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BACKGROUND When using inductively coupled plasma-mass spectrometry (ICP-MS) to analyze soil, the zirconium hydroxide, molybdenum oxide, and tin isotopes can cause serious interference on cadmium, which makes it difficult to accurately determine cadmium in soil samples. OBJECTIVES To develop a method for accurate determination of Cd in soil samples. METHODS ICP-MS/MS was used, and 111Cd without isobaric interference was selected as the analysis line. In MS/MS mode, the oxygen introduced into the collision reaction cell can be reacted with 111Zr16O1H+, 111Mo16O+, inducing electron transfer, dehydrogenation, oxygenation and other reactions to inhibit the overlapping interference of these polyatomic ions on 111Cd. RESULTS Oxygen flow was the key factor in this method. 0.45mL/min oxygen flow can reduce oxide interference to less than 0.005μg/L when zirconium concentration was lower than 2000μg/L and molybdenum concentration was below 1000μg/L. The method has been verified by the national reference materials. The relative error of the measured value and recognized value of the 11 national reference materials was within ±7%, and the relative standard deviation (n=12) of three soil reference materials was less than 5%. CONCLUSIONS Triple quadrupole ICP-MS oxygen reaction mode can eliminate Zr and Mo polyatomic ion interference on Cd, and this method can be used for the determination of trace Cd in soil samples.

The quality of regional geochemical survey samples is currently estimated indirectly by internal and external laboratory quality control. The method described here effectively improves the quality of geochemical samples. However, the improvement of the method is limited when the contents of the actual samples and external quality control samples have large differences. Since most elements are in accord with a normal distribution in a regional geochemical survey sample, a comparison was made between the real and standard normal distribution of the elements, which passed the normal distribution test and gave an estimate of the quality by using a comparison of the real and standard graph′s superposition using SPSS and Excel software. This method was directly applied to estimate the quality of analysis data for geochemical survey samples in Jiangxi province. The result of the normal distribution test indicated that the analysis data of the trace elements need a logarithmic conversion before the normal distribution can be studied. The quality evaluation method in this paper was not suitable for Ti, W and Cr etc in this area. The overlap ratios of 18 elements such as Co, Hg and Ga were more than 0.9. The overlap ratios of CaO and Na2O were less than 0.9. The results of the actual samples indicated that the detection limits need to be reduced in order to improve the analysis qualities of CaO and Na2O. It was a valuable attempt to directly evaluate the quality of analysis data for regional geochemical survey samples by using the method reported in this paper, which was a reference and supplement for the current methods of quality evaluation.