[Open-ended experiment： microextraction and smartphone-assisted colorimetric quantification of sulfur dioxide]

Open-ended experiment courses play a crucial role in cultivating practical skills， innovative thinking and scientific literacy of undergraduate students. In this project， an open-ended experiment was designed and implemented with the theme of quantitative detection of sulfur dioxide （SO₂） gas pollutants using smartphone-based colorimetry. During the experiment， volatile SO₂ in samples was enriched using headspace single-drop microextraction. In the single-drop system， SO₂ reacted with silver nanoparticles， inducing a distinct color change. SO₂ concentration was quantified through colorimetric analysis using a smartphone as a portable detection platform. This experiment guided students to employ smartphones as a novel portable detection platform， inspiring the innovative application of diverse scientific tools. The design covered fundamental analytical chemistry skills， including calibration curve construction， sample quantification and colorimetric analysis. Advanced techniques， such as microextraction and nanoparticle-mediated color reactions， were also introduced. This open-ended experiment course enables undergraduates to understand the core principles of colorimetric analysis in environmental monitoring， fostering a comprehension of the close link between theory and practical techniques in real research contexts. Throughout the experiment， students experience both the rigor and creativity of scientific exploration， while recognizing the broader significance of scientific experimentation in environmental protection， societal development and national technological advancement. Consequently， the course facilitates the internalization of scientific spirit， social responsibility and professional mission， achieving a deep integration of professional competence with values-based education.