Food Safety and Environmental Stewardship Program

A method is presented for the determination of total mercury in environmental samples by inductively coupled argon plasma/atomic emission spectroscopy (ICP/AES) using cold-vapor generation. A 1.0 g or 10 mL test portion is digested 6–12 h in a 16 × 150 mm, 10 mL volumetric test tube at room temperature and is subsequently digested on a programmed heating block at 95°C with trace-metal grade nitric acid. The digested samples are next treated with potassium permanganate and heated between 70 and 95°C; thereafter, oxalic acid is added to reach the final endpoint. The mercury(II) is reduced by sodium borohydride in a simplified continuous manifold. A standard pneumatic nebulizer effects the gas–liquid separation of mercury. Mercury is quantitated by ICP/AES at 194.232 nm. The instrument detection limit for the method is 0.2 μg/L. Water samples are analyzed directly. The detection limit is below the current National Primary Drinking Water Standard Maximum Concentration Limit of 2 μg/L for mercury. For a 10:1 dilution of a nominal 1.0 g solid test portion, the detection limit is 2.0 μg/L. This concentration is also less than the regulatory limit of 200 μg/L for the U.S. Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure. The quantitation is linear up to 300 μg/kg. The method demonstrated statistical control for samples of biological and environmental interest.