Liquid chromatography-electrochemical detection for the determination of ethoxyquin and its dimer in pear skin and salmon samples

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

Over the last 3 decades, electrochemistry (EC) has been successfully applied in phase I and phase II metabolism simulation studies. The electrochemically generated phase I metabolite-like oxidation products can react with selected reagents to form phase II conjugates. During conjugate formation, the generation of isomeric compounds is possible. Such isomeric conjugates are often separated by high-performance liquid chromatography (HPLC). Here, we demonstrate a powerful approach that combines EC with ion mobility spectrometry to separate possible isomeric conjugates. In detail, we present the hyphenation of a microfluidic electrochemical chip with an integrated mixer coupled online to trapped ion mobility spectrometry (TIMS) and time-of-flight high-resolution mass spectrometry (ToF-HRMS), briefly chipEC-TIMS-ToF-HRMS. This novel method achieves results in several minutes, which is much faster than traditional separation approaches like HPLC, and was applied to the drug paracetamol and the controversial feed preservative ethoxyquin. The analytes were oxidized in situ in the electrochemical microfluidic chip under formation of reactive intermediates and mixed with different thiol-containing reagents to form conjugates. These were analyzed by TIMS-ToF-HRMS to identify possible isomers. It was observed that the oxidation products of both paracetamol and ethoxyquin form two isomeric conjugates, which are characterized by different ion mobilities, with each reagent. Therefore, using this hyphenated technique, it is possible to not only form reactive oxidation products and their conjugates in situ but also separate and detect these isomeric conjugates within only a few minutes.

Analysis of synthetic antioxidants in salmon silage using QuEChERS extraction method followed by determination by LC-MS/MS; a single-laboratory validation study

A new method was developed and in-house validated to determined ethoxyquin (EQ), butylated hydroxyanisole (BHA) and propyl gallate (PG) in fish silage and fish oil used for production of animal feed. Sample pre-treatment comprises use of QuEChERS (quick, easy, cheap, effective, rugged and safe) extraction and gives extracts for liquid chromatography-triple quadrupole mass spectrometry analysis without matrix interferences. The results allow quantification of the antioxidants in all matrices by using deuterated internal standards and calibration curves made in solvent, as well as establishing low detection limits (0.012-0.015 mg/kg) and quantification limits (0.040-0.050 mg/kg) needed regarding the recent suspension of EQ as feed additive within the European Union. The proposed method was validated in terms of linearity, accuracy (relative error, ±1.4%), precision (RSD, ≤2.7%) and recovery (matrix effect, 97-101%) where all the parameters show acceptable results according to recognized guidelines (including EuraChem) within method validation. Combined expanded measurement uncertainty was estimated with a coverage factor of 2 by including all contributors to analytical variation, showing results of ±15% or better. The combined QuEChERS and LC-MS/MS method was successfully applied to salmon silage samples and their corresponding aqueous and oil fractions.

Analysis of ethoxyquin and its oxidation products in swine tissues by gas chromatography-tandem mass spectrometry for evaluating the feed-to-animal tissue transfer of ethoxyquin and its metabolites

BACKGROUND

Ethoxyquin (EQ) is a common antioxidant which is widely used in animal feed. But the supplement of EQ in animal feed may lead to the residues of EQ and its major oxidation products: ethoxyquin quinone imine (EQI) and ethoxyquin dimer (EQDM) in animal tissue. Thus, it would pose potential health hazards to consumers. However, the method for the simultaneous determination of EQ, EQI and EQDM in animal tissues is currently not available, and the accumulation extend of these chemicals in animal tissues after EQ administration remains to be evaluated.

RESULTS

A gas chromatography-tandem mass spectrometry method was successfully developed for the simultaneous determination of EQ, EQI and EQDM in swine tissues. The quantitative limits of EQ, EQI and EQDM can achieve to 0.5, 5.0 and 5.0 μg/kg in swine tissues, respectively. The spiked-recovery ratios of the three analytes (5-2000 μg/kg) were in the range of 64.7%-100.7% with relative standard deviations below 11.6%. Moreover, the utilization of this method for the analysis of actual swine tissue samples revealed that the application of commercial EQ additive in swine diet would produce the residues of all the three chemicals (EQ, EQI and EQDM) in fat, kidney, liver and muscle.

CONCLUSIONS

The assay accuracy and precision of this GC-MS/MS method can meet the requirement of quantitative analysis. Meanwhile, the safety of EQ as a feed additive should be seriously considered with regard to food safety concerns since the oxidation product of EQ may have potential carcinogenicity.

