电感耦合等离子体光谱法研究测定地热水中锂

锂是一种重要的金属材料，广泛应用于核工业、光电等行业，在经济建设中占据重要地位。地热资源是指能被人类利用的地球内部的地热能、地热流体及其矿物组分。地热水中矿物质种类丰富，我国液体锂矿储量可观。开发一种快速准确的分析测试方法，对锂矿的勘测、开发、利用具有重要的意义。电感耦合等离子体光谱法测定地热水中锂时，样品基体不会产生显著的谱线干扰，但会带来严重的基体效应。地热水中高浓度的钠、钾、钙、镁等易电离元素对锂的检测有很强的增敏作用，且四种元素在不同观测方式下增敏程度各异，轴向观测受基体干扰程度比径向更大。而且基体增敏作用不是四种离子的简单加和。实验还发现，样品基体对锂的干扰程度受雾化气流速影响很大。在较低流速下，径向观测和轴向观测下锂的回收率均随着雾化气流速的增大而减小。在中高流速下，随着雾化气流速的增大而增大。当地热水基体元素组成相差很多时，很难通过调整雾化气流速控制锂的测试准确度，不适合批量样品分析。为简便有效减小基体干扰，采用部分基体匹配法对地热水样品进行分析测试。在标准溶液和实际样品中加入一定量氯化钠溶液，可有效降低地热水基体干扰。该方法检出限与无基体标准曲线法对比，检出限并无显著增大。该方法检出限是0.20 μg·L-1（轴向）和0.41 μg·L-1（径向），无基体标准曲线法检出限是0.11 μg·L-1（轴向）和0.39 μg·L-1（径向）。通过加标回收率试验和稀释法试验验证方法准确性。三个不同基体的地热水样品加标回收率在96.5%～105.6%之间，相对标准偏差(RSD)<2％。结果与电感耦合等离子体质谱法相吻合。稀释法验证试验中，稀释样测试浓度与原样测试结果一致（±2.0%）。改进的基体匹配法可有效降低易电离元素带来的基体干扰。本方法简便、快速、高效，满足大批量地热水中锂的分析测试要求。

Investigation of Lithium Analysis in Geothermal Water by Inductively Coupled Plasma Optical Emission Spectrometry

Lithium is an important metal resource and new material, and is widely used in nuclear, photoelectric, and other industries. It occupies an important strategic position in economic construction. Geothermal resources refer to a complex, which is integrated by thermal energy, geothermal fluids and their useful minerals that humans can use. There is the considerable reserve of liquid lithium in China. It is of great significance to develop a convenient and accurate determination method ahead of lithium’s exploration, development and utilization. In determining lithium in geothermal water by inductively coupled plasma optical emission spectrometry (ICP-OES), the sample matrix does not produce significant spectral interference, but it does bring serious matrix effect. The high concentration of sodium, potassium, calcium, magnesium and other easily ionized elements in geothermal water has a strong sensitization effect on the determination of lithium. Moreover, the sensitization degree of the four elements varies with each other under different observation modes. Higher sensitization is observed in axial mode than that of radial mode. Furthermore, the apparent sensitization effect by four elements is not a simple superposition of the ionic strength. Experiments also found that the interference degree of sample matrix was greatly affected by atomization flow in both radial and axial observation modes. The lithium recovery decreased with the increase of flow at low flow rates. At medium and high flow rates, lithium recovery increased with the increase of flow. The compositions of batch geothermal water samples vary greatly, so it is not easy to control the accuracy by adjusting the atomization gas flow in lithium analysis. In order to reduce matrix interference conveniently and effectively, a modified matrix matching method was applied in this study. Single sodium chloride was added in standard solutions and geothermal water samples to match different coexisting ions. The detection limit of the proposed method was not significantly higher than that of the traditional method without matrix matching. The detection limits of the proposed method are 0.20 μg·L-1 (axial) and 0.41 μg·L-1 (radial). While those of the traditional method is 0.11 μg·L-1 (axial) and 0.39 μg·L-1 (radial). The modified method was verified by the analyte addition test and dilution test. The spiked recoveries of three geothermal water samples were 96.5% to 105.6%, with relative standard deviations lower than 2%. The results were consistent with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). The values of dilution samples agreed well with ±2.0% of the original determination. The improved matrix matching method can effectively reduce the matrix interference caused by easily ionized elements. The proposed method in this study is simplified, swift, accurate, and is suitable for batch analysis with different matrix compositions.