Abstract
Due to the negative impact of nitrate and nitrite on human health, their presence exceeding acceptable levels is not desired in foodstuffs. Thus, nitrite determination at low concentrations is a major challenge in electroanalytical chemistry, which can be achieved by fast, cheap, and safe electrochemical sensors. In this work, the working electrode (Au) was functionalized with p-aminothiophenol (p-ATP) and modified with gold nanoparticles (Au-NPs) to manufacture the final (Au/p-ATP-Aunano) electrode in a two-step procedure. In the first step, p-ATP was electropolymerized on the electrode surface to obtain a polyaminothiophenol (PATP) coating. In the second step, Au/p-ATP-Aunano working electrode was prepared by coating the surface with the use of HAuCl4 solution and cyclic voltammetry. Determination of aqueous nitrite samples was performed with the proposed electrode (Au/p-ATP-Aunano) using square wave voltammetry (SWV) in pH 4 buffer medium. Characteristic peak potential of nitrite samples was 0.76 V, and linear calibration curves of current intensity versus concentration was linear in the range of 0.5–50 mg·L−1 nitrite with a limit of detection (LOD) of 0.12 mg·L−1. Alternatively, nitrite in sausage samples could be colorimetrically determined with high sensitivity by means of p-ATP‒modified gold nanoparticles (AuNPs) and naphthylethylene diamine as coupling agents for azo-dye formation due to enhanced charge-transfer interactions with the AuNPs surface. The slopes of the calibration lines in pure NO2− solution and in sausage sample solution, to which different concentrations of NO2− standards were added, were not significantly different from each other, confirming the robustness and interference tolerance of the method. The proposed voltammetric sensing method was validated against the colorimetric nanosensing method in sausage samples.
Highlights
Nitrite is an approved additive to meat products as an antimicrobial flavoring and coloring agent, in addition to its ability to retard lipid peroxidation [1]
Electrochemical polymerization of an Au working electrode was achieved in two steps; the –SH groups of 4-ATP were arranged on the Au electrode surface, followed by electrochemical polymerization of the p-ATP monolayer from the –NH group end with the aid of the cyclic voltammetry (CV) technique [43]
The Au working electrode surface was coated with 10 mM p-ATP via CV within the potential range of 0–1.7 V at 20 mVs1 scanning speed for 20 cycles (Figure 1)
Summary
Nitrite is an approved additive to meat products as an antimicrobial flavoring and coloring agent, in addition to its ability to retard lipid peroxidation [1]. Another interesting property of nitrite is its capability to retard the development of rancidity during storage, to reduce the thiobarbituric acid (TBA) response (used as a measure of biooxidative status), and the subsequent warmed-over flavors (WOF) developed upon heating of meat [2,3]. Electrochemical determination of nitrite may involve both oxidation and reduction, but in actual practice, oxidation is usually preferred over reduction because cathodic nitrite measurement is prone to interference from other readily reducible species such as nitrate ion and molecular oxygen [15]. An increasing variety of nano-materials has been employed for electrochemical studies, combining the advantages of electrochemistry and nanotechnology [35,36,37,38]
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