Determination of quinine in soft drinks using the fluorometry method

Abstract

The fluorimetric method of analysis has been proposed for the qualitative and quantitative determination of the food flavoring additive quinine in the tonic water. The fluorimetric method of analysis has high sensitivity, selectivity and express speed compared to the other methods. The optimal conditions for the quinine fluorimetric determination in the soft drinks were found: solvent - 0.01 M sulfuric acid, excitation wavelength of 353 nm, luminescence wavelength of 452 nm, strobe parameters - signal delay of 0.85 μs, signal duration of 21.25 μs. To increase the sensitivity of the developed method, quinine luminescence was studied in the various concentrations of sulfuric acid from 0.005 to 1.000 M, and the quantum yield of quinine luminescence in all the investigated concentrations of sulfuric acid was calculated. It has been established that the highest quinine luminescence intensity, the highest quantum yield, and the lowest solvent background signal were observed in 0.01 M H 2 SO 4 . The influence of the related compounds of the food matrix on the fluorimetric determination of quinine was studied. It has been established that the content of such components as sugar and citric acid in the soft drinks does not affect the luminescent signal of quinine. The detection limit of quinine was calculated, which amounted to 0.0019 mg/dm 3 . In order to verify the correctness of the fluorimetric method, the results were compared with the spectrophotometric method (maximum absorption of quinine at 347 nm). The results obtained by the two methods were in good agreement, and the detection limit of the fluorimetric method was higher compared to the known works. The proposed technique could be used to control the quality and safety of the soft drinks. Keywords : quinine, fluorimetry, tonic water, luminescence quantum yield, strobe parameters. DOI: http://dx.doi.org/10.15826/analitika.2019.23.3.007 (Russian) A.А. Nikolaeva, A.A. Ivanov, E.I. Korotkova National Research Tomsk Polytechnic University, Lenina prosp., 30 Tomsk, 634050, Russian Federation