Automated inline pigment removal for the analysis of pesticide residues in spinach by liquid chromatography tandem mass spectrometry

Stability Study and Handling Recommendations for Multiresidue Pesticide Mixes under Diverse Storage Conditions for LC-MS/MS and GC-MS/MS

BACKGROUND

In response to the growing global need for pesticide residue testing, laboratories must develop versatile analytical methods and workflows to produce scientifically sound results. One of the many challenges faced by food chemists is acquiring suitable pesticide certified reference materials (CRMs) to calibrate analytical equipment, monitor method performance, and confirm the identity and concentration of hundreds of pesticide residues in food samples. CRM producers invest considerable resources to ensure the stability of their products.

OBJECTIVE

To present proper CRM handling and storage practices as guidance to ensure stability based on the results of several multiresidue pesticide stability studies.

METHODS

The open ampoule and combined multiresidue mix studies were conducted under controlled conditions. New ampoules containing multiresidue pesticide CRM mixtures were opened and compared to previously opened ampoules at multiple intervals while stored under freezing and refrigerated temperatures. Both LC- and GC-amenable pesticides (>200 residues) were combined and stored under typical laboratory conditions. Studies were performed with and without celery matrix.

RESULTS

The open ampoule study showed high levels of stability for all mixtures. All GC residues remained stable over the duration of the experiment. A week after opening LC multiresidue pesticide mixtures showed minor degradation. After combination of the multiresidue pesticide mixtures, degradation occurred rapidly for both the GC and LC mixtures.

CONCLUSION

Multiresidue pesticide mixtures are stable as ampullated until they are opened. Once the contents of a kit were opened and combined, decreasing stability was observed over time. This was true for both the LC and GC kits. Working mixtures of CRMs for instrument calibration should be made daily.

HIGHLIGHTS

This article shows a novel approach for measuring stability of CRM mixes. In-depth analysis of multiresidue pesticide mixtures and the stability that can be expected before and after mixing under typical storage conditions is described.

Development and application of a mini-QuEChERS method for the determination of pesticide residues in anuran adipose tissues

The expansion of monocultures to regions close to conservation areas has put biodiversity at risk, mainly due to the intense use of pesticides. Anurans are highly susceptible to pesticides and may be a biological marker in the contamination of an area. However, methods for determining pesticides in anurans are incipient. In this work, a miniaturized QuEChERS method was developed for the extraction of atrazine, chlorpyrifos, α- and β-endosulfan, α-, β-, θ- and ζ-cypermethrin in anuran adipose tissues. The method was optimized for the tissue sample size scale according to sample mass availability. Extracting solvent and adsorbents for the clean-up step was evaluated, achieving recoveries next to 100% with acetonitrile and without a clean-up step. The mini-QuEChERS method, using 500 mg of adipose tissue, 50 mg of NaCl and 200 mg of MgSO4, 100 μL of ultrapure water, and 1.50 mL of acetonitrile with no purification step, followed by high-performance liquid chromatography analysis and photodiode array detection was validated following the European Community guidelines. The methodology showed a moderate matrix effect for some pesticides, which was corrected using the matrix-matched calibration. The limits of quantification for the pesticide residues in adipose tissues ranged from 10 to 75 μg kg-1. Pesticide recoveries ranged from 74% to 115%, and repeatability and within-lab reproducibility showed relative standard deviations < 11%. The mini-QuEChERS method was applied to extract pesticide residues from the adipose tissues of two species of anurans: Leptodactylus macrosternum and Scinax x-signatus. 25% of samples were positive, detecting endosulfan and chlorpyriphos, confirmed by liquid chromatography coupled to tandem mass spectrometry. The mini-QuEChERS was a simple, economical, and eco-friendly method for extracting pesticide residues in anuran adipose tissue samples.

Improved procedure for square-wave voltammetric sensing of fenhexamid residues on blueberries peel surface at the anodically pretreated boron-doped diamond electrode

BACKGROUND

Fungicide fenhexamid (FH) has a high residual concentration on fruits and vegetables, thus, it is of high importance to monitor the level of FH residues on foodstuff samples. So far, the assay of FH residues in selected foodstuff samples has been conducted by electroanalytical methods on sp² carbon-based electrodes that are well-known to be susceptible to severe fouling of the electrodes surfaces during electrochemical measurements. As an alternative, sp³ carbon-based electrode such as boron-doped diamond (BDD) can be used in the analysis of FH residues retained on the peel surface of foodstuff (blueberries) sample.

