Caffeine determination in beverages by voltammetry with the carbon-containing electrodes modified with aryldiazonium salts

The method of carbon containing electrode ( CCE ) modification with tosylated arendiazonium salts ( ADT ) was proposed for the voltammetric ( VA ) determination of caffeine in beverages. The comparison of chemical spontaneous and electrochemical modification approaches was carried out for ADT modified CCE for VA caffeine determination for the first time. A new class of ADT is characterized by high solubility and stability for one month that plays significant role in the process of electrode surface modification. Salts with nitro and carboxy substituents were tested. The optimal conditions for the spontaneous chemical modification of the CCE were selected: ADT modifier with NO 2 substituent, electrode immersion time in the modifier solution for 10 seconds, modifier concentration of 5 mg / dm 3 . ADT deposition on the electrode surface was confirmed by the IR spectroscopy and scanning electron microscopy with the formation of covalent bonds between the carbon atoms of electrode surface and the benzene rings of the modifier. It was shown that the electroactive surface area increases by two times after the modification. Consequently, the technique sensitivity increasing the detection limit of 51 mg / dm 3 and linear range extension from 154 up to 500 mg / dm 3 was observed. While applying the modified electrode, the analysis time was reduced to 15 minutes. Furthermore, the suitability of CCE modified with NO 2 substituent was tested for the analytical purposes. As a result, the caffeine was determined in some tonic and carbonated drinks. The comparison of the results obtained by the proposed method with ADT modified CCE and the level declared by the manufacturer was carried out. The high compliance was established. In addition, the obtained data was consistent with the results by the independent spectrophotometric method. Keywords : caffeine, diazonium aromatic salts, modifier, carbon-containing electrode, voltammetry, spontaneous modification, SEM, IR spectroscopy, cyclic voltammetry DOI: http://dx.doi.org/10.15826/analitika.2020.24.1.007 E.V. Dorozhko, A.O. Gusar, E.A. Bedareva, G.B. Slepchenko, M.E. Trusova, E.I. Korotkova  National Research Tomsk Polytechnic University, Lenina prosp., 30, Tomsk, 634050, Russian Federation