氧气反应模式-电感耦合等离子体串联质谱法测定土壤中的镉

应用电感耦合等离子体质谱法(ICP-MS)分析土壤中的镉元素时，锆的氢氧化物、钼的氧化物、锡的同位素会对镉造成严重的干扰，导致准确测定土壤中镉的难度较大。本文采用电感耦合等离子体串接质谱法(ICP-MS/MS)，选取无同质异位素干扰的111Cd为分析谱线，在MS/MS模式下碰撞反应池中通入的氧气可以与94Zr16O1H+、95Mo16O+进行电子转移、去氢、加氧等反应，抑制这些多原子离子对111Cd的重叠干扰。结果表明：氧气流量越大，去除多原子离子的效果越好，当氧气流量在0.45mL/min时，溶液中2000μg/L以下的锆、1000μg/L以下的钼在111Cd处形成的多原子重叠干扰小于0.005μg/L。实验在石墨消解仪中采用氢氟酸-硝酸-高氯酸消解样品，盐酸复溶，溶液定容稀释至1000倍测定，方法检出限(3δ)达到0.003μg/g；本方法经过国家土壤一级标准物质验证，11个国家土壤一级标准物质的测量值和认定值的相对误差在±7%以内，3个国家土壤一级标准物质的精密度(RSD，n=12)小于5%。本方法可以作为土壤样品中痕量镉元素的分析方法。

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 111 Zr¹⁶O¹H⁺,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.