Selective and Sensitive Determination of Mercury(II) Ions in River and Sea Water by an Automatic HPLC System Combined with On-line Column Enrichment

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A selective and sensitive determination method for mercury (Hg) ions in river and sea water by reversed‐phase high performance liquid chromatography (HPLC) has been developed. A one milliliter water sample containing Hg(II) ions was put into a 4 mL sample tube. To the sample tube, 2 mL of 0.5 mol/L (M) tetrabutylammonium bromide (TBA‐Br) solution was added to form a neutral Hg compound. The Hg compound subsequently became pre‐concentrated in a mini‐column packed with 5 µm ODS. By switching the valve, the Hg compound was separated in an ODS analytical column, and detected with a photometric detector (255 nm). These processes occur automatically, except for the addition of water samples and 0.5 M TBA‐Br. The correlation coefficient of the calibration curves (metal concentration vs. peak area) obtained with 1 mL of mercury standard was more than 0.9995 over the range of 1 ng/mL (ppb) to 10 µg/mL (ppm). The detection limit of Hg ions in 1 mL solution was 0.5 ppb, which corresponded to 3 times the standard deviation (N=8) of the blank peak area. Effects of foreign ions on the method were investigated with 0.1‐ppm Hg standard and 55 metal ions. Forty two metal ions of 200 ppm did not interfere with the determination of Hg(II) ions. Tolerance limits of Pd(II) and Ag(I) were 5 and 10 ppm, respectively. Recovery tests were carried out by the presented HPLC method with spiked river and sea water samples. The recoveries with a spiked river water sample for 400‐, 40‐, and 4‐ppb Hg ion (N=5) were 100.1±0.2%, 100.1±1.3%, and 97.9±2.3%, respectively. Those with a sea water sample for 400‐, 40‐, and 4‐ppb Hg ion (N=5) were 100.9±1.0%, 99.9±1.8%, and 99.1±9.4%, respectively.