Application of Fast Gas Chromatography–Mass Spectrometry in Combination with the QuEChERS Method for the Determination of Pesticide Residues in Fruits and Vegetables

A fast gas chromatography–mass spectrometry method has been developed for multiresidue determination of up to 56 pesticides in fruits and vegetables in a chromatographic run time of <10 min, using a single quadrupole mass spectrometer operating in selected ion monitoring mode. The well-known acetate-buffering version of the QuEChERS method has been used for sample preparation. Programmable temperature vaporizer injection of 3 μL allowed reaching limits of detection between 0.15 and 15 μg/kg for most compounds in the sample matrices tested. The applicability of the method has been evaluated in apple, orange, carrot, and tomato. Recoveries at three fortification levels (0.01, 0.1 and 0.5 mg/kg) ranged from 70 to 120 % for most compounds, with relative standard deviations below 20 % in all cases. The developed method has been applied to fruit and vegetable samples from different Spanish provinces.     

Determination of Amoxicillin Stability in Chicken Meat by Liquid Chromatography–Tandem Mass Spectrometry

An amoxicillin stability study was performed under different pH (1, 3 and 5) and temperature (4 °C, 22 °C, 37 °C and 55 °C) conditions and for incurred samples stored at −20 °C with the goals of better understanding amoxicillin degradation and characterising its main degradation products (amoxicilloic acid and amoxicillin diketopiperazine). The analytical methodology used consisted of a simple extraction using phosphate buffer (pH 8) with sodium chloride followed by a sample clean-up using OASIS? HLB cartridges and a liquid chromatography–tandem mass spectrometric analysis. Amoxicillin was found to be greatly unstable at temperatures above 22 °C for all pH values studied, so it was recommended that biological samples should be frozen at temperatures below −70 °C until analysis of the amoxicillin residues.     

Modified QuEChERS Combination with Magnetic Solid-Phase Extraction for the Determination of 16 Preservatives by Gas Chromatography–Mass Spectrometry

In this paper, based on the mechanism of the quick, easy, cheap, effective, rugged and safe (QuEChERS) method, a novel graphene grafted silica-coated Fe₃O₄ (Fe₃O₄@SiO₂@G) was synthesized and applied as the efficient magnetic solid-phase extraction (MSPE) adsorbent for rapid cleanup of vegetable samples prior to analyzing 16 preservative residues by gas chromatography–mass spectrometry (GC-MS). The method, which took advantages of the novel nanoparticle adsorbent and an external magnetic field separation targets from samples, not only could avoid the time consuming of the traditional solid-phase extraction, but also could be developed for simultaneous determination of 16 preservative residues in vegetables. Various experimental parameters that could affect the extraction efficiencies have been investigated. Under the optimum conditions, 16 preservatives showed good linearity over the range of 0.02–2.00 mg/L and correlation coefficients (R ²) of 0.9946–0.9998. The limits of detections (LODs) were in the range of 0.21–11.50 μg/kg. The recoveries of 16 preservatives ranged from 78.3 to 116.7 %, and the relative standard deviations (RSDs) ranged from 1.4 to 11.9 %.     

A Rapid Determination of Ergosterol in Grains Using Gas Chromatography–Mass Spectrometry Method Without Derivatization

Food Analytical Methods - A simple, rapid and sensitive GC-MS method using on-column injection was developed and validated to determine ergosterol (ERG) levels in maize and wheat. In this method,...     

Simultaneous Determination of 69 Pesticide Residues in Coffee by Gas Chromatography?CMass Spectrometry

