氧气反应模式-电感耦合等离子体串联质谱法测定土壤中砷和硒

采用电感耦合等离子体质谱法(ICP-MS)测定土壤中的As和Se时会受到严重的氩化物、氯化物、氧化物、双电荷等多原子离子干扰,从而导致测定土壤中As和Se难度加大。采用石墨消解仪以王水消解土壤样品,在串接模式下,分别设置第一级四极杆质量过滤器(Q1)质荷比(m/z)为75和80,在碰撞/反应池中通入氧气,⁷⁵As⁺、⁸⁰Se⁺和氧气反应生成⁷⁵As¹⁶O⁺和⁸⁰Se¹⁶O⁺,而干扰离子不能与氧气反应,分别设置第二级质量过滤器(Q3)m/z为91和96,使得⁷⁵As¹⁶O⁺和⁸⁰Se¹⁶O⁺通过并进入检测器中,从而避免了质谱干扰,据此建立了石墨消解-电感耦合等离子体串联质谱法(ICP-MS/MS)测定土壤中As和Se的方法。对氧气流速进行了优化,选择氧气流速为1.0 mL/min。实验表明:As和Se的线性范围均为0.500～100 μg/L,线性相关系数分别为0.999 93和0.999 98,检出限分别为0.008 mg/kg和0.001 mg/kg,定量限分别为0.032 mg/kg和0.004 mg/kg。采用所建立的实验方法对土壤标准物质和土壤样品中的As和Se分别进行测定,结果表明,对于标准物质,As和Se的测定值均在认定值的范围内,相对标准偏差(RSD,n=6)分别在2.0%~4.4%和2.6%~7.8%之间;对于土壤样品,实验方法对As和Se的测定结果与原子荧光光谱法基本一致,相对标准偏差(n=6)分别在2.3%~4.5%和3.7%~7.9%之间。

Determination of arsenic and selenium in soil by inductively coupled plasma tandem mass spectrometry at oxygen reaction mode

The determination of As and Se in soil by inductively coupled plasma mass spectrometry (ICP-MS) can be severely interfered by polyatomic ions such as argon compounds, chlorides, oxides and double charges, leading to high difficulty in determination of As and Se in soil. The soil samples were digested by aqua regia in the graphite digester. In the MS/MS mode, the mass charge ratio (m/z) of the first quadrupole mass filter (Q1) was set to 75 and 80, respectively. Accompanied by the introduction of oxygen into the collision/reaction cell, ⁷⁵As⁺ and ⁸⁰Se⁺ were converted to ⁷⁵As¹⁶O⁺ and ⁸⁰Se¹⁶O⁺, while the interfering ions could not react with oxygen. The m/z of the second quadrupole mass filter (Q3) was set to 91 and 96, respectively, so that ⁷⁵As¹⁶O⁺ and ⁸⁰Se¹⁶O⁺ could pass through and enter the detector, avoiding the mass spectrometry interferences in the sample. Accordingly, a method for the determination of As and Se in soil by graphite digestion-inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) was established. The oxygen flow rate was optimized and 1.0 mL/min was selected. The experimental results showed that the linear range of As and Se was 0.500-100 μg/L. The linear correlation coefficients were 0.999 93 and 0.999 98, the limits of detection were 0.008 mg/kg and 0.001 mg/kg, and the limits of quantification were 0.032 mg/kg and 0.004 mg/kg, respectively. The contents of As and Se in certified reference materials and actual samples of soil were determined according to the experimental method. The results showed that the measured values of As and Se were consistent with the certified values for the certified reference materials. The relative standard deviations (RSD, n=6) were 2.0%-4.4% and 2.6%-7.8% for As and Se, respectively. For the actual samples of soil, the measured results were basically consistent with those obtained by atomic fluorescence spectrometry. The RSDs (n=6) were 2.3%-4.5% and 3.7%-7.9%, respectively.