锂是重要的战略金属和新能源材料, 其开发利用受到全球的高度关注。 在高盐卤水特别是盐湖卤水和地下卤水中富含巨量的锂资源, 在对这些资源进行锂的开发利用过程中, 需对锂的含量进行准确测定, 然而卤水中共存的高浓度Na+, K+, Ca2+和Mg2+会对微量锂的准确测定产生严重的干扰。 电感耦合等离子体发射光谱法(ICP-OES)具有线性范围宽和多元素同步分析能力, 针对卤水中锂的快速准确测定, 详细开展了高盐样品中锂的ICP-OES分析方法研究。 结果表明, 锂在610.364 nm处具有较高的信噪比, 且Na+, K+, Ca2+, Mg2+和Ar不会对锂的测定产生显著的谱线干扰。 然而, 样品中大量共存的Na+, K+和Mg2+会对锂的测定产生严重的基体正干扰, 而Ca2+产生负干扰。 尽管内标法在消除基体干扰方面具有广泛的应用, 但传统的以钇和钪为内标元素的内标法不能有效解决该问题。 此外, 针对标准加入法操作繁琐、 不适合批量样品分析问题, 以及基体匹配法需多离子匹配, 且不适合样品基体组成变化的批量样品分析等问题, 考察了采用单一组分进行复杂基体匹配的可行性。 由于NaCl广泛存在于卤水中, 且对锂的测定具有显著的增敏效应, 通过系列研究发现, 通过同时向样品和标准溶液中加入10 g·L-1的NaCl, 成功解决了总量不超过40 g·L-1的NaCl, KCl和MgCl2所产生的干扰。 尽管采用该法或沉淀预分离方式均不能消除Ca2+产生的负干扰, 但当样品中Ca2+含量不高于1.8 g·L-1时, 对测定不产生显著的影响。 通过采用该方法对三种不同基体组成的卤水样品进行加标回收测定, 其回收率在96.60%~104.20%范围内。 此外, 通过与电感耦合等离子体质谱法(ICP-MS)测定结果进行对比, 充分论证了该法的准确性和可靠性(相对误差±3.66%)。 该法仅以单一的NaCl进行复杂基体匹配, 不仅简化了操作, 还实现了基体组成变化的批量样品分析, 因而在卤水中锂的快速准确测定及锂资源开发利用方面具有重要意义。

Lithium is an important strategic metal and new energy material, and its development and utilization has attracted extensive attention worldwide. There are huge amounts of lithium resources in high salinity brines especially in salt lake brines and underground brines. It is necessary to accurately determine lithium content during the development of these resources. However, high concentrations of Na+, K+, Ca2+ and Mg2+ in brines will result in serious interference with the determination of trace lithium. Inductively coupled plasma optical emission spectrometry (ICP-OES) has the ability of multi-element simultaneous analysis with wide linear range. In order to realize swift and accurate determination of lithium in brines, the analysis of lithium in high salinity samples by ICP-OES was carried out in detail in this work. Results showed that lithium has a higher signal to noise ratio at 610.364 nm, where no obvious spectral line interferences of Na+, K+, Ca2+, Mg2+ and Ar were presented for the determination of lithium. However, large amount of Na+, K+ and Mg2+ coexisting in the samples would lead to positive matrix interferences, while the Ca2+ caused negative interference. The internal standard method widely used to eliminate matrix interferences could not effectively solve this problem using whether yttrium or scandium as an internal standard element. Because the standard addition method involves complex operations and is not suitable for batch sample analysis, while the matrix matching method must match these interfering components with corresponding ions and thus is not suitable for the analysis of batch samples with different matrix compositions, the feasibility to match complex matrix with a single component was investigated in this work. Since NaCl widely exists in brines and has obviously sensitizing effect on lithium determination, we found after a series of studies that when the total amounts of NaCl, KCl, MgCl2 in samples were no more than 40 g·L-1, the interferences of these coexisting ions could be successfully solved by adding 10 g·L-1 NaCl into both the samples and the standard solutions. Although the negative interference of Ca2+ could not be effectively solved by this method or pre-separation by precipitation, it did not lead to obvious impact on the determination when its concentration was no more than 1.8 g·L-1. When this method was used for the determination of three kinds of spiked samples with different matrices, the recoveries were within the range of 96.60%～104.20%. Meanwhile, the accuracy and reliability of this developed method were also demonstrated by the comparison with these obtained by the inductively coupled plasma mass spectrometry (ICP-MS) method (The relative errors varied within ±3.66%). Only single NaCl was used in this proposed method to match different coexisting ions, by which it not only simplified the operation, but also realized the batch analysis of samples with different matrix compositions. Therefore, it has important significance for the swift and accurate determination of lithium in brines as well as for the development and utilization of lithium resources in brines.