A method using gel permeation chromatography (GPC) combined with solid-phase extraction (SPE) cleanup followed by gas chromatography–mass spectrometry (GC-MS) has been established for quantitative determination of 69 pesticide residues in coffee. Based on an appraisal of the characteristics of GC-MS, validation experiments were conducted for 69 pesticides. In the method, 2.0 g samples were mixed with 5 ml water and 1 g sodium chloride and extracted with 5 ml of ethyl acetate by blender homogenization, centrifugation, and filtration. Evaporation was conducted and the sample was injected into a 250 mm × 10 mm S-X3 GPC column, with ethyl acetate–n-hexane (1:2 v/v) as the mobile phase at a flow rate of 3 ml/min. The 4–15 min fraction was collected for the SPE cleanup, which was Envi-Carb SPE cartridge coupled with NH₂-LC SPE cartridge with acetone–ethyl acetate (2:5 v/v) as the eluted solvent. The eluents were collected and then evaporated to dryness, which was redissolved in 0.5 ml ethyl acetate for GC-MS analysis. For the 69 pesticides determined by GC-MS, the portions collected from GPC were concentrated to 0.5 ml and exchanged with 5 ml n-hexane. In the linear range of each pesticide, the correlation coefficient was R ² ≥ 0.99. At the low, medium, and high fortification levels of 0.05–1.0 mg/kg, recoveries fell within 60–120%. The relative standard deviation was between 1.3% and 22.3% for all 69 pesticides. The limits of detection for the method were 10 μg/kg to 150 μg/kg, depending on each pesticide.     

Direct Chiral Determination of Acephate and Its Metabolite Methamidophos in Vegetables Using QuEChERS by Gas Chromatography–Tandem Mass Spectrometry

Currently, methamidophos, the main metabolite of acephate in the plants, has been paid particular attention in the risk evaluation of acephate because of its severely accurate toxicity, but the chirality of methamidophos and acephate has not been taken into account. In this study, a chiral separation and analysis method was developed to help evaluate the risks posing to the environment and human health. The efficiency of four commercial chiral capillary columns to accomplish enantioseparation of these two pesticides was firstly evaluated, and the chromatographic condition on the chose column BGB-176 SE was optimized. An analytical method for determination and confirmation of the enantiomers in vegetables by gas chromatography–tandem mass spectrometry was then developed with the column. QuEChERS was adopted to extract and clean the residues in vegetables. The mean recovery rates of quintuplicate results in cabbage and pakchoi ranged from 71.87 to 81.45 %; the relative standard deviation was less than 8.81 %. The limits of detection of enantiomers of acephate and methamidophos were 0.008 and 0.005 mg/kg, respectively. After the application of the method to vegetables from a market, it was proved that the metabolism of acephate and methamidophos in plants should be enantioselective.     

Simple Method for Determination of Fungicides in Citrus Fruits by Liquid Chromatography–Tandem Mass Spectrometry

A simple method for the determination of four fungicides (thiabendazole, imazalil, o-phenylphenol, and diphenyl) in citrus fruits has been developed. After spiking surrogates of these fungicides, the sample was extracted with acetonitrile, salted out, and the water was simultaneously removed using anhydrous magnesium sulfate and sodium chloride. The extract was first purified with a primary secondary amine and octadecylsilane, followed by the addition of dimethyl sulfoxide as a keeper solvent, and subsequently concentrated under a nitrogen stream. The compounds were analyzed by liquid chromatography–tandem mass spectrometry using the atmospheric pressure photoionization interface. The recoveries and relative standard deviations (RSDs) of the fungicides (1 mg kg^?1) were satisfactory (recovery 92–114 %; RSD <10 %). An evaluation with Shewhart QC plots revealed that all data points are within the controlled area, thus confirming the robustness of the method for analyzing the fungicide content of citrus fruits. The sample preparation time for ten samples was approximately 2 h, highlighting the time and labor efficiency of the method.     

Determination of Botanical Insecticides Residues in Fish by Liquid Chromatography�CElectrospray Tandem Mass Spectrometry

A method for determining residues of four botanical insecticides oxymatrine, matrine, rotenone, and azadirachtin in fish by liquid chromatography–electrospray tandem mass spectrometry (LC–MS/MS) is described. The extraction was achieved using acetonitrile, with the addition of sodium chloride to induce a salting out effect before using n-hexane to defat. Chromatographic separation is achieved on Phenomenex Luna C18 column in the mobile phase composition of acetonitrile and 5 mmol/L ammonium acetate buffer consisting formic acid to provide protons for LC–MS/MS analysis. Accomplishing with the matrix matched calibration curves to compensate for the matrix effect, the quantitative data showed good linear response within the concentration ranges studied. Detection is carried out using positive-ion electrospray tandem mass spectrometry. Calibrations were linear over a working range of 0.5–50 μg/L for oxymatrine, matrine, rotenone, and 2–200 μg/L for azadirachtin. The average recoveries and the relative standard deviation ranged from 88.6–95.7% and 7.58–10.2%, respectively, in spiked fish samples at concentration levels ranging from 0.5 to 10 μg/kg for oxymatrine, matrine, and rotenone and from 2 to 50 μg/kg for azadirachtin. The limits of detection for oxymatrine, matrine, rotenone, and azadirachtin were 0.29, 0.37, 0.21, and 1.4 μg/kg, respectively. The method is accurate, specific, and sensitive for the analysis of the studied botanical insecticides residues in fish samples.     

