Optimization and Validation of a Multiresidue Pesticide Method in Rice and Wheat Flour by Modified QuEChERS and GC–MS/MS

Simultaneous Analysis of 53 Pesticides in Safflower (Carthamus tinctorius L.) by Using LC-MS/MS Coupled with a Modified QuEChERS Technique

OBJECTIVE

An optimized quick, easy, cheap, effective, rugged, and safe (QuEChERS) technique was investigated and compared with the conventional QuEChERS technique for the simultaneous analysis of fifty-three pesticide residues in safflower using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS).

METHOD

Graphitic carbon nitride (g-C₃N₄) consisting of a major amount of carbon and nitrogen with a large surface area was used as a QuEChERS adsorbent instead of graphitized carbon black (GCB) for safflower extraction purification. Validation experiments were performed using spiked pesticide samples, and real samples were analyzed.

RESULTS

The linearity of the modified QuEChERS technique was evaluated with high coefficients of determination (R-2) being higher than 0.99. The limits of detection were <10 μg/kg. The spiked recoveries ranged from 70.4% to 97.6% with a relative standard deviation of less than 10.0%. The fifty-three pesticides exhibited negligible matrix effects (<20%). Thiamethoxam, acetamiprid, metolachlor, and difenoconazole were detected in real samples using an established method.

CONCLUSION

This work provides a new g-C₃N₄-based modified QuEChERS technique for multi-pesticide residue analysis in complex food matrices.

Pesticide residues analysis in passion fruit and its processed products by LC-MS/MS and GC-MS/MS: Method validation, processing factors and dietary risk assessment

A method for the determination of 80 pesticides (including five metabolites) in passion fruit using ethyl acetate extraction and dispersive solid-phase extraction followed by LC-MS/MS and GC-MS/MS was validated at LOQ of 0.005 or 0.010 mg kg^-1 (70 to 120% recovery; RSD ≤ 20%). Fifty-five passion fruit samples were obtained from producers, and 30 samples of frozen pulp and 12 samples of flour purchased. About 27% of the pesticides were detected; at least one in 60% of the peel samples, mainly imidacloprid and carbendazim (max. of 0.274 mg kg^-1). Median processing factor was 0.5 for washed peel and 6.5 for dried peel (flour). About 63% of frozen pulp samples were positive, and 4 flour samples contained residues, mainly methamidophos. About 70% of the detected pesticides are not authorized in passion fruit in Brazil. Chronic and acute exposure from the consumption of passion fruit products did not indicate a health concern.

High resolution mass spectrometry workflow for the analysis of food contaminants: Application to plant toxins, mycotoxins and phytoestrogens in plant-based ingredients

An analytical workflow including mass spectral library, generic sample preparation, chromatographic separation, and analysis by high-resolution mass spectrometry (HRMS) was developed to gain insight into the occurrence of plant toxins, mycotoxins and phytoestrogens in plant-based food. This workflow was applied to 156 compounds including 90 plant toxins (pyrrolizidine alkaloids, tropane alkaloids, glycoalkaloids, isoquinoline alkaloids and aristolochic acids), 54 mycotoxins (including ergot alkaloids and Alternaria toxins) and 12 phytoestrogens (including isoflavones, lignans and coumestan) in plant-based protein ingredients, cereal and pseudo-cereal products. A mass spectral library was built based on fragmentation spectra collected at 10 different collision energies in both positive and negative ionisation modes for each toxin. Emphasis was put on a generic QuEChERS-like sample preparation followed by ultra-high-pressure liquid chromatography using alkaline mobile phase allowing the separation of more than 50 toxic pyrrolizidine alkaloids. HRMS acquisition comprised a full-scan event for toxins detection followed by data-dependent MS2 for toxin identification against mass spectrum. Method performance was evaluated using fortified samples in terms of sensitivity, repeatability, reproducibility and recovery. All toxins were positively identified at levels ranging from 1 µg kg-1 to 100 µg kg-1. Quantitative results obtained by a standard addition approach met SANTE/12682/2019 criteria for 132 out of 156 toxins. Such a workflow using generic, sensitive and selective multi-residue method allows a better insight into the occurrence of regulated and non-regulated toxins in plant-based foods and to conduct safety evaluation and risk assessments when needed.