Ultrasensitive bio-detection using single-electron effect

Single-electron devices are capable of detecting changes of the electric field caused by the presence of one single electron in their environment. These devices are optimized to identify the material that is in close contact with them based on the material's internal charge distribution or dipole moment. As an important practical use, they present the possibility of detecting bacteria, viruses, or pathogens. However, their practical use is hampered by their nano-meter size, which is normally an order of magnitude smaller than that of detected species, their very complex fabrication techniques, their cryogenic operational temperature, and the problem of bringing the said species in contact with the single-electron structure. In this document, a large scaled room temperature single-electron structure is introduced, and its ability to distinguish liquids based on their internal dipole moments is demonstrated. The device is a Schottky junction made of PtSi, as the metal contact, and the walls and surfaces of the porous Si, as the semiconductor. The reverse bias current-voltage (IV) characteristic of this device is sensitive to 1 ppm change in the dipole moment of the liquid entering its pores. The simple fabrication, easy testing procedure, high sensitivity, and fast response can make this device an optimized testing kit to identify the given bacteria, viruses, or pathogens dissolved in liquids.

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Using single-electron phenomenon to detect minute changes in electric fields.

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Simple and fast Measurement for detection of liquids and suspensions.

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High sensitivity to electric fields at room temperature.

A Review on Recent Advances in the Applications of Boron-Doped Diamond Electrochemical Sensors in Food Analysis

The usage of boron-doped diamond (BDD) material has found to be very attractive in modern electroanalytical methods and received massive consideration as perspective electrochemical sensor due to its outstanding (electro)chemical properties. These generally known facilities include large potential window, low background currents, ability to withstand extreme potentials and strong tendency to resist fouling compared to conventional carbon-based electrodes. As evidence of superiority of this material, couple of reviews describing the overview of various applications of BDD electrodes in the field of analytical and material chemistry has been reported in scientific literature during last decade. However, herein proposed review predominantly focuses on the most recent developments (from 2009 to 2020) dealing with the application of BDD as an advanced and environmental-friendly sensor platform in food analysis. The main method characteristics of analysis of various organic food components with different chemical properties, including additives, flavor and aroma components, phenolic compounds, flavonoids and pesticides in food matrices are described in more details. The importance of BDD surface termination, presence of sp² content and boron doping level on electrochemical sensing is discussed. Apart from this, a special attention is paid to the evaluation of main analytical characteristics of the BDD electrochemical sensor in single- and multi-analyte detection mode in food analysis. The recent achievements in the utilizing of BDD electrodes in amperometric detection coupled to flow injection analysis, batch injection analysis, and high-performance liquid chromatography are also commented. Moreover, actual trends in sample preparation techniques prior to electrochemical sensing in food analysis are referred.

Analysis of ethoxyquin residues in animal feed using QuEChERS and gas chromatography tandem mass spectrometry and its results from Catalonian production 2018-2019

Ethoxyquin (EQ) is a quinolone commonly used as an antioxidant additive and a fungicide. However, Regulation (EU) 2017/962 suspended its authorisation as a feed additive for all animal species and categories. The aim of this study is thus to ensure compliance with this regulation by developing a method of analysing EQ in animal feed. For analysis, EQ was extracted from animal feed by using a modified QuEChERS protocol that used an ascorbic acid buffer to minimise its degradation. The extracts were analysed by gas chromatography coupled to triple quadrupole mass spectrometry (GC-QQQ), obtaining two chromatographic peaks corresponding to EQ and its transformation products. A study of these peaks was subsequently carried out using different standards, evincing that EQ had indeed been converted into several different transformation products. Quantification required the sum of the areas of the different peaks. The method was validated according to European Commission guidelines, namely SANTE/12682/2019. The obtainment of pesticide-free samples for carrying out the validation process was a critical achievement, as EQ residues were detected in 90% of the analysed samples. This was made possible by manufacturing 20 different feed samples from a mixture of several cereals used in animal feed in the laboratory. Method validation yielded excellent results in terms of accuracy (recoveries 70-120%), precision (RSD < 20%) and linearity (r²≥ 0.99) at the studied levels, as well as excellent sensitivity and selectivity (retention time ±0.1 min; ratio < 30%) to the LoQ. Over the course of 2018 and 2019, 70 samples of various feed matrices from agricultural production in Catalonia were analysed, garnering positive results 43% of the time.