Determination of Six Paraben Residues in Fresh-cut Vegetables Using QuEChERS with Multi-walled Carbon Nanotubes and High-Performance Liquid Chromatography–Tandem Mass Spectrometry

In this study, an optimized QuEChERS sample preparation method was developed to analyze residues of six parabens: methyl-, ethyl-, n-propyl-, isopropyl-, n-butyl-, and isobutylparaben in five fresh-cut vegetables (potato, broccoli, carrot, celery, and cabbage) with high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS). Homogenized samples were extracted using acetonitrile, and the extracts were cleaned with the novel sorbent multi-walled carbon nanotubes (MWCNTs). MWCNTs provided 84–94% removal of chlorophyll and lower matrix effects (MEs) compared to commonly used primary-secondary-amine (PSA) sorbent. Selected parabens were separated by HPLC with isocratic elution using acetonitrile and 0.1% (v/v) formic acid solution and determined by triple quadrupole MS/MS. The method validation results showed that recoveries were at 70–120% with RSDs <20%. Calibration curves showed linear responses of six parabens with R ² > 0.99. Fifty fresh-cut vegetable samples from different farmer markets in Beijing, China were collected to measure the paraben residues, and only one sample was tested positive with methylparaben concentration at 81 μg/kg.     

Determination of Chlorothalonil Residue in Cabbage by a Modified QuEChERS-Based Extraction and Gas Chromatography–Mass Spectrometry

Being susceptible to any matrix with pH >5, taking cabbage as an example, the low recovery of chlorothalonil residues adsorbed onto the cabbage matrix was almost completely improved by extracting with 1/1 (v/v) acetonitrile (containing 5 % acetic acid)/toluene. Under the optimized conditions, the recoveries of chlorothalonil in cabbage fortified at three concentrations of 0.5 to 10 mg kg^?1 were 71–93 % with relative standard deviations (RSDs) lower than 6 %. The limit of detection (LOD) and the limit of quantification (LOQ) of the gas chromatography–mass spectrometry (GC–MS) method for chlorothalonil were 0.05 and 0.5 mg kg^?1, respectively, which were much lower than the maximum residue limits (MRLs). The proposed analytical method demonstrated a potential for its application to monitor for chlorothalonil and to help assure food safety, especially base-sensitive-pesticide analysis.     

Comparison of Simple and Rapid Extraction Procedures for the Determination of Pesticide Residues in Fruit Juices by Fast Gas Chromatography–Mass Spectrometry

Three sample treatment methods, based on QuEChERS, solid-phase extraction (SPE) and solid-phase microextraction (SPME), were compared and evaluated in order to obtain the best conditions to determine pesticide residues in fruit juice by fast gas chromatography–mass spectrometry (single quadrupole GC-MS). Analysis were performed under selected ion monitoring, acquiring the three most abundant and/or specific ions for each analyte and using their relative intensity ratios as a confirmatory parameter. The 3 methodologies (QuEChERS, SPE and SPME) were validated taking 15 selected pesticides as model compounds, using commercial apple juice. QuEChERS procedure was based on the AOAC Official Method 2007.01, using acetonitrile (containing 1 % acetic acid) as extraction solvent and primary–secondary amine during the dispersive solid-phase extraction. Oasis hydrophilic–lipophilic balance cartridges were used for SPE, and polyacrylate fibers were used for direct immersion SPME procedure. Three isotopically labeled standards were added to the samples before extraction and used as surrogate standards. Validation parameters as recoveries, limits of detection, and limits of quantification (LOQ), as well as matrix effects and sample throughput, were obtained and compared for the three extraction procedures. QuEChERS was considered faster and led to the best quantitative results. In this way, validation was extended to up to 56 pesticides by applying QuEChERS in multi-fruit juice samples, obtaining LOQs ranging from 2 to 20 μg/L for most compounds. Accuracy and precision were evaluated by means of recovery experiments at two concentration levels (10 and 100 μg/L), obtaining recoveries between 70 and 120 % in most cases and relative standard deviations below 15 %. Finally, the QuEChERS method was applied to the analysis of commercial juices, including mango–apple, pineapple, grapefruit and orange.     