Residue Analysis of Insecticides in Potatoes by QuEChERS-dSPE/UHPLC-PDA

Insecticides are broadly applied in agriculture to defend crops from illnesses and pest attacks, consequently guaranteeing high production. However, their residual deposits in food products are becoming a main concern with regard to human consumption. As such, sensitive analytical methods should be developed to assess, prevent and control insecticide residues. In this research, an accurate, fast and reliable residual analytical method, that is quick, easy, cheap, effective, rugged and safe, combined with dispersive solid phase extraction (QuEChERS-dSPE), was developed for the determination of the most common insecticides used in potatoes cultivation (chlorpyrifos, λ-cyhalothrin, deltamethrin and acrinathrin), using an ultra-high performance chromatography photodiode array detector (UHPLC-PDA). The most influential extraction and instrumentation parameters that affect the method’s performance, such as extraction solvent, ratio salts, sorbents, stationary phases, gradient conditions and eluents, were assessed. Under the ideal conditions, good linearity (0.992–0.998), limits of detection (0.02–0.47 µg/kg) and quantification (0.06–1.58 µg/kg), recovery (94.1 to 112%) and precision (relative standard deviation <18%) were achieved for spiked levels between 2.5 and 50 µg/kg. The obtained results revealed that the potatoes analyzed do not represent any concern for human healthy, as the insecticide residues detected were lower than the maximum residue limits set by the European Union, Codex Alimentarius, and other organizations.

Modified QuEChERS Extraction and HPLC-MS/MS for Simultaneous Determination of 155 Pesticide Residues in Rice (Oryza sativa L.)

Rice (Oryza sativa L.) is the staple food of more than half of the world’s population. The main factors affecting the quality of rice include grain length, texture, stickiness, flavor, and aroma. Pesticides are intended for the protection of plant products from weeds, fungi, or insects. However, pesticides also result in negative effects such as environment disturbances, pest resistance and toxicity to both users and food consumers. The aim of this study was to conduct validation experiments of a method for the determination of multi-pesticides in rice, a model food of other cereals. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was used for the extraction of pesticide residues from rice followed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) with a triple quadrupole instrument using electrospray ionization. The analytical method has chromatography-tandem according to SANTE/11813/2017. The limit of quantification was 5 μg/kg. Recoveries for the 155 analyzed pesticides ranged between 77.1% for pirimiphos-ethyl and 111.5% for flutriafol and they were determined at 3 spiking levels. The proposed method was demonstrated to be quick, simple, precise, and accurate and allowed for evaluating the compliance of cereals samples with legislated maximum residue levels of pesticides in the European Union.

Residual behavior and risk assessment of butralin in peanut fields

Butralin is widely used to control single-leaf weeds and some dicotyledons. The application of butralin in the environment may cause residue beyond regulation criteria and residual toxicity. Therefore, it is important to detect and supervise the dissipation behavior of butralin in edible raw food and in the environment. The aim of this study was to monitor butralin in peanuts and soil under farmland conditions and examine the likely dietary risk assessment of butralin for Chinese people on the basis of residual concentrations. A method for the analysis of butralin residue and its dissipation in peanut plants and soil under field conditions was investigated. The results show that an analytical method for the quantization of butralin in peanuts and soil utilizing gas chromatography with electron capture detection (GC-ECD) was developed. Standard recovery experiments using three different butralin spiking levels of 0.01, 0.1, and 1.0 mg kg^-1 in different samples (i.e., peanut kernels, shell, seedling, stalk, and soil) were conducted. The recoveries of butralin from all matrices ranged from 86 to 108% with relative standard deviations from 3 to 6% (n = 5). The limit of quantification (LOQ) of the method was 0.01 mg kg^-1. After storage at - 20 °C for 365 days, the degradation rate of residues of butralin in peanut kernels was less than 30%, which met the storage stability test criteria for pesticide residues in stored commodities of plant origin. The dissipation half-lives of butralin ranged from 4.2 to 6.6 days and 4.6 to 6.6 days in peanut seedlings and soil, respectively, in farmland ecosystems. At the normal harvest time, the final residue concentrations of butralin in peanuts and soil were all below the LOQ. The final total risk quotient (RQ) values were much lower than RQ = 100%, which indicated that the long-run fitness risk associated with butralin residue in different groups of registered crops is correspondingly low for people in China. The current research results could offer guidance for the rational use of butralin and provide data support for the building of maximum residue limits (MRLs) in China.

