[Case-based teaching with both positive and negative examples in undergraduate analytical chemistry laboratory： determination of six nitrogen-containing pesticides in environmental samples by solid-phase microextraction-high performance liquid chromatography].

内容摘要

In analytical chemistry， separation and enrichment steps serve not only as critical stages in the analytical workflow， but also as core technologies that determine the accuracy， reliability， and applicability of analytical methods. However， in conventional experimental instruction， this step is frequently overlooked owing to time constraints and an overemphasis on instrumental techniques， leading to fragmented knowledge structures and hindering the development of integrated analytical thinking that connects theory with practice. To address this issue， this study， based on the "knowledge-ability-practice" three-dimensional integrated teaching objective， innovatively establishes a "positive-negative case-based teaching" model， using the solid-phase microextraction （SPME） of six nitrogen-containing pesticides from environmental water samples as the instructional case. By comparing fibers coated with non-polar polydimethylsiloxane （PDMS） and strongly polar polyacrylate （PA）， and employing high performance liquid chromatography with ultraviolet detection （HPLC-UV）， this study systematically investigates the matching relationship between analyte polarity and coating properties. In the positive case， the PDMS coating demonstrates superior extraction performance for weakly polar pesticides based on the "like dissolves like" principle， with a linear coefficient of determination R2≥0.993 7 and detection limits ranging from 0.019 to 0.17 μg/L. In contrast， in the negative case， the PA coating shows weaker extraction efficiency due to differences in the extraction mechanism， yielding detection limits between 0.066 to 1.069 μg/L. Based on spiked recovery tests conducted on actual river water samples from Lanzhou （recoveries： 81.5% to 117%）， a multi-dimensional evaluation system of "knowledge internalization， competency enhancement， and practical literacy" is established accordingly. Teaching feedback demonstrates that the students show a marked improvement in their understanding of the core principles， and their innovative thinking and problem-solving skills are effectively cultivated. The "contrasting-case-based" pedagogical approach effectively bridges theory and experiment while stimulating students' investigative thinking. The study provides a replicable and scalable practical model for the reform of analytical chemistry experimental teaching， which holds significant value in cultivating high-caliber talents with rational method selection and problem-solving abilities. 分析化学中的分离与富集步骤不仅是分析流程的关键环节，更是决定分析方法准确性、可靠性及适用性的核心技术。然而，在传统实验教学中，该环节常因课时限制和教学重心偏重仪器操作而遭到忽视，导致学生知识体系呈现“碎片化”，难以建立理论联系实际的完整分析科学思维。为解决这一问题，本文立足“知识-能力-实践”三维融合的教学目标，以固相微萃取（SPME）技术萃取环境水样中6种含氮农药为案例，创新性构建“正反案例式教学”模式。通过对比非极性聚二甲基硅氧烷（PDMS）涂层与强极性聚丙烯酸酯（PA）涂层的纤维，采用高效液相色谱-紫外检测法（HPLC-UV），系统探究分析物极性与涂层性质的匹配规律：正向案例中PDMS涂层基于“相似相溶”原理，对弱极性农药展现出更优的萃取性能（线性决定系数R2≥0.993 7，检出限0.019~0.17 μg/L）；反向案例中PA涂层因萃取机理差异，萃取效果较弱（检出限0.066~1.069 μg/L）。结合对兰州市实际河流水样的加标回收试验（加标回收率为81.5%~117%），同步建立“知识内化-能力提升-实践素养”多维度评估体系。教学反馈显示，学生对核心原理的理解显著深化，创新思维与问题解决能力得到有效培养。“正反案例对比”教学能够有效衔接理论与实验、激发学生探究思维，为分析化学实验教学改革提供了可复制、可推广的实践范例，对培养具备理性方法选择与问题解决能力的高素质人才具有重要价值。