Pontos quânticos de carbono de Pilosocereus gounellei para determinação de taninos em chás empregando um analisador flow-batch com detecção fluorimétrica

Abstract

This work a novel new automatic flow-batch method for fluorimetric determination of tannins in teas employing carbon dots (CDs). The CDs were synthesized using a simple and easy strategy by low temperature carbonization method xiquexique (Pilosocereus gounellei) and ethanolamine were employed as precursor and functionalizer, respectively. The structural and optical properties of the CDs were investigated by the X-ray diffraction, UV-Vis, FTIR, and molecular fluorescence spectroscopy techniques. The synthesized CDs obtained a good quantum yield of 13.58% and excellent solubility in water. It was verified that the fluorescence of the CDs can be significantly reduced in the presence of tannins in green tea and black samples, in pH 8 phosphate plug. The fluorescence quenching mechanism can be attributed to the interactions between the groups present on the surface of the CDs with the tannins. For this analysis it was used the flow-batch system, with a mixing and reaction chamber, in which the excitation was made, using an ultraviolet-LED, ?max=376nm and the acquisition of fluorescence spectra on-line through a portable spectrofluorimeter as detector. The results obtained with the proposed method were compared with the reference method for tannin determination, and the detection limits and relative model deviations were estimated as being 0,102 mg L-1 e < 2.91% (n = 3) , respectively. The fluorescence intensity of Tannins-CDs showed a linear response with tannin concentration in the range of 2.0 to 30 mg.L-1 with r2 = 0.996, and a very satisfactory analytical frequency (18.9 h -1).