One-step synthesized magnetic MIL-101(Cr) for effective extraction of triazine herbicides from rice prior to determination by liquid chromatography-tandem mass spectrometry

The magnetic metal-organic framework MIL-101(Cr) material-based solid-phase extraction method coupled with high-performance liquid chromatography and tandem mass spectrometry was applied to extract seven triazine herbicides in rices. Fe₃ O₄ /MIL-101(Cr) was synthesized using reduction-precipitation method, in which steps including pre-synthesis and modification of Fe₃ O₄ nanoparticles were by-passed. Various parameters including extraction solvent type and volume, ultrasonic extraction time, amount of Fe₃ O₄ /MIL-101(Cr) microspheres, adsorption time, desorption volume and time were investigated. Under optimal conditions, the proposed method had the limit of detection (S/N = 3) and the limit of quantification (S/N = 10) of 1.08-18.10 and 3.60-60.20 pg/g, respectively. Relative standard deviations calculated for all herbicides with concentrations of 2 and 20 ng/g were in the range of 0.5 to 13% (n = 3). In addition, at the two above-mentioned concentrations, the method achieved relative recoveries percentages of 79.3 to 116.7% when applied to determine the triazine herbicides in real samples spiked. This rapid, green, non-polluting, pre-concentrated extraction method was successfully developed and applied to analyze herbicides in rice samples.

Determining pesticide residues in wheat flour by ultrahigh-performance liquid chromatography/quadrupole time-of-flight mass spectrometry with QuEChERS extraction

Pesticides are used to increase crop yields and preserve quality by protecting crops against pests; however, their overuse can adversely affect human health and the environment. Herein, we report the development of a multi-pesticide screening method using optimized QuEChERS coupled with liquid chromatography/quadrupole time-of-flight (QTOF) mass spectrometry for the analysis of 13 pesticides in wheat flour. Mass accuracies with errors of less than 2.4 ppm were obtained for all analysed pesticides, and the method provided satisfactory recovery and linearity. Repeatabilities of 0.3-12.7% and reproducibilities of 2.5-15.2% were observed in full-scan TOF mode. The performance of the developed full-scan TOF method was compared to that obtained in high-resolution multiple reaction monitoring (MRM-HR) mode. The limits of quantification for the full-scan TOF and MRM-HR modes ranged from 2 to 10, and 3 to 9 μg kg^-1, respectively. The two quantification methods exhibited high sensitivities (limit of detections: 1-3 μg kg^-1 in full-scan TOF, and 1-3 μg kg^-1 for MRM-HR mode). No pesticide residues were detected when the developed method was applied to 22 real wheat flour samples.

A liquid chromatography with tandem mass spectrometry method to simultaneously determinate chlorpyrifos, imidacloprid and imidacloprid metabolites in wheat

A liquid chromatography with tandem mass spectrometry method was developed and validated to simultaneously determine chlorpyrifos, imidacloprid, and imidacloprid metabolites in soil, wheat grain, and wheat straw matrices. Satisfactory linearity (R² ≥ 0.9965) of the method was obtained for all analytes. The ranges of limits of detection and limits of quantification for seven analytes in three matrices were 0.17-66.7 and 0.5-200 μg/kg, respectively. Average recoveries were 72.85-81.25% for chlorpyrifos, 78.54-84.70% for imidacloprid, 73.83-81.03% for imidacloprid olefin, 71.47-80.61% for 5-hydroxy imidacloprid, 71.79-81.32% for imidacloprid urea, 70.42-82.20% for imidacloprid nitroguanidine, and 70.91-82.46% for imidacloprid 6-chloronicotinic acid in soil, wheat grain, and wheat straw. The intra- and interday relative standard deviations were less than 8%. The established method was successfully applied for the residual analysis of chlorpyrifos, imidacloprid, and imidacloprid metabolites in actual soil, wheat grain, and wheat straw samples. The results indicated that the established method could be used to detect trace amounts of chlorpyrifos, imidacloprid, and imidacloprid metabolites in wheat and that the method might be able to provide some data on the detection of these seven compounds in other crops.

