Líquidos iônicos próticos: propriedades, ecotoxicidade e aplicações na eletroquímica

Abstract

The class of protic ionic liquids (LIPs) has attracted interest in the last decade due to their simple and low-cost synthesis route and, mainly, their physicochemical properties. The application of LIPs as supporting electrolytes in electroanalytical applications is reported for the first time in this research. The analytes were caffeine (CAF) and nicotine (NIC), which are emerging contaminants and are among the most consumed substances in the world. In the first chapter of the results of this work, the correlation between intermolecular interactions of hydrogen bond donor groups and the impact of carbon chain length on thermal stability and viscosity were investigated, in addition to the electrochemical stability and ecotoxicity associated with LIPs derived from organic acids combined with the 2-hydroxyethylammonium cation. The structures and purities of LIPs were confirmed by FTIR, NMR, CHN, UHRMS, and water content. In the second results chapter, an alternative electrolyte, 2- hydroxyethylammonium acetate (2HEAA), was used in the development of an electroanalytical method for the simultaneous determination and quantification of CAF and NIC, through differential pulse voltammetry (DPV). The system with the 2HEAA electrolyte was characterized by electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy - EIS), highlighting the lower resistance with RCT of 312 Ω in relation to the conventional electrolyte (2100 Ω), in addition to the better definition of the voltammogram profile of the analytes and lower background current. The DV parameters were optimized for the best conditions (current intensity and width at half height) for method development. The method was validated from the calibration curves obtained, which presented LOD of 0.82 and 6.26 μmol L-1 and LOQ of 2.73 and 20.8 μmolL-1 CAF and NIC, respectively. The system showed adequate precision and selectivity, obtaining values lower than 10% of the relative standard deviation. The method was used to determine the analytes in fortified samples, obtaining recoveries between 87.25 and 111.40%. 2HEAA demonstrated high efficiency as an alternative electrolyte with a good signal-to-noise ratio, and increased analytical sensitivity of the method, in addition to presenting low cost and rapid preparation of the electrolyte.