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

Abstract

For the determination of total mercury in hair, an amount (25.0 mg) of hair sample was digested with conc. HNO₃ (400 µl) 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 µl) was introduced into a graphite cuvette and then atomized according to a temperature program. The method detection limit (MDL, 3s) was 0.064 (µg g^-1); the calibration graph was linear up to 7.52 µg 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 µg g^-1; the calibration graph was linear up to 6.00 µg 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.