Extraction, purification, and spectroscopic characterization of a mixture of capsaicinoids

This laboratory experiment provides a safe and effective way to instruct undergraduate organic chemistry students about natural-product extraction, purification, and NMR spectroscopic characterization. On the first day, students extract dried habañero peppers with toluene, perform a pipet silica gel column to separate carotenoids from capsaicinoids, and perform thin-layer chromatography. On the second day, students characterize their mixture of capsaicinoids, approximating the relative quantities of the two primary capsaicinoids, capsaicin and dihydrocapsaicin, by NMR. Additionally, students are introduced to 2D NMR analysis. The effectiveness of the laboratory is assessed by two methods: a qualitative postlab student self-assessment and a quantitative pre- and postlab test. For the qualitative assessment, students stated that they acquired an improved understanding of NMR from the experiment. Accordingly, the total average on the quantitative prelab and postlab 8-point test increased from 3.43 ± 1.62 (SD) to 4.25 ± 1.48 (SD) and demonstrated a statistically significant improvement (p value of 0.001), as did the average for the 5-points of NMR-related questions in the prelab- and postlab 8-point test: 1.61 ± 1.21 (SD) to 2.13 ± 1.11 (SD), with p value of 0.004.