Method for the Determination of Trace Elements in the Carbonate Fraction of Marine Sediments
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摘要: 海相沉积物中自生沉积碳酸盐相的微量元素携带极为丰富的原始地质信息，然而海相沉积物中碳酸盐相的测定还没有建立统一的标准方法。本文以修正的Tessier七步提取流程为基础，以电感耦合等离子体质谱法(ICP-MS)为检测手段，针对海相沉积物碳酸盐相组分中V、Cr、Co、Ni、Sr五种微量元素建立了分级提取方法。实验以海相沉积物样品和标准物质作为参考样品，对比了NaAc和EDTA提取碳酸盐相的效果。结果表明，NaAc不能完全提取出沉积物碳酸盐相中的微量元素；EDTA可以较好地提取自生海相沉积物碳酸盐相中的微量元素，但是由于其络合能力太强还会提取有机物结合态的金属元素。本研究确定的分级提取方法是：首先用中性盐NaCl去除离子交换态，然后用提取专一性较强的焦磷酸钠(pH=10)去除有机态，再用EDTA提取仅自生海相沉积物的碳酸盐相。方法精密度(RSD)均 < 5%，各元素的检出限在0.5~4.3 ng/g之间，回收率在88.0%~101.6%之间，方法的选择性和稳定性能够满足地球化学样品形态分析的要求。Abstract: Trace elements in the carbonate of marine sediments carry abundant original geological information. However, there is no uniform standard method for the determination of carbonate in marine sediments. In this paper, an extraction method is described for five kinds of trace elements (V, Cr, Co, Ni and Sr) of carbonate phase in the marine sediments by using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), which is based on the modified seven steps extraction processes by Tessier. Two extraction agents (EDTA and NaAc) were used to extract carbonate fraction for marine sediment samples and standard materials. The results indicate that the NaAc cannot be used to fully extract the trace elements from the carbonate phase in sediments. The EDTA can better extract the carbonate phase of marine sediments, but organic complex metals were also extracted based on the strong complexation ability for metallic elements. In this experiment, we initially removed the ion exchange state by using NaCl and excluding the organic material by pyrophosphate (pH=10) which was an extractant with strong selectivity. Next, the terragenous carbonate of marine sediments was extracted by EDTA. The precision of the method was less than < 5%, the detection limit of each element was in the range of 0.5-4.3 ng/g, and the recoveries were between 88.0%-101.6%. Selectivity and stability of the method meet the requirements of geochemical sample morphological analysis.
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表 1 ICP-MS工作参数
Table 1 Instrument parameters of ICP-MS
工作参数 设定条件 高频发射功率 1100 W 等离子体气(Ar)流量 15.0 L/min 辅助气(Ar)流量 1.2 L/min 雾化气流量 0.98 L/min 透镜电压 6.0 V 
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表 2 NaAc和EATA提取方法分析结果对比
Table 2 Comparison of analytical results with NaAc and EDTA extraction methods
提取方法 样品编号 w/(μg·g-1) V Cr Co Ni Sr NaAc提取(方法1) 样品1 0 0.06 0.17 0.28 0.42 样品2 0 0.06 0.17 0.23 0.39 GBW 07436 0 0.014 0.013 0.062 0.09 EDTA提取(方法2) 样品1 1.39 2.95 3.27 2.97 5.11 样品2 1.23 3.15 3.2 2.62 5.35 GBW 07436 0.85 0.05 1.7 1.1 1.85
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表 3 有机态去除后EDTA提取方法测定结果
Table 3 Analytical results of elements with EDTA extraction method after eliminating the organic state
提取方法 样品编号 w/(μg·g-1) V Cr Co Ni Sr Na4P2O7去除有机态，EDTA提取 样品1 0.57 1.58 2.80 2.58 3.19 样品2 0.52 2.03 2.40 2.28 3.2 GBW 07436 0.042 0.03 1.29 0.95 0.74
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表 4 精密度、检出限及加标回收率测定结果
Table 4 The precisions,detection limits and spiked recoveries of the method
技术指标 V Cr Co Ni Sr RSD/% 0.5 0.7 0.4 4.2 2.3 检出限/(ng·g-1) 0.5 3.5 4.3 1.0 2.13 加标回收率/% 95.4 98.0 101.6 89.6 88.0
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