Analytical Sciences

Determination of Total Mercury and Methylmercury in Human Hair by Graphite-Furnace Atomic Absorption Spectrophotometry Using 2,3-Dimercaptopropane-1-sulfonate as a Complexing Agent

Wen-Yi CHEN, Yu-Chun WANG, and Mao-Sung KUO 

Department of Environmental Science, Tunghai University, Taichung 407, Taiwan, Republic of China

For the determination of total mercury in hair, an amount (25.0 mg) of hair sample was digested with conc. HNO₃ (400 ul) at 90°C for 10 min in a 7-ml teflon microreaction vessel. After digestion, the pH of the acidic hair mixture was adjusted to 5.0 - 6.0 by NaOH and was then passed through a clean-up Sep-Pak C₁₈ cartridge. To the eluate, 2,3-dimercaptopropane-1-sulfonate (DMPS) and sodium acetate buffer (pH = 6.0) were added to form a mercury-DMPS complex. This complex was preconcentrated on two Sep-Pak C₁₈ cartridges in series, and each cartridge was eluted with methanol and adjusted to 2.00 ml. A portion (50 ul) was introduced into a graphite cuvette and then atomized according to a temperature program. The method detection limit (MDL, 3sigma) was 0.064 (ug g^-1); the calibration graph was linear up to 7.52 ug g^-1. Good accuracies were obtained when testing two human hair certified reference materials (GBW 09101 and BCR-397). Six real samples were analyzed, and the recoveries were 95.8 - 98.2% with a relative standard deviation (RSD, n = 3) < 2.1%. For the determination of methylmercury (CH₃Hg⁺), 25.0 mg of hair sample was extracted with 2.0 mol dm^-3 HCl (1.0 ml) by ultrasonicating for 1 h. The supernatant solution was used for CH₃Hg⁺ analysis and the hair residue was used for the analysis of inorganic mercury (Hg²⁺). The MDL of CH₃Hg⁺ was 0.068 ug g^-1; the calibration graph was linear up to 6.00 ug g^-1. Six real samples were analyzed, and the recoveries were 96.0 - 99.2% with RSD (n = 3) < 2.3%. The sum of the concentrations of CH₃Hg⁺ and Hg²⁺ was very close to that of the total mercury measured with a relative error within 3.6%. The proposed method can be accurately applied to the measurement of CH₃Hg⁺, Hg²⁺, and total mercury in hair samples.

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