Abstract:Geochemical samples have complex and refractory matrices. During open-vessel digestion, volatile elements such as Ge, Pb, As, Sb, Bi, Sn and Cr are liable to volatilize and lose, resulting in determination deviations of varying degrees, which seriously affect geochemical mapping and mineral resource assessment. In this work, an anti-corrosion high-pressure closed digestion vessel was adopted, and key parameters including digestion system, digestion temperature and digestion time were optimized. The optimal procedure was confirmed as follows: 0.1000 g of sample was digested with a mixture of 3 mL HF and 1 mL HNO3 in a high-pressure closed vessel at 180 ℃ for 12 h. After cooling, the polytetrafluoroethylene liner was taken out and placed on a temperature-controlled hot plate preheated to 120 ℃ to evaporate HF until the characteristic white smoke of fluorides was exhausted. Then 5 mL of 1:1 inverse aqua regia was added, and the sample was redissolved in an anti-corrosion electric oven at 180 ℃ for another 12 h, followed by dilution to 10 mL. To reduce matrix effect, ensure the concentrations of target elements fall within the linear range of standard curves, achieve the optimal balance between target elements and interfering factors, guarantee the stability of determination results and prevent nebulizer clogging, the digested solution was diluted 10-fold prior to measurement. Meanwhile, by combining kinetic energy discrimination (KED) mode with standard (STD) mode of inductively coupled plasma mass spectrometry (ICP-MS) and investigating the effects of dwell time on stability and memory effect, an analytical method for the determination of volatile elements Ge, Pb, As, Sb, Bi, Sn and Cr in geochemical samples by high-pressure closed digestion-KED-ICP-MS was established. This method effectively inhibits the volatilization loss of Ge, Pb, As, Sb, Bi, Sn and Cr, overcomes polyatomic ion interferences, and improves the sensitivity and accuracy of determination, with detection limits ranging from 0.010 to 2.03 μg/g for all elements. National first-class geochemical reference materials including soil (GBW07456), stream sediment (GBW07311) and rock (GBW07456) were determined by the proposed method, giving relative errors (RE) in the range of -5.06% to 1.67% and relative standard deviations (RSD, n=12) all less than 8.55%. Compared with traditional methods, this method reduces acid consumption by about 80%, significantly decreases laboratory waste discharge, and provides a more efficient and environmentally friendly solution for the analysis of large batches of geochemical samples. The method is simple, rapid, accurate, low in detection limit and easy to operate, which has remarkable technical progress and popularization value.