Analysis of Dextromethorphan in Cough Drops and Syrups: A Medicinal Chemistry Laboratory

Fluorescence spectroscopy is used to determine the quantity of dextromethorphan hydrobromide (DM) in over-the-counter (OTC) cough drops and syrups. This experiment is appropriate for an undergraduate medicinal chemistry laboratory course when studying OTC medicines and active ingredients. Students prepare the cough drops and syrups for analysis, compare their results with analysis of a DM standard solution and explore interference from other ingredients (food coloring, corn syrup, and methyl cellulose). Students also perform a standard addition analysis to obtain a quantitative result for the quantity of DM in a cough medicine. This experiment can be a straightforward laboratory exercise to be completed in one laboratory period or an open-ended investigation spanning two or more laboratory periods. This exercise gives students experience in chemical analysis of an OTC medicine and could be extended to other medications or food products.