correlation coefficient of the calibration curves (metal concentration vs. peak area), obtained with 5 mL of mercury standard, was more than 0.999 over the range of 10 ng/mL (ppb) to 10 µg/mL (ppm). The detection limit of Hg ion in a 5‐mL solution was 0.8 ppb, which corresponded to three times the standard deviation of the blank peak area. Reproducibilities (RSD) of peak areas for 5‐, 0.5‐, and 0.05‐ppm Hg ion were 1.8%, 0.6%, and 0.6%, respectively (N = 5). Recovery tests were carried out by the presented HPLC method with spiked river water samples. The recoveries for 5‐, 0.5‐, and 0.05‐ppm Hg ion were 99.5%, 102.9%, and 99.8%, respectively. Effects of foreign ions on the method were investigated with 0.2‐ppm Hg standard and 55 metal ions. Tolerance limits of Be(II) and Sc(III) were 20 ppm, and those of Bi(III) and Pd(II) were 40 ppm. The other metal ions of 100 ppm, or more, did not interfere with the determination of mercury(II) ion.