Pan Yifan, Zhang Feng, Gao Wei, Sun Yuelun, Zhang Sen, Lian Hongzhen, Mao Li
State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry & Chemical Engineering, Center of Materials Analysis, Nanjing University, Nanjing 210023, China.
Ministry of Education (MOE) Key Laboratory of Modern Toxicology, School of Public Health, Nanjing Medical University, Nanjing 211166, China.
Se Pu. 2022 Nov;40(11):979-987. doi: 10.3724/SP.J.1123.2022.07013.
Metal and metalloid elements have various possible isotopic compositions and oxidation states and often form coordination or covalent compounds with inorganic and organic small molecules or biological macromolecules, resulting in complex elemental speciation. Different species of the same element often have different properties, which dictate their behavior. Thus, elemental speciation analysis is vital for comprehensively and accurately assessing an element's environmental and biological effects and the corresponding risks. Because elemental speciation determines the behavior of an element in different environmental and biological processes, the analysis of elemental species has, in recent years, been important in various subjects, including analytical chemistry, environmental chemistry, geochemistry, ecology, agronomy, and biomedicine. The complexity of environmental and biological sample matrices, as well as the multiformity, low levels, and lability of chemical forms pose severe challenges in elemental speciation analysis. Therefore, the highly selective identification and efficient separation of native species is necessary for conducting the identification, quantification, ecotoxicity evaluation, and physiological function study of elemental speciation. Sample pretreatment by solid-phase extraction is an effective solution to the aforementioned problems, but the existing methods do not meet the requirements of current research. The transition of the target species from pre-processing to the detection device includes both on- and off-line arrangements. Compared with the on-line approach, the off-line approach requires more manual participation, increasing the analysis workload. However, the off-line approach can improve the analysis efficiency through high-throughput pretreatment when large batches of samples are encountered, meaning the off-line approach is still an effective model. Ion imprinting technology has been developed based on existing molecular imprinting technology, with four main steps present in the synthesis of ion imprinted polymers. First, ion imprinting technology uses metal ions as templates. Then, these templates are combined with the functional monomers through coordination, electrostatic or hydrogen bonding. The functional monomers simultaneously surround and fix the templates, after which the cross-linkers and functional monomers polymerize to prepare ion-imprinted polymers with a specific structure and composition. Finally, the imprinted holes are created in the polymers by eluting the template ions. Therefore, the template molecules, functional monomers, and cross-linkers are three precursors necessary for synthesizing ion-imprinted polymers. These polymers can specifically bind to the imprinted metal ions with accuracy, sensitivity, and reliability. In recent years, they have been widely used in separating, enriching, analyzing, and detecting elemental species. During solid-phase extraction, the non-magnetic adsorbent materials dispersed in the sample solution need to be separated by centrifugation or filtration, which is time-consuming and laborious. Because an external magnetic field can be used for rapid magnetic solid-phase extraction, it has become a potential method for separating and enriching elemental species. This review systematically summarizes the latest progress in ion-imprinting technology, including its principle and the preparation methods of ion-imprinted polymers. The challenges faced by ion imprinting technology are analyzed in the context of the development of ion-imprinting magnetic solid-phase extraction in elemental speciation analysis. Finally, the direction of future development and the strategies of ion imprinting technology in elemental speciation analysis are proposed. It is important to exploit novel organic-inorganic hybrid polymerization-based multifunctional ion-imprinted magnetic nanocomposites for the magnetic solid-phase extraction and separation of elemental species. By establishing the pretreatment protocols with high recognition selectivity, strong separation ability, large adsorption capacity, and good speciation stability, we expect to achieve the research objectives of simultaneously separating and enriching the multiple-species of typical metal/metalloid elements in environmental and biological samples.
金属和类金属元素具有多种可能的同位素组成和氧化态，并且常常与无机和有机小分子或生物大分子形成配位或共价化合物，从而产生复杂的元素形态。同一元素的不同形态通常具有不同的性质，这些性质决定了它们的行为。因此，元素形态分析对于全面、准确地评估元素的环境和生物效应以及相应风险至关重要。由于元素形态决定了元素在不同环境和生物过程中的行为，近年来，元素形态分析在包括分析化学、环境化学、地球化学、生态学、农学和生物医学等多个学科中都具有重要意义。环境和生物样品基质的复杂性，以及化学形态的多样性、低含量和易变性，给元素形态分析带来了严峻挑战。因此，对于元素形态的鉴定、定量、生态毒性评估和生理功能研究而言，对天然形态进行高选择性鉴定和高效分离是必要的。通过固相萃取进行样品预处理是解决上述问题的有效方法，但现有方法无法满足当前研究的要求。目标形态从预处理到检测装置的转移包括在线和离线两种方式。与在线方式相比，离线方式需要更多的人工参与，增加了分析工作量。然而，当遇到大批量样品时，离线方式可以通过高通量预处理提高分析效率，这意味着离线方式仍然是一种有效的模式。离子印迹技术是在现有的分子印迹技术基础上发展起来的，离子印迹聚合物的合成主要包括四个步骤。首先，离子印迹技术以金属离子为模板。然后，这些模板通过配位、静电或氢键与功能单体结合。功能单体同时围绕并固定模板，之后交联剂与功能单体聚合，制备具有特定结构和组成的离子印迹聚合物。最后，通过洗脱模板离子在聚合物中形成印迹孔。因此，模板分子、功能单体和交联剂是合成离子印迹聚合物所需的三种前体。这些聚合物能够以准确、灵敏和可靠的方式特异性结合印迹金属离子。近年来，它们已广泛应用于元素形态的分离、富集、分析和检测。在固相萃取过程中，分散在样品溶液中的非磁性吸附材料需要通过离心或过滤进行分离，这既耗时又费力。由于可以利用外部磁场进行快速磁性固相萃取，它已成为一种分离和富集元素形态的潜在方法。本综述系统总结了离子印迹技术的最新进展，包括其原理和离子印迹聚合物的制备方法。在元素形态分析中离子印迹磁性固相萃取的发展背景下，分析了离子印迹技术面临的挑战。最后，提出了离子印迹技术在元素形态分析中的未来发展方向和策略。开发基于新型有机 - 无机杂化聚合的多功能离子印迹磁性纳米复合材料用于元素形态的磁性固相萃取和分离具有重要意义。通过建立具有高识别选择性、强分离能力、大吸附容量和良好形态稳定性的预处理方案，我们期望实现同时分离和富集环境和生物样品中典型金属/类金属元素多种形态的研究目标。
