Electrochemical Studies of Ethoxyquin and its Determination in Salmon Samples by Flow Injection Analysis with an Amperometric Dual Detector

Abstract

Ethoxyquin (EQ) is an antioxidant widely used in the food industry. Some concerns for human health have been reported since its utilization in animal feed may lead to residues in human food such as salmon samples. This work aimed to investigate the electrochemical behavior of EQ and its major oxidation products namely a dimer of EQ (EQDM) and ethoxyquin quinone imine (EQI) by cyclic voltammetry (CV) at a carbon screen printed electrode (cSPE). The stability of these products and their reactivity against glutathione (GSH) were also studied. Oxidized products and thiol adducts were identified by a microelectrolysis of an EQ solution onto a cSPE in the absence and in the presence of GSH. The products were analyzed off‐line, by liquid chromatography coupled to a mass spectrometer (LC‐MS). One of the generated product (EQI) was shown to be highly reactive towards GSH. Based on the redox pattern of EQ, a flow injection analysis with a dual cSPE was developed in order to detect in a rapid manner EQ in salmon samples. Since matrix effects were observed, matrix‐matched calibration curves with spiked samples were built. A linear response was obtained between 20–100 μM and a limit of detection (LOD) of 7.5 μM (8.2 mg/kg of salmon). Trueness was assessed with recovery assays at three levels of concentration. The recovery was close to 100 %. Precision was determined as RSD (%) with values lower than 6 % in all cases.

Microfluidic Electrochemistry Meets Trapped Ion Mobility Spectrometry and High-Resolution Mass Spectrometry—In Situ Generation, Separation, and Detection of Isomeric Conjugates of Paracetamol and Ethoxyquin

“…To investigate whether TIMS separation is also suitable for larger conjugates, the tripeptide GSH, which is relevant in phase II metabolism, was used in the following application of our developed online chipEC-TIMS-ToF-HRMS method. With a monoisotopic mass of 307 Da, GSH is almost twice as heavy as NAC (163 Da) and has already been described in its conjugate formations with many oxidatively activated drugs. − Based on the previously shown reactions for EQI and NAC, a possible pathway for EQI and GSH is shown in Figure a, route 3, which was already postulated by Vandeput et al in 2018 . Since the TIMS separation depends on the charge, size, and shape of the investigated compound, the GSH conjugate isomers were expected to behave differently from the previously described conjugates.…”

“…The formal loss of 2 H suggests that this is an oxidation product of the formed conjugate TQ-NAC with m/z 351.1373, called EQI-NAC. This behavior has already been described by Vandeput et al 9 A possible explanation for this oxidized form is the atmospheric oxygen causing further oxidation before detection by TIMS-ToF-HRMS. Since the signal of EQI-NAC is more intense and more accessible for further experiments, the focus is placed on the EQI-NAC conjugate.…”

“…The reason for this was the lack of data on the safety of EQ and its transformation products for the consumer. In contrast to APAP, EQ and its metabolism have not yet been entirely elucidated, which is why it continues to be suspended as a feed additive, and are already in the focus of investigation by different research groups. − However, not only the metabolites but also the oxidation products, which can be formed during transport and storage times, can be dangerous for humans and the environment. − Among the most controversial transformation products of EQ are EQ-dimer (EQDM), which can accumulate in fish, and EQ quinone imine (EQI), which is highly reactive. Merel et al presented all known transformation products of EQ in 2019 .…”

An Overview of Recent Electroanalytical Applications Utilizing Screen‐Printed Electrodes Within Flow Systems

“…During the years 2018-19, nine new methods using FIA-SPE systems were developed for the determination of analytes such as isoniazid, [60] arsenic, [61] salmonella bacteria, [62] o-diphenol and its derivatives, [63] ethoxyquin, [64] glucose, [65] naproxen, [66] three tumor biomarkers, [67] acetaminophen, [68] and tryptophan and pyridoxine simultaneously. [69] Oliveira et al [62] reported a simple, low-cost, and fully disposable microfluidic FIA device for ultrasensitive Salmonella bacteria detection.…”

Capsaicinoids in Chili Habanero by Flow Injection with Coulometric Array Detection

“…Interestingly, coulometric detector is rarely used as detector for simple flow injection systems. However, flow injection methods are of particular interest for quality control as they allow to increase the amount of analyzed samples . Such electronic tongue was recently used for rapid determination of antioxidant capacity of lettuce, increasing the amount of analysis to 60 samples per hour .To the best of our knowledge, flow injection method based on coulometric array detection has never been applied for analysis of capsaicinoids in chili extracts.…”