After acidification to ca. pH 1 with sulfuric acid, commercial sugar-free tonic water is an inexpensive and readily accessible source of quinine in the appropriate concentration range for fluorescence lifetime measurements. The steps involved in the determination of the fluorescence lifetime of quinine in acidified aqueous solutions of tonic water by the time-correlated single photon counting method are outlined. Quinine fluorescence is efficiently quenched by chloride ion and fluorescence lifetimes determined as a function of added NaCl concentration are correlated via the Stern-Volmer equation. The reversion of the quenching by the chloride ion upon addition of the anionic surfactant sodium dodecyl sulfate to the solution provides insight into the phenomenon of compartmentalization in microheterogeneous media.