Determination of 7 Heavy Metals in Marine Sediments Based on Graphite Digestion Method

In view of the problems of low work efficiency, complex operation, cross-contamination and high personnel risk in the digestion methods of heavy metals in marine sediments commonly used at present, the fully automatic graphite digestion method was proposed for marine sediments, with atomic fluorescence spectrometry for the determination of mercury and arsenic, and inductively coupled plasma mass spectrometry for the determination of copper, lead, zinc, cadmium and chromium by comparing and referring to different digestion methods of heavy metal in marine sediments in current norms, standards and literatures. The sample (0.2 g) was digested with 6 mL of hydrochloric acid, 2 mL of nitric acid and 8 mL of water at 100 ℃ for 1.5 h. After digestion, the solution was cooled to room temperature, and its volume was made up to 50 mL with water, in which mercury and arsenic were determined according to the operating conditions of the atomic fluorescence spectrophotometer. Using 5 mL of hydrochloric acid and 5 mL of nitric acid as the digestion acids, 0.2 g of sample was digested firstly at 120 ℃ for 1 h. Then 2 mL of nitric acid, 5 mL of hydrofluoric acid and 2 mL of perchloric acid were added, and the sample was digested sequentially at 180 ℃ for 4 h. After digestion, the solution was cooled to room temperature, and its volume was made up to 50 mL with water, in which copper, lead, zinc, cadmium and chromium were determined according to the operating conditions of the inductively coupled plasma mass spectrometer. As shown by the results, the linear ranges of standard curves for mercury and arsenic were within 1.00 μg·L^-1 and 10.0 μg·L^-1, and the linear ranges of standard curves for copper, lead, zinc, cadmium and chromium were within 100 μg·L^-1, with detection limits (3s) of mercury, arsenic, copper, lead, zinc, cadmium and chromium in the range of 0.006-0.522 mg·kg^-1. The certified marine sediment reference materials were used for validation, and it was shown that the determined values of 7 heavy metals were all in the uncertainty range of the certified values, with RSDs (n=6) in the range of 1.4%-7.4%. Test for recovery was made on the actual samples, giving results in the range of 92.5%-111%.