2-Mercaptopyrimidine-functionalized mesostructured silicas to develop electrochemical sensors for a rapid control of scopolamine in tea and herbal tea infusions

Abstract

Mesostructured silicas were synthesized and chemically functionalized with a 2-mercaptopyrimidine (MPY)-derivative. Bare and functionalized silicas (MSU-2, HMS, SBA-15, MSU-2-MPY, HMS-MPY and SBA-15-MPY) were characterized by powder X-ray diffraction, nitrogen adsorption-desorption isotherms, transmission electron and scanning electron microscopy, 29Si and 13C cross-polarization magic-angle spinning NMR spectroscopy and elemental analysis, and used to prepare modified carbon paste electrodes (CPEs). The electrodes properties were studied using potassium ferrocyanide and scopolamine as probes employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Results proved that MPY groups on the silica surface were necessary to improve the sensitivity in the voltammetric determination of scopolamine. CPE modified with HMS-MPY exhibited higher peak current toward the oxidation of scopolamine, with a well-defined oxidation peak at + 1.1 V (vs. Ag/AgCl) in DPV. This fact can be attributed to the high electroactive area of this material, with 3 D wormhole-like channel structure that favored the scopolamine diffusion. Under optimum conditions, HMS-MPY-CPE exhibited a wider linearity range, from 0.9 to 200 μM, with a detection limit of 0.3 μM and good reproducibility by DPV. The developed sensor was successfully applied for a rapid determination of scopolamine in spiked tea and herbal tea infusion samples with good recoveries (between 83 ± 5 and 101 ± 1%).