Novel sequential separation and determination of a quaternary mixture of fungicides by using an automatic fluorimetric optosensor

A versatile flow-through multi-optosensor is proposed for the separation and spectrofluorimetric determination of mixtures of four widely used pesticides: carbendazim, thiabendazole, carbaryl and o-phenylphenol at µg g^-1 levels in fruits. The flow system is based on the online pre-concentration and separation of the pesticides on a solid sensing microzone, followed by the sequential measurement of their native fluorescence. The separation of the pesticides takes place on a solid support located in the same flow cell, on which analytes are temporarily immobilized and separated from the matrix due to their different retention/desorption kinetics when they interact with the C₁₈ silica gel microbeads. Suitable analytical parameters were obtained for the selected analytes, with method detection and quantification limits ranging between 0.1-0.5 and 0.2-1.6 µg g^-1, respectively. These values comply with the maximum residue limits (MRLs) established by the Codex Alimentarius for these commodities; in addition, carbendazim, thiabendazole and ortho-phenylphenol comply with the MRLs of The European Union. The developed method was applied to the analysis of citrus fruits by performing recovery studies. Recoveries between 85% and 115% were obtained in all cases, and the results were confirmed by a liquid chromatography-mass spectrometry reference method.

Deposition amount and dissipation kinetics of difenoconazole and propiconazole applied on banana with two commercial spray adjuvants

A rapid and sensitive method for the simultaneous determination of difenoconazole and propiconazole residues in banana matrices was established using GC-MS/MS. The average recovery rates of difenoconazole and propiconazole from various matrices ranged from 76.7% to 94.9%. The relative standard deviation was between 0.9% and 7.4%. The effect of adding organosilicon and mineral oil adjuvants after being applied to the residues of difenoconazole and propiconazole in banana leaves was examined. The initial deposition amount 2 hours after the adjuvant treatment with organosilicon and mineral oil was 1.22–2.13 times higher than that after water treatment. After adding the two spray adjuvants, the residues of the two pesticides at 2 hours on three samples followed the order leaves > soil > fruit. The degradation half-lives of the two pesticides were in the range of 1.91–7.30 days for all the three treatments in two typical banana-growing areas in China. The degradation half-lives of the two pesticides in the water treatment group and the mineral oil treatment group were similar. However, organosilicon could apparently increase the half-life of difenoconazole on banana leaves. The final levels of difenoconazole and propiconazole residues on whole banana fruits were ≤0.1 mg kg⁻¹ (MRL) 14 days after application. The results of this work may aid the safe use of difenoconazole and propiconazole in banana production, especially when used with organosilicon and mineral oil adjuvants.

The effect of adding organosilicon and mineral oil adjuvants after being applied to the residues of difenoconazole and propiconazole in banana leaves was studied. The partition of the pesticides between soil, leaves and fruits was evaluated.

Validation of a QuEChERS-Based Gas Chromatography-Mass Spectrometry (GC-MS) Method for Analysis of Phthalate Esters in Grain Sorghum

A modified QuEChERS method coupled with gas chromatography-mass spectrometry (GC-MS) was developed for analysis of 14 phthalate esters (PAEs) in grain sorghum (GS). Chemical extraction was done with acetonitrile followed by dispersive-solid phase extraction technique with a mixture of sorbents including primary secondary amine and octadecyl silica. Under the optimized condition, the matrix-matched calibration curves for all PAEs showed good linear relationship in the concentration range between 5 and 500 μg/L with correlation coefficients (R² ) better than 0.99. Mean recoveries were between 82.0% and 120.2% at spiking levels of 0.06, 0.6, and 2.0 mg/kg with RSD of 0.3% to 7.8% (n = 5) for intra-day precision and 1.2% to 7.6% (n = 5) for inter-day precision. The LOD_GS and LOQ_GS for 14 PAEs were between 0.4 and 10.0 μg/kg and 0.5 and 20.0 μg/kg, respectively. Analysis of 32 commercial GS samples revealed that dimethyl-, diethyl-, diisobutyl-, dibutyl-, and di- (2-ethylhexyl) phthalate esters were detected in all of the analytes. In addition, content-color scale model was applied to visualize the concentration differences of PAEs in real GS samples. Principal component analysis of PAEs revealed that the GS samples did not have a distinctive cluster based on their geographic origins. The established method was proven to be simple, accurate, and effective for analysis of PAEs in GS, which might also be applied for analysis of PAEs in other matrices.

PRACTICAL APPLICATION

A modified QuEChERS-based GC-MS method was developed for the determination of phthalate esters (PAEs) in grain sorghum (GS). The ubiquitous presence of PAEs can migrate into GS. Therefore, evaluation of the total content of PAEs in GS is helpful to understand its impact of overall pollution level on other foods. This study has provided some basic information in terms of the content and contamination of PAEs in GS, which is helpful to establish relevant standards and risk assessment of GS for the government.

Rapid and Simultaneous Analysis of 360 Pesticides in Brown Rice, Spinach, Orange, and Potato Using Microbore GC-MS/MS

A multiresidue method for the simultaneous and rapid analysis of 360 pesticides in representative agricultural produce (brown rice, orange, spinach, and potato) was developed using a modified QuEChERS procedure combined with gas chromatography-tandem mass spectrometry (GC-MS/MS). Selected reaction monitoring transition parameters (e.g., collision energy, precursor and product ions) in MS/MS were optimized to achieve the best selectivity and sensitivity for a wide range of GC-amenable pesticides. A short (20 m) microbore (0.18 mm i.d.) column resulted in better signal-to-noise ratio with reduced analysis time than a conventional narrowbore column (30 m × 0.25 mm i.d.). The priming injection dramatically increased peak areas by masking effect on a new GC liner. The limit of quantitation was <0.01 mg/kg, and the correlation coefficients (r²) of matrix-matched standards were >0.99 within the range of 0.0025-0.1 mg/kg. Acetonitrile with 0.1% formic acid without additional buffer salts was used for pesticide extraction, whereas only primary-secondary amine (PSA) was used for dispersive solid phase extraction (dSPE) cleanup, to achieve good recoveries for most of the target analytes. The recoveries ranged from 70 to 120% with relative standard deviations of ≤20% at 0.01 and 0.05 mg/kg spiking levels (n = 6) in all samples, indicating acceptable accuracy and precision of the method. Seventeen real samples from local markets were analyzed by using the optimized method, and 14 pesticides in 11 incurred samples were found at below the maximum residue limits.

Evaluation of alternative sorbents for dispersive solid-phase extraction clean-up in the QuEChERS method for the determination of pesticide residues in rice by liquid chromatography with tandem mass spectrometry

Many compounds are used for pest control during the production and storage of rice, making it necessary to employ multiclass methods for pesticide residues determination. For this purpose, QuEChERS-based methods are very efficient, fast and accurate, and improvements in the clean-up step are important, especially for complex matrices, like cereals. In this work, different sorbents such as chitosan, florisil(®) , alumina, diatomaceous earth, graphitized carbon black, besides the commonly used primary secondary amine and octadecylsilane, were evaluated for dispersive solid-phase extraction clean-up in acetate-buffered QuEChERS method for the determination of residues of 20 representative pesticides and one metabolite in rice by liquid chromatography coupled to tandem mass spectrometry. The sorbent C18 presented the best results, however, chitosan showed similar results, and the best performance among the unconventional sorbents evaluated. The method limit of quantification, attending accuracy (70-120% recovery) and precision (RSD ≤20%) criteria, ranged from 5 to 20 μg/kg. Results showed that chitosan is an effective alternative to reduce analysis costs, maintaining the method reliability and accuracy.