On-line Determination of Hg (Ⅱ) in Geological Samples by AFS after Solid Phase Extraction Using Dithizone-modified Graphene Oxide/Chitosan Composite Microspheres
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摘要: 汞可以指示矿床或矿化存在，是一种重要的地质过程示踪元素，因此汞的测定是十分重要的。由于汞在地质矿床中丰度较低，直接测定存在困难，需要进行预分离富集处理。目前采用的分离富集手段大多数是离线，自动化程度较低。本文将合成的双硫腙改性氧化石墨烯/壳聚糖复合微球制成固相萃取小柱，考察了溶液pH、吸附剂种类和体积对汞的吸附效果的影响，优化了固相萃取在线采样/洗脱时间和速率对汞的吸附/洗脱效果的影响，建立了固相萃取在线富集-原子荧光光谱法测定地质样品中痕量汞的分析方法。结果表明：溶液pH=3.0时，以5 mL/min的采样速率进样5 min，汞的吸附率大于90%；用20 g/L硫脲-1.0 mol/L硝酸混合溶液作洗脱液，以1 mL/min的洗脱速度洗脱1 min，洗脱率大于95%。汞含量在0.050~5.0 μg/L范围内线性关系良好，富集因子为22，检出限为0.0019 μg/L。采用本方法测定了土壤和沉积物国家标准物质样品，Hg的测定值与参考值的相对误差小于±13%。与离线分析相比，本方法具有灵敏度高、操作简单快速等特点。Abstract: Mercury can indicate the presence of deposits or mineralization, which is an important tracer element of geological processes, thus making the determination of mercury very important. Due to the low abundance of mercury in ore deposits, it is difficult to directly determine and thus pre-separation enrichment is needed. Presently, most of the separation and preconcentration methods are off-line with a low degree of automation. Graphene oxide/chitosan microspheres modified by dithizone were prepared and applied as adsorption materials for solid phase extraction column. The effect of experimental parameters including acidity, adsorbent type, and adsorption volume on the absorption efficiency was evaluated. Sampling/elution time and the sampling/elution rate during solid phase extraction were optimized. Based on these conditions, an analytical method for the determination of trace mercury in geological samples by on-line enrichment-atomic fluorescence spectrometry with solid phase extraction was established. The results show that when the pH value is 3.0, the adsorption rate of mercury is more than 90% at 5 mL/min sampling rate. The elution rate was >95% when 20 g/L of thiourea and 1.0 mol/L HNO3 were used as elution solution and elution for 1 min at the rate of 1 mL/min. The working curve showed a good linear relationship when the concentration was between 0.050 μg/L and 5.0 μg/L. The enrichment factor was 22 and the detection limit was 0.0019 μg/L. The relative error of the measured value of Hg and the reference value was less than ±13% when this method was used to determine soil and sediment national standard materials. Compared with the off-line analysis, this method has advantages such as high sensitivity and simple operation.
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表 1 不同洗脱剂对汞的洗脱效果
Table 1. Elution effect of different elution agents on mercury
洗脱剂 汞的洗脱率(%) 2.0 mol/L硝酸 2.25 50 g/L硫脲 10.34 50 g/L硫脲-0.5 mol/L盐酸 47.63 50 g/L硫脲-1.5 mol/L盐酸 38.05 20 g/L硫脲-1.0 mol/L硝酸 91.25 40 g/L硫脲-1.0 mol/L硝酸 40.05 50 g/L硫脲-1.0 mol/L硝酸 60.70 
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表 2 实际地质样品中汞含量的分析结果
Table 2. Analytical results of mercury in geological samples
标准物质编号 Hg含量的参考值(μg/g) Hg含量的测量值(μg/g) 相对误差(%) GBW07447 0.015 0.015 0.0 GBW07449 0.008 0.009 12.5 GBW07450 0.020 0.018 -10.0 GBW07303 0.050 0.046 -8.0 GBW07305 0.100 0.090 -10.0
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