[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].

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