A metal-organic framework-based amperometric sensor for the sensitive determination of sulfite ions in the presence of ascorbic acid

A carbon paste electrode modified with the MIL-101(Cr) metal-organic framework (MIL-101(Cr)-CPE) was prepared, characterized and assayed to the voltammetric detection of sulfite ions. Electrochemical impedance spectroscopy and cyclic voltammetry indicated a significant increase in charge transfer ability and real surface area (R-ct = 1.1 k Omega and S = 0.220 cm(2)) of the MIL-101(Cr)-CPE in comparison with the bare CPE (R-ct = 7.8 k Omega and S = 0.031 cm(2)). It was demonstrated by cyclic voltammetry that the oxidation of sulfite ions at the MIL-101 (Cr)-CPE follows an irreversible and diffusion-controlled mechanism. Also, the peak current of sulfite ions was 1.5-fold more intense on MIL-101(Cr)-CPE compared to the unmodified CPE. An analytical method was therefore developed, based on square wave voltammetry: under optimized experimental conditions, the MIL-101(Cr)-CPE electrode displayed a linear relationship between the oxidation peak current and the concentration of sulfite in the concentration range of 2 mu M-70 mu M, with a detection limit of 0.58 mu M (S/N = 3). The sensor was furthermore exploited for the simultaneous determination of sulfite and ascorbic acid, which gave well separated anodic peak at 0.35 V and 0.90 V (vs. Ag/AgCl, 3 M KCl), respectively. The proposed method was further used to determine both analytes in commercial wines, thus establishing its applicability as inexpensive analytical tool for quality control.

Automated summary

The carbon paste electrode modified with the MIL-101(Cr) metal-organic framework showed improved charge transfer ability and increased real surface area, resulting in a more intense oxidation peak current of sulfite ions compared to the unmodified electrode. A linear relationship between the oxidation peak current and sulfite concentration was established, with a detection limit of 0.58 μM in the range of 2 μM-70 μM.