Determination of Cadmium in Soil Samples by ICP-MS/MS Using Oxygen Reaction Mode

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.