电感耦合等离子体质谱法测定高锡地质样品中的痕量镉

Determination of Low-content Cadmium in Sn-rich Geological Samples by Inductively Coupled Plasma-Mass Spectrometry

应用电感耦合等离子体质谱法(ICP-MS)测定地质样品中的痕量镉,存在多种质谱干扰,通常采用在线或离线方程进行校正,当样品中含锡较高时,采用传统固定系数校正方程,易导致测定结果有明显偏离,甚至结果出现负数。本文针对含高锡的地质样品,应用ICP-MS测定其中的镉,采用氢氟酸-高氯酸-硝酸敞开酸溶消解、硝酸浸提体系处理样品,通过测定111Cd、113Cd、114Cd同位素,研究了干扰元素Sn、In、Zr、Mo对镉测定的影响。结果表明镉与干扰源浓度变化呈非简单的正相关性。①同质异位素Sn或In产生的干扰增值Δ(114Cd/^114Sn或113Cd/^113In)随干扰源浓度增大逐渐变大,114Sn对^114Cd的干扰系数在0.0272~0.0222,113In对^113Cd的干扰系数在0.0670~0.0412;②Zr和Mo在测定条件下形成氧化物和多原子复合离子物质对Cd均产生不同程度的质谱干扰。通过测定与样品中干扰源浓度相近的单一标准溶液产生的Cd干扰值,经在线修正干扰系数(γ),建立了精确的校正方程。该方法经标准物质验证,准确度高,相对标准偏差在6.57%~9.94%(n=7),方法检出限为0.03mg/kg,达到了地质分析检测要求,为高锡地质样品中的痕量镉分析提供了依据。

BACKGROUND: There are many kinds of mass spectral interferences when inductively coupled plasma-mass spectrometry(ICP-MS) is used to determine trace amounts of cadmium in geological samples. Usually, on-line or off-line equations are used for correction. When the sample has high tin content, traditional fixed coefficient correction equations can easily lead to significant deviations in the results, and even negative results.OBJECTIVES: To develop a method for the determination of low-level Cd in high-Sn samples.METHODS: The system of hydrofluoric acid-perchloric acid-nitric acid digestion and nitric acid compound solvent were applied to analyze the cadmium isotopes, 111Cd, 113Cd and 114Cd for high-tin samples. The influence of interference elements, Sn, In, Zr and Mo on the determination of cadmium was studied.RESULTS: Results showed that there was a non-simple positive correlation between cadmium concentration and the concentration variations of interference sources. The interference increment value increased gradually with the concentration of interference elements. The interference coefficient of 114Sn on 114Cd ranges from 0.0272 to 0.0222, and that of 113In on 113Cd was 0.0670 to 0.0412. Cadmium suffers from different degrees of Zr and Mo based oxide/hydroxide mass spectrometry interferences. By measuring the cadmium interference value produced by a single standard solution close to the concentration of the interference source in the sample, the interference coefficient(γ) was corrected on-line to establish an accurate correction equation. The method has been verified by a series of certified standard substances with high accuracy and precision of 6.57%-9.94%(n=7). The method had the Cd detection limit of 0.03 mg/kg, which met the requirements of geological sample analysis.CONCLUSIONS: The method provides a feasible basis for the determination of low-content cadmium in high-Sn geological samples.