Development of a human biomonitoring method for assessing the exposure to ethoxyquin in the general population

Ethoxyquin (EQ) is commonly used as an antioxidant in animal feeds. Although EQ is not permitted for usage in food products for humans within the EU, residues of EQ and its transformation products could be determined in food of animal origin. Despite its widespread use and concerns on its toxicological profile, no information about the systemic exposure to EQ in the general population is available. Hence, we developed a human biomonitoring (HBM) method for EQ. Our approach included a metabolism study with five subjects, who were administered an oral dose of 0.005 mg EQ/kg body weight. Unchanged EQ and the major metabolite 2,2,4-trimethyl-6(2H)-quinolinone (EQI) were identified as urinary excretion products of EQ. While small amounts of EQ could be determined in high concentrated samples from the metabolism study only, 28.5% of the orally applied EQ dose could be recovered as EQI. Toxicokinetic parameters were determined for EQI, the potential biomarker of exposure. In addition, an analytical method for EQI (LOQ = 0.03 µg/L) in urine based on UHPLC-MS/MS comprising enzymatic glucuronide hydrolysis and salt-assisted liquid-liquid extraction was developed, validated and applied to 53 urine samples from the general population. EQI could be quantified in 11 (21%) of the samples in levels up to 1.7 µg/L urine, proving the suitability of the developed method for the intended purpose.

A new alternative assay for sensitive analysis of ethylenethiourea and propylenethiourea in fruit samples after their separation

Ultra-high-performance liquid chromatography (UHPLC) coupled with a cobalt phthalocyanine screen-printed carbon electrode (CoPc-SPCE) was developed and validated for quantitative analysis of ethylenethiourea (ETU) and propylenethiourea (PTU). CoPC-SPCE provided high catalytic properties for ETU and PTU oxidation. This fabricated electrode is inexpensive, disposable, and easy to prepare by an in-house screen-printing technique. The chromatographic separation was performed in isocratic mode on a reversed phase C18 (100 mm × 4.6 mm, 3 μm) column, using a 90 : 10 (v/v) ratio of 0.05 M phosphate buffer solution (pH 4) and methanol as the mobile phase with a flow rate of 1.0 mL min^-1 at an oxidation potential of +0.7 V vs. Ag/AgCl. The separation could be achieved within 3 min, and a wide linear range of 0.01-100 μg mL^-1 (r² > 0.99) was obtained for both analytes. The limits of detection (3 S/N) were found to be 0.006 and 0.009 μg mL^-1 for ETU and PTU, respectively. Furthermore, this proposed method was utilized to determine ETU and PTU in fruit samples with satisfactory results, yielding excellent intra-day and inter-day relative standard deviations and recoveries. These results demonstrated that the proposed assay can be used as a new alternative way for inexpensive, rapid, selective and sensitive determination of ETU and PTU in fruit samples.

Analytical methods to analyze pesticides and herbicides

Presented in this paper is an annual review of literatures published in 2018 on topics relating to analytical methods for pesticides and herbicides. According to the different techniques, this review is divided into six sections, including extraction methods; chromatographic or mass spectrometric techniques; electrochemical techniques; spectrophotometric techniques; chemiluminescence and fluorescence methods; and biochemical assays. PRACTITIONER POINTS: Totally 134 relevant research articles are summarized. The review is divided into six parts according to the techniques. Chromatographic and mass spectrometric methods are the most widely used.

Determination of the Synthetic Antioxidant Ethoxyquin and Its Metabolites in Fish and Fishery Products Using Liquid Chromatography-Fluorescence Detection and Stable-Isotope Dilution Analysis-Liquid Chromatography-Tandem Mass Spectrometry

The use of the synthetic antioxidant ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline, EQ) as a flame retardant in fish meal transported by sea is required by international authorities to prevent self-ignition. Because of extensive carry-over within the food chain, selective and sensitive analytical methods are required for investigations on human exposure and the safety of EQ and its metabolites. Therefore, a simple, fast, and rugged liquid-chromatography (LC) method was developed for the detection of EQ and its metabolites in fish and fishery products after liquid-liquid extraction using QuEChERS. For screening purposes, a fluorescence detector was used (LC-FLD) with the EQ-analogue methoxyquin serving as an internal standard. For stable-isotope dilution analysis by liquid chromatography-tandem mass spectrometry (SIDA-LC-MS/MS), deuterated analogues of EQ and its metabolites were synthesized for the first time and allowed for sensitive quantification and thus confirmation of screening results. Both methods were validated and successfully applied to commercially available fish samples.