Sulfite food additive electrochemical determination by nucleophilic addition on poly(4-aminodiphenylamine)-4-aminothiophenol-Au composite electrode

Abstract

Realizing reagentless selective sodium sulfite (SO32−) food-additive sensors for real-time applications is challenging. Regular SO32− additive monitoring is necessary for providing harmless food to consumers. In this study, Au nanoparticles were prepared by electrodepositing Au3+ (+0.75 V vs. saturated calomel electrode) on a glassy carbon (GC) surface. An Au/GC surface self-assembled 4-aminothiophenol (4-ATP) (denoted as 4-ATP-Au/GC). The 4-ATP head group (-SH) was chemisorbed on S-Au/GC, while tail –NH2 was functionalized using 4-aminodiphenylamine (ADPA) via a chemical/electrochemical approach. The as-prepared p-ADPA-4-ATP-Au/GC was thoroughly investigated stepwise by cyclic voltammetry traces and ex situ spectroscopy. We propose an E→CE→-mechanism-based SO32− determination: p-ADPA-4-ATP-Au/GC was electrochemically oxidized to a quinonimine unit and chemically sulfonated by the nucleophilic addition reaction by SO32−. This product was further electrochemically oxidized. The sulfonation of the polymer chains was confirmed using ex situ X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy. The p-ADPA-4-ATP-Au/GC composite electrode exhibited a wide linear range of SO32− detection, from 5 to 160 μM. The sensitivity and detection limit were 0.0176 μA μM−1 and 1.5 μM, respectively. Finally, the p-ADPA-4-ATP-Au/GC was used in food samples containing SO32−, which yielded a recovery in the range of 101.3–102.6%.