RESULTS

In situ anodic pretreatment of the BDDE surface was found to be the most successful strategy to remediate the passivated BDDE surface by FH oxidation (by)products, and the best validation parameters, i.e., the widest linear range (3.0-100.0 μmol L^-1), the highest sensitivity (0.0265 μA L μmol^-1) and the lowest limit of detection (0.821 μmol L^-1), were achieved on the anodically pretreated BDDE (APT-BDDE) in a Britton-Robinson buffer, pH 2.0, using square-wave voltammetry (SWV). The assay of FH residues retained on blueberries peel surface was performed on the APT-BDDE using SWV, and the obtained concentration of FH residues of 6.152 μmol L^-1 (1.859 mg kg^-1) was found to be below the maximum residue value fixed for blueberries by the European Union regulations (20 mg kg^-1).

SIGNIFICANCE AND NOVELTY

In this work, a protocol based on a very easy and fast foodstuff sample preparation procedure combined with the straightforward pretreatment approach of the BDDE surface was elaborated for the first time for the monitoring of the level of FH residues retained on the peel surface of blueberries samples. The presented reliable, cost-effective, and easy-to-use protocol could find its application as a rapid screening method for the control of food safety.

Engineering DNA G-quadruplex assembly for label-free detection of Ochratoxin A in colorimetric and fluorescent dual modes

Colorimetric and fluorescent methods for Ochratoxin A (OTA) detection are convenient and well received. However, the pigments and autofluorescence originated from food matrices often interfere with detection signals. We have developed a strategy with colorimetric and fluorescent dual modes to solve this challenge. In the colorimetric mode, OTA aptamer (AP9) was assembled into a DNA triple-helix switch with a specially designed signal-amplifying sequence. The OTA-induced G-quadruplex (G4) of AP9 would open the switch and release the signal-amplifying sequence for colorimetric signal amplification. The G4 structures of AP9 were further utilized to combine with the fluorogenic dye ThT for fluorescent mode. By skillfully engineering DNA G4 assembly for signal amplification, there was no need for any DNA amplification or nanomaterials labeling. Detections could be carried out in a wide temperature range (22-37 ℃) and finished rapidly (colorimetric mode, 60 min; fluorescent mode, 15 min). Broad linear ranges (colorimetric mode, 10-1.5 ×10³ μg/kg; fluorescent mode, 0.05-1.0 ×10³ μg/kg) were achieved. The limit of detection for colorimetric and fluorescent modes were 4 μg/kg and 0.01 μg/kg, respectively. The two modes have been successfully applied to detect OTA in samples with intrinsic pigments and autofluorescence, showing their applicability and reliability.

A cartridge-based device for automated analyses of solid matrices by online sample prep-capillary LC-MS/MS

Sample preparation is an essential step focused on eliminating interfering compounds while pre-concentrating the analytes. However, its multiple steps are laborious, time-consuming, and a source of errors. Currently, automated approaches represent a promising alternative to overcome these drawbacks. Similarly, miniaturisation has been considered an ideal strategy for creating greener analytical workflows. The combination of these concepts is currently highly desired by analytical chemists. However, most automated and miniaturised sample preparation techniques are primarily concerned with liquid samples, while solids are frequently overlooked. We present an approach based on a cartridge packed with solids (soil samples) coupled with a capillary LC-MS, combining sample preparation and analytical steps into a unique platform. As a proof-of-concept, nine pesticides used in sugarcane crops were extracted and analysed by our proposed method. For optimisation, a fractional factorial design (2^5-1) was performed with the following variables: aqueous dilution of the sample (V₁), extraction strength (V₂), matrix washing time (V₃), extraction flow (V₄), and analytical flow (V₅). After, the most influential ones (V₁, V₂, and V₃) were taken into a central composite design (2³) to select their best values. Under optimised conditions, the method reported linear ranges between 10 and 125 ng g^-1 with R² > 0.985. Accuracy and precision were in accordance with the values established by the International Council for Harmonisation (Q2(R1)). Therefore, the proposed approach was effective in extracting and analysing selected pesticides in soil samples. Also, we carried out initial qualitative tests for pesticides in honeybees to see if there is the possibility to apply our method in other solids.