Determination of 26 Trace Elements in Diatomite by ICP-MS with Digestion in Pressure Vessel

Sample dissolution in ICP-MS determination of 26 trace elements in diatomite was modified by digestion in pressure vessel and complete dissolution of sample including the high field strength elements of niobium, tantalum, zirconium, hafnium was attained. 0.10 g of the sample was placed into the PTFE inner vessel, and after moistening with a small amount of water, 2 mL of nitric acid and 5 mL of hydrofluoric acid were added. The inner vessel was then placed into the outer digestion vessel, and after sealing hermetically, it was digested for 24 h in a drying oven controlled at 185℃. After cooling, the PTFE inner vessel was taken out, after addition of 1 mL of nitric acid the solution in the vessel was evaporated to near-dryness. The addition of nitric acid and evaporation to near-dryness were repeated for 3 times to expel hydrofluoric acid completely. Then 5 mL of mixed acid of HCl+HNO₃+H₂O with a volume ratio of 3:1:4 were added to the residue, and the inner vessel with the solution mixture was placed back into the outer vessel. The digestion vessel was hermetically sealed and digested again in the oven at 185℃ for 8 h to attain complete dissolution. At the end of digestion, the digestion vessel was cooled to room temperature, the inner vessel containing the sample solution was taken out and the volume of the solution was made up to 25 mL with water. An aliquot of 5.0 mL from the solution was taken and made up its volume to 25 mL with water. This solution was used for ICP-MS analysis under the optimum working condition of the interument. ¹⁰³Rh was added to either the sample solution and the mixed standard solutions for preparation of standard curves to have a concentration of 10 μg·L^-1 as internal standard. Linear relationships between values of ratios of response determined to the response of the internal standard and the mass concentrations of the 26 elements in definite ranges were found. Detection limits (3s) found for the 26 elements were in the range of 0.003-0.2 μg·g^-1. A CRM (GBW 07107) was analyzed by the present method, giving results in consistency with the certified values. Values of RSDs (n=8) found for the 26 elements were in the range from 1.3%-5.6%. Three diatomite samples taken separately from 3 main mining areas in our country were analyzed by this method, and the chondrite-normalization patterns of rare earth elements was prepared. It was found that contents of light rare earth elements were higher than the contents of heavy rare earth elements for all the 3 samples, and that the 3 pattern curves showed very smooth trend and same well defined negative anomaly of europium. The results were in consistency with those reported in literatures.