Copper nanoparticle-decorated nitrogen-doped carbon nanosheets for electrochemical determination of paraquat

A new strategy to prepare copper (Cu) nanoparticles anchored in nitrogen-doped carbon nanosheets (Cu@CN) has been designed and the nanomaterial applied to the determination of paraquat (PQ). The nanocomposite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and several other techniques. We found that the Cu nanoparticles are uniformly distributed on the carbon materials, providing abundant active sites for electrochemical detection. The electrochemical behavior of the Cu@CN-based PQ sensor was investigated by square-wave voltammetry (SWV). Cu@CN exhibited excellent electrochemical activity and PQ detection performance. The Cu@CN-modified glassy carbon electrode (Cu@CN/GCE) exhibited excellent stability, favorable sensitivity, and high selectivity under optimized conditions (enrichment voltage -0.1 V and enrichment time 400 s) of the SWV test. The detection range reached 0.50 nM to 12.00 μM, and the limit of detection was 0.43 nM with high sensitivity of 18 μA·μM^-1·cm^-2. The detection limit is 9 times better than that of the high-performance liquid chromatography method. The Cu@CN electrochemical sensor demonstrated excellent sensitivity and selectivity also in environmental water and fruit samples enabling its use in practical, rapid trace-level detection of PQ in environmental samples.

Determination of Highly Polar and Ionic Pesticides in Grape and Pomegranate Using Liquid Chromatography Tandem Mass Spectrometry

Background

Residues of polar pesticides cannot be determined by QuEChERS-based multiresidue extractions because of their non-amenability to reverse-phase chromatographic separation and poor recoveries. On the other hand, single-residue methods pose limitations because of the various requirements of sample preparation and LC-MS/MS conditions. A new multiresidue method is thus warranted for rapid and simultaneous analysis of polar pesticides.

Objective

The study developed a multiresidue method for the simultaneous analysis of glyphosate and its metabolite (aminomethylphosphonic acid, AMPA), glufosinate and its metabolites (3-methylphosphinicopropionic acid and N-acetyl-glufosinate), ethephon, fosetyl-aluminum and its metabolite (phosphonic acid), and trimesium in grape and pomegranate by LC-MS/MS.

Method

The homogenized samples (10 g) were extracted with acidified methanol (20 mL). An aliquot of the extract was diluted with acetonitrile (1 + 1) and measured by LC-MS/MS using a Torus DEA column. The performance of a hydrophilic interaction liquid chromatography (HILIC) column and an “anionic polar pesticides” (APP) column was also evaluated.

Results

The method performance on the Torus DEA column was satisfactory for all compounds (recoveries = 77–104%, repeatability-RSD, <11%) at limit of quantification (LOQ) (0.01 mg/kg), and with higher levels in grape and pomegranate. The only exception was AMPA, which had an LOQ of 0.05 mg/kg. In the APP column, AMPA could be determined with an LOQ of 0.01 mg/kg. Trimesium, which had poor retention in Torus DEA, performed better in an XBridge HILIC column (retention time = 4.2 min, LOQ = 0.01 mg/kg). The inter-laboratory validation experiment yielded comparable results with high accuracy and precision.

Conclusions

The method could screen the residues of all compounds on a Torus DEA column. For AMPA and trimesium, the APP and XBridge HILIC columns provided superior method performances. Since isotopically labeled internal standards were not required, the method appeared cost-effective. Considering its compliance with the SANTE/12682/2019 validation guidelines and EU-MRLs, the method can be recommended for regulatory testing purposes.

Highlights

A high-throughput residue analysis method targeting nine polar and ionic compounds in grape and pomegranate involved a single multiresidue extraction, followed by direct analysis using LC-MS/MS. A satisfactory method performance was achieved through intra- and inter-laboratory validation. The method sensitivity met the EU-MRLs and the SANTE/12682/2019 analytical quality control criteria.

Critical Evaluation of Analytical Methods for the Determination of Anthropogenic Organic Contaminants in Edible Oils: An Overview of the Last Five Years

Anthropogenic contaminants, as pesticides, polycyclic aromatic hydrocarbons (PAHs) and monochloropropanediols (MCPDs), have become important to be controlled in edible oils, since their regular occurrence. In fact, alerts from the Rapid Alert System for Food and Feed (RASFF) in oils normally include these compounds. From a critical point of view, tools used to control these compounds in the last 5 years will be discussed, including sample preparation, analysis and current regulations. Extraction and analysis methods will be discussed next, being liquid-liquid extraction (LLE) and QuEChERS, with or without clean-up step, as well as chromatographic methods coupled to different analyzers (mainly mass spectrometry), the most commonly used for extraction and analysis respectively. Occurrence in samples will also be reviewed and compared with the legal maximum residue limits (MRLs), observing that 4%, 20% and 60% of the analyzed samples exceed the legal limits for pesticides, MCPDs and PAHs respectively.

Monitoring of Paraquat in soya products intended for animal feed

Even though paraquat is considered to be one of the most toxic herbicides, it is one of the most used ones. Paraquat-based preparations are heavily used across many important agricultural countries and for a lot of types of crops such as soya. As soya is used in large quantities in the feed production, paraquat residues in soya products are a potential threat to livestock. The aim of this study was to investigate whether soya products intended for animal feed contain residues of paraquat. Therefore, an optimized Quick Polar Pesticides (QuPPe) Method was developed. In total, 174 samples were analyzed via LC-MS/MS using zwitterionic hydrophilic interaction liquid chromatography (ZIC-HILIC). The results showed that paraquat was detected in 66 % of the samples above 0.008 mg/kg. Residues were mainly present in soya bean meals that were imported from Brazil or the USA and cultivated using genetically modified soya. Around 5 % of the samples were not compliant with the European regulation on maximum residue levels of pesticides in or on food and feed. The results of this study support the view that paraquat residues play a significant role in soya products intended for animal feed and, thus, need to be controlled on a regular basis. However, for enforcement actions reliable processing factors for paraquat in soya products or maximum residue levels for processed soya products are urgently required.

Permanently Positively Charged Stable Isotope Labeling Agents and Its Application in the Accurate Quantitation of Alkylphenols Migrated from Plastics to Edible Oils

A new permanently positively charged stable isotope labeling (SIL) agent pair, 4-(((2,5-dioxopyrrolidin-1-yl)oxy)carbonyl)-N,N,N-trimethylbenzenaminium iodide(DPTBA) and its deuterated counterpart d₃-DPTBA, was designed and synthesized. The SIL agents were applied to the liquid chromatography-tandem mass spectrometry analysis of alkylphenols. Light labeled standards and heavy labeled samples were mixed and analyzed simultaneously. Matrix effect which mainly occurred during the ionization process was minimized because of the identical ionization processes between samples and standards. Meanwhile, derivatization made alkylphenols be positively charged, and thus the sensitivity was enhanced. The limits of detection were in the range of 1.5-1.8 ng/L, and the limits of quantitation were in the range of 4.8-6.1 ng/L. The developed method was applied to analyze alkylphenols migrated from plastics to edible oils. The recoveries for all analytes were in the range of 88.6-95.3%, while the matrix effects for all analytes were in the range of 96.2-99.6%.