Determination of cadmium, copper, mercury, lead and zinc mass fractions in marine sediment by isotope dilution inductively coupled plasma mass spectrometry applied as a reference method
Determination of cadmium, copper, mercury, lead and zinc mass fractions in marine sediment by isotope dilution inductively coupled plasma mass spectrometry applied as a reference method
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DOI：
10.1016/j.microc.2016.05.002
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发表时间：
2016-09
影响因子：
4.8
通讯作者：
I. Wysocka;E. Vassileva
中科院分区：
文献类型：
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作者：
I. Wysocka;E. Vassileva
采用同位素稀释电感耦合等离子体质谱法（IDICP-MS）测定海洋沉积物候选标准物质IAEA-458中Cd、Cu、Hg、Pb和Zn 5种微量元素的总质量分数。由于样品的基质相当复杂且存在预期的光谱干扰，因此对所用方法的验证（尤其是其测量步骤）进行了特别注意。通过四极电感耦合等离子体质谱仪（ICP-QMS）或扇形场电感耦合等离子体质谱仪（ICP-SFMS）进行参考同位素测量。为了考察所用技术在参考测量数据质量方面的等效程度，进行了比较研究，为了减少分析步骤的数量，采用了多次加标方法。在微波消化混合物样品后进行测量，确保完全同位素平衡。在低分辨率模式下，通过ICP-QMS或ICP-SFMS进行基质分离后测定Cd。此外，镉同位素比值测定的ICP-QMS操作碰撞反应模式，没有分离的矩阵。采用中等分辨率的ICP-SFMS和ICP-QMS方法测定Zn和Cu。铅同位素比值的测定在标准模式下操作的ICP-QMS。由于样品中汞含量较低，因此汞同位素比值的测量仅采用ICP-SFMS进行，整个ID ICP-MS测量过程用数学方程描述，并对合成不确定度进行了估计。系统地研究了影响最终结果的所有因素及其不确定度。这包括程序空白、沉积物材料中的水分含量和影响混合比测量的参数（仪器背景，光谱干扰，死时间和质量区分效应以及测量的同位素比率的可重复性）通过不同测量技术确定的质量分数值之间的良好一致性证明，所有潜在的问题都来自复杂的沉积物基质和光谱干扰。都解决了所获得的结果的一致性证实，ICP-QMS可以选择的方法，即使是参考测量，当样品中的元素含量是足够高的，在分析过程中的所有步骤都得到了很好的描述和理解。分析过程的建模导致测量程序的充分验证，建立测量结果的可追溯性和估计现实的最终扩展不确定度。与所得质量分数相关的综合不确定度相当小（Cd、Cu、Zn和Pb为2%，Hg为4.9%，k= 2），并与参考测量的主要假设一致。开发的程序已成功地应用于IAEA的表征-458候选参考物质，以及用于计算在广泛的世界原子能机构-458实验室间比较研究的框架中的赋值。
Isotope Dilution Inductively Coupled Plasma Mass Spectrometry (ID ICP-MS) has been applied for the determination of the total mass fractions of five trace elements (Cd, Cu, Hg, Pb and Zn) in marine sediment candidate reference material IAEA-458. Because of the rather complex matrix of the sample and the expected spectral interferences, special care was taken for the validation of the applied method, particularly for its measurement step. Reference isotopic measurements were carried out by quadrupole inductively coupled plasma mass spectrometer (ICP-QMS) or by sector field inductively coupled plasma mass spectrometer (ICP-SFMS). Comparative studies were performed with the aim to examine the degree of equivalence between employed techniques in terms of the high requirements for the quality of reference measurement data.In order to reduce the number of analytical steps multiple spiking approach was applied. The measurements were performed after a microwave digestion of the blend samples assuring complete isotopic equilibration. Cd was determined after matrix separation by ICP-QMS or ICP-SFMS at low resolution mode. Additionally Cd isotopic ratios were measured by ICP-QMS operated in collision reaction mode, without separation of the matrix. ICP-SFMS at medium resolution and ICP-QMS methods were used for Zn and Cu determinations. Pb isotopic ratios were measured by ICP-QMS operated in standard mode. Because of the low Hg content in the sample Hg isotopic ratios measurements were carried out only by ICP-SFMS.The entire ID ICP-MS measurement process was described by mathematical equations and the combined uncertainty was estimated. All factors influencing the final results and their uncertainties were systematically investigated. This included procedural blank, moisture content in the sediment material and parameters affecting the blend ratio measurements (instrumental background, spectral interferences, dead time and mass discrimination effects as well as the repeatability of measured isotopic ratios).The excellent agreement between mass fraction values determined by different measurement techniques proved that all potential problems coming from the complex sediment matrix and the spectral interferences were solved. The consistency of the obtained results confirmed that ICP-QMS can be the method of choice even for the reference measurements, when the element content in a sample is sufficiently high and all steps in the analytical procedure are well described and understood.The modeling of the analytical process resulted in adequate validation of measurement procedure, establishing traceability of the measurement results and estimating the realistic final expanded uncertainty. The combined uncertainties associated to the obtained mass fractions were considerably small (2% for Cd, Cu, Zn and Pb and to 4.9% in the case of Hg,k= 2) and in line with the primary assumption to the reference measurements.The developed procedure has been successfully applied for the characterisation of the IAEA-458 candidate reference material as well as used in the calculation of the assigned values in the frame of wide world IAEA-458 inter-laboratory comparisons study.