电感耦合等离子体串联质谱法分析凹凸棒黏土中的微量元素

凹凸棒黏土是具有层链状结构的含水富镁铝硅酸盐矿物，矿床成因不同导致凹凸棒黏土中微量元素的组成存在差异，其中Be、Cr、Ni、As、Cd、Sb、Hg、Pb会对健康和环境产生不利影响，而V、Mn、Co、Cu、Zn、Mo、Sn、Ba作为凹凸棒黏土的重要微量元素影响其性能和应用范围，因此，对凹凸棒黏土中微量元素进行精准分析可为凹凸棒黏土的高效增值深加工提供理论依据。采用电感耦合等离子体质谱法（ICP-MS）测定岩矿中微量元素具有检出限低和灵敏度高的特点，但因存在复杂质谱干扰，即使采用碰撞反应池（CRC）技术也很难完全消除。本文应用电感耦合等离子体串联质谱法（ICP-MS/MS）来消除质谱干扰，建立了准确测定凹凸棒黏土中微量元素Be、V、Cr、Mn、Co、Ni、Cu、Zn、As、Mo、Cd、Sn、Sb、Ba、Hg、Pb含量的分析方法。实验中采用由硝酸、盐酸、氢氟酸组成的混合酸对凹凸棒黏土样品进行微波消解，不仅加快了样品的消解速度，而且保持了消解溶液中分析元素的稳定。针对分析过程中所面临的质谱干扰，在MS/MS模式下，通过向CRC内加入O2和NH3/He为反应气，利用质量转移反应生成相应的氧化物离子和团簇离子消除干扰，选择质量数相近且质谱行为相似的内标元素校正基体效应，稳定了分析信号。应用本方法对国家标准参考物质玄武岩（GBW07105）中16种微量元素进行测定，分析元素的相对误差在-9.60%~8.21%之间，相对标准偏差（RSD）≤6.0%。在选定的分析条件下，各元素的检出限为0.13~51.6ng/L。本方法有效减少了质谱干扰，提高了某些特定同位素在复杂介质中的准确性和灵敏度，适合凹凸棒黏土中16种微量元素的快速测定。

Determination of Trace Elements in Attapulgite Clay by Inductively Coupled Plasma-Tandem Mass Spectrometry

BACKGROUND: Attapulgite clay is a water-rich magnesium aluminosilicate mineral with a layered chain structure. The different genesis of the deposit results in a different composition of trace elements in attapulgite clay. Elements Be, Cr, Ni, As, Cd, Sb, Hg, and Pb have adverse effects to health and environment, while V, Mn, Co, Cu, Zn, Mo, Sn and Ba can affect the performance and application of attapulgite clay. Therefore, accurate analysis of trace elements in attapulgite clay can provide a theoretical basis for the high-efficiency value-added deep processing of attapulgite clay. Determination of trace elements in rocks and minerals by inductively coupled plasma-mass spectrometry (ICP-MS) has the characteristics of low limit of detection (LOD) and high sensitivity. Complex spectral interference during the analysis is difficult to completely eliminate, even if collision reaction cell (CRC) technology is used.
OBJECTIVES: To establish an analytical method for the accurate determination of trace elements in attapulgite clay by ICP-MS/MS.
METHODS: In view of the spectral interference in the analysis process, in the MS/MS mode, O₂ and NH₃/He were added into CRC as reaction gases, and the corresponding oxide ions and cluster ions were generated by mass shift reaction to eliminate the interference. Internal standard elements with similar mass number and similar mass spectrometry behavior were selected to correct the matrix effect and stabilize the analysis signal.
RESULTS: The microwave digestion of attapulgite samples with mixed nitric acid, hydrochloric acid and hydrofluoric acid can not only accelerate the digestion speed of the sample, but also maintain the stability of the analytical elements in the digestion solution. The method was used to determine 16 trace elements in national standard reference material basalt (GBW07105). The relative errors of analytes were -9.60%-8.21%, and the relative standard deviation (RSD) was less than 6.0%. Under the selected analytical conditions, the LOD of analyte was 0.13-51.6ng/L.
CONCLUSIONS: ICP-MS/MS can effectively reduce the interference of mass spectrometry and improve the accuracy and sensitivity of some specific isotopes in complex media. The method is suitable for the rapid determination of trace elements in attapulgite clay.