Development of an Easy Multiresidue Method for Fat-Soluble Pesticides in Animal Products Using Gas Chromatography–Tandem Mass Spectrometry

The determination of pesticide residues in animal samples requires several analytical steps which may be time-consuming extraction procedures and with a small scope. For fat-soluble pesticides, the determination of fat is essential as they tend to bioaccumulate in fat. As to address these concerns, an easy acetonitrile-based multiresidue method combined with GC-MS-MS technology for the determination of the fat-soluble analytes was developed and validated on animal products. Analytes from several chemical classes such as diphenyl ethers, pyrethroids, organochlorides, triazoles, carbamide, chlorophenyls, dinitroaniline, organophosphorus, chloroacetamides, benzamides, aromatic hydrocarbon and dicarboximide known, due to their fat-soluble property, to bioaccumulate in animal tissues were selected. The method showed acceptable linearity (r?≥?0.99) and accuracy with recoveries between 70 and 120 % and precision with SD_R?≤?20 % for the majority of the analytes studied. For the analytes that presented accuracy and precision values outside the acceptable limits, the method still is able to serve as a semi-quantitative method. The contribution of the determination of the fat in the results was also investigated. The limit of detection was set at 0.003 mg/kg. The proposed methodology was applied to meat and offal samples from the regional market in Attiki (Greece).     

Determination of the Nicotine Content in Solanaceae Vegetables by Solid-Phase Extraction Coupled with Ultra High-Performance Liquid Chromatography–Tandem Mass Spectrometry

A validated method based on solid-phase extraction and ultra high-performance liquid chromatography–triple quadrupole tandem mass spectrometry, with electrospray ionization operated in the positive ion mode and multiple reaction monitoring, was developed for the determination of nicotine in Solanaceae vegetables. Sample preparation involved liquid–solid extraction, centrifugation, filtration, and solid-phase extraction. Two kinds of solid-phase extraction adsorbents, based on different retention mechanisms, were investigated. Relatively higher recoveries were obtained with a hydrophilic–lipophilic-balanced cartridge. A deuterated internal standard was used for quantification. The limit of quantification (LOQ) of nicotine in different vegetables was found to be between 0.07 and 0.5 μg/kg. The nicotine levels in the vegetable samples were above the LOQs. The method described here is thus suitable for the analysis of large sample batches, because it provides accurate quantification, high sensitivity and rapid chromatographic separation with facile preparation. The solid-phase extraction cartridges and organic solvents used in this work are easy to obtain, enabling the application of this method in most analytical laboratories.     

Quantitative Determination and Confirmation of Five Synthetic Glucocorticoid Residues in Milk Powder by Gel Permeation Chromatography–Liquid Chromatography–Tandem Mass Spectrometry

A new method for multi-residue determination of five synthetic glucocorticoids (betamethasone, dexamethasone, prednisone, prednisolone, and hydrocortisone) in milk powder is developed. The glucocorticoids in the samples were extracted with tert-butyl methyl ether under ultrasonication incubation, and then cleaned up through gel permeation chromatography. After C18 LC gradient elution separation using acetonitrile with 0.1% formic acid as a mobile phase, the eluents were determined by liquid chromatography–tandem mass spectrometry with multiple reaction monitoring and positive ionization modes. The effective separation for the five glucocorticoids was achieved. The limit of quantification of the method for testing five glucocorticoids in milk powder was in the range from 0.2 to 0.5 μg kg⁻¹, which was lower than the maximum residue limits established by European Union for glucocorticoids in foods. Experiments on spiked samples of milk powder showed that the mean recoveries at addition level of 1.0, 3.0, and 5.0 μg kg⁻¹ were in the range of 71.2% and 103%, and the relative standard deviation ranged from 4.7% to 16.8%. The calibration curves for these drugs between 1.0 and 100 μg l⁻¹ showed good linearity, with correlation coefficient (r) more than 0.999. The real sample test showed that this method is sensitive and accurate. It can be used for qualitative and quantitative determination of studied glucocorticoid residues in milk powder samples.     

