Fluorescence Analysis of Quinine in Commercial Tonic Waters

Quinine is known for treating malaria, muscle cramps, and, more recently, has been used as an additive in tonic water due to its bitter taste. However, it was shown that excessive consumption of quinine can have severe side effects on health. In this work, we utilized fluorescence spectroscopy to measure the concentration of quinine in commercial tonic water samples. An external standard method was used to calculate the concentrations of quinine in two commercially available tonic water brands, namely Canada Dry and Schweppes, and compare them to the maximum allowable concentration of quinine in beverages. Upon analysis of the data collected by five different groups, the levels of quinine were found to be above the average concentration in most commercial tonic water samples, but below the maximum permitted concentration. Moreover, the five replicate sets of data demonstrated high reproducibility of the method employed in this study. The simple yet instructive protocol that we developed can be adapted to determine the concentration of other fluorescent compounds in foods and beverages. Further, the presented method and detailed protocol can be easily adopted for undergraduate labs and in chemical education.