Determination of 7 Heavy Metal Elements in Soil by Inductively Coupled Plasma Mass Spectrometry with Automatic Graphite Digestion

The soil sample (0.200 0 g) was taken and placed in a 50 mL-polytetrafluoroethylene digestion tube, and wetted with a small amount of water. 4.5 mL of hydrochloric acid, 1.5 mL of nitric acid, 3 mL of hydrofluoric acid and 1 mL of perchloric acid were used as the digestion system, and the mixture was digested by a automatic graphite furnace digester according to the program. The mixture was taken and cooled for 10 min, and made its volume up to 25 mL with 5% (volume fraction) nitric acid solution. An aliquot (2.5 mL) of the solution was taken, made its volume up to 25 mL with 2% (volume fraction) nitric acid solution, and mixed well online with 10 μg · L⁻¹ of ¹⁸⁵Re and ¹⁰³Rh internal standard solution, in which 7 heavy metal elements, including arsenic, copper, lead, zinc, chromium, cadmium, nickel were determined by inductively coupled plasma mass spectrometry. As shown by the results, linear relationships between the ratios of the corresponding signal intensity to the internal standard signal intensity and mass concentrations of 7 heavy metal elements were kept in definite ranges, with detection limits (3s) in the range of 0.008-0.07 mg · kg⁻¹. Tests for accuracy and precision on the soil standard samples GSS-29, GSS-31 and GSS-34 were carried out, and the absolute values of the relative errors of the determined values were less than 7.0%, and RSDs (n=6) of the determined values of the 6 elements except cadmium were less 5.0%. Compared with the traditional electric hot plate digestion method, the accuracy and precision of this method were better.