Measurement of Total Mercury in Sedments by Graphite-Furnace Atomic Absorption Spectrophotometry Using 2, 3-Dimercaptopropane-1-sulfonate as a Complexing Agent

An amount (50 mg) of dried sediment sample was digested with a mixture of aqua regia (700 μL) and hydrofluoric acid (50 μL) at 80℃ for 10 min in a 7-mL teflon microvessel. After digestion, the pH of the acidic sediment mixture was adjusted to 6.5-7.0 by NaOH. The sediment residue was removed by passing the mixture through a 0.45 μm filter membrane. To the filtrate, sodium acetate buffer (pH=6.0) and 2, 3-dimercaptopropane-1-sulfonate (DMPS) were added to form a mercury-DMPS complex. The complex was preconcentrated on two home-made C18 cartridges in series, and each cartridge was eluted with methanol and adjusted to 0.50 mL. A portion (50 μL) was introduced into a graphite tube and then measured by GFAAS. The peak heights in absorbance were used for a quantitative analysis. The method detection limit (MDL, 3σ) was 6.8 ng/g; the calibration graph was linear up to 308 ng/g. Good accuracies were obtained when testing four sediment certified reference materials (GBW 07305, CRM 016-050, GBW 07311, and BCR CRM-580). Four real river sediment samples collected from central Taiwan were analyzed, and the recoveries were in the range of 97.0-102.0% with a RSD (n=3) ＜4.7%. The proposed method can be applied to the measurement of total mercury in sediment samples.