Determination of Pydiflumetofen Residues in Some Foods of Plant and Animal Origin by QuEChERS Extraction Combined with Ultra-Performance Liquid Chromatography–Tandem Mass

A rapid and effective analytical method for determination of pydiflumetofen residues in some foods of plant and animal origin (grapes, tomatoes, wheat, pork, milk, and eggs) was developed using a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation procedure followed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS). Acetonitrile was served as the extraction solvent, and an octadecylsilane-dispersive solid-phase extraction (C18-dSPE) was used to cleanup the analyte, and then detected by UPLC–MS/MS. Pydiflumetofen was eluted within 3.0 min from the HSS T3 chromatography column connected to an electrospray ionization source in positive mode. The linearity of the method was excellent (R²?≥?0.992) in the pydiflumetofen concentration range of 10–1000 μg kg^?1. The recoveries of spiked pydiflumetofen (10, 100, and 1000 μg kg^?1) from the matrices were satisfactory, being between 72.0 and 110.3%, and all with relative standard deviation values of <?15.1%. The limit of quantification for pydiflumetofen was 10 μg kg^?1. This study provides a method for the routine monitoring of pydiflumetofen.     

Liquid Chromatography–Tandem Mass Spectrometry Multiclass Method for 46 Antibiotics Residues in Milk and Meat: Development and Validation

A screening method for analysis of 46 antibiotics residues, belonging to different classes, such as tetracyclines, sulfonamides, fluoroquinolones, β-lactams, cephalosporins, macrolides and other minority groups was developed and validated for application in bovine milk and bovine, swine, poultry, equine, fish and shrimp meat samples. Sample preparation consists in solvent extraction followed by clean up with C18 bulk and low temperature purification. Instrumental analysis was performed using liquid chromatography coupled to tandem mass spectrometry system. Chromatographic separation was achieved using a C18 column. Mobile phase was composed by methanol and water. The method was validated according to Commission Decision 2002/657/EC criteria. Validation parameters such as specificity and detection capability (CCβ) were determined and considered suitable to the established criteria. Values of CCβ ranged from 1.0 to 50.0 μg L^?1 or μg Kg^?1, depending on the compound and the matrix. The proposed method has been applied into Brazilian National Residue Control Plan since 2013 for the determination of antibiotic residues. A total of 3833 samples were analyzed until the current date and 13 samples showed positive results with concentrations above the permitted. The method is fast, easy and adequate for high throughput analysis in routine laboratories.     

Optimization of Headspace Single-Drop Microextraction Coupled with Gas Chromatography–Mass Spectrometry for Determining Volatile Oxidation Compounds in Mayonnaise by Response Surface Methodology

In this assay, headspace single-drop microextraction (HS-SDME) coupled with gas chromatography–mass spectrometry (GC–MS) as a simple, low-cost and rapid method has been developed and validated for determining volatile oxidation compounds including hexanal and heptanal in mayonnaise. The main microextraction variables affecting the HS-SDME procedure such as extraction temperature and time, stirring rate, and amount of NaCl were optimized by response surface methodology employing a central composite design. Obtained results demonstrated that higher yield of extracted analytes could be achieved under the following optimal conditions: extraction temperature of 45 °C, extraction time of 16 min, stirring rate at 700 rpm, and addition of 2 g NaCl. The optimized HS-SDME/GC–MS method was validated for oxidized mayonnaise samples (50 °C/48 h) by calculating analytical parameters (linearity, precision, accuracy, and sensitivity). Good linearity (R ²?>?0.99) was observed by plotting calibration curves of extracted hexanal and heptanal over the concentration range of 0.025–10 μg g^?1, and the repeatability of the method, expressed