Supercritical fluid extraction versus traditional solvent extraction of caffeine from tea leaves: A laboratory-based case study for an organic chemistry course

摘要

In this case-based laboratory, an instrument sales person attempts to convince an analysis laboratory of the virtues of supercritical fluid extraction (SFE). The sales person deals directly with the laboratory technicians who will make the decision. Arrangements are made to have SFE instrumentation brought into the laboratory for a comparative study. The extraction and gravimetric determination of caffeine from finely cut tea leaves is chosen as the "test". The technicians are divided into two groups. Group A performs a traditional solvent extraction using methylene chloride (CH _2Cl _2)/alkaline water and group B using a SFE method. Students play the role of laboratory technicians and use the data collected to determine which method they would choose considering several variables and issues. It puts the student into a real-world situation and requires them to apply their critical-thinking skills to make a decision. This case-based laboratory exposed second-year science students to a new technology, provided them with an opportunity to compare and contrast competitive methods, and promoted green chemistry initiatives. An unexpected instrument anomaly affected several students in Group B. How this anomaly was reflected in student assessment of this case-based laboratory is also presented.