Simultaneous Determination of Mercury and Arsenic in Marine Sediments by Dual-Channel Atomic Fluorescence Spectrometry after Wet Digestion

A method was established to simultaneously determine the contents of mercury and arsenic in marine sediments by dual-channel atomic fluorescence spectrometry with wet digestion. The marine sediment sample was air-dried, ground, and sieved. 0.15 g of the sample was taken and mixed with 5 mL of nitric acid-hydrochloric acid-water mixed solution with volume ratio of 1:3:4, and the above mixture was heated in a boiling water bath for 1 h. After cooling, 5 mL of mixed solution composed of 50 g·L^-1 ascorbic acid and 50 g·L^-1 thiourea was added. The solution obtained was made up to 25 mL with water and analyzed with a dual-channel atomic fluorescence spectrometer equipped with hollow cathode lamps of mercury and arsenic. The carrier medium was 10% (volume fraction) hydrochloric acid solution, the reducing agent of 15 g·L^-1 sodium borate solution containing 2 g·L^-1 sodium hydroxide was added online, and the mixed standard solution series were prepared by automatic dilution of the instrument, with external standard method for quantification. The results showed that the mass concentrations of mercury and arsenic were linearly related to their corresponding fluorescence intensities within 5.00 μg·L^-1 and 100 μg·L^-1, with detection limits (3s/k) of 0.002, 0.03 mg·kg^-1, respectively. The spiked recovery test was made on 6 samples, and recoveries found were in the ranges of 90.3%-96.0% and 90.5%-97.8%, with RSDs (n=6) less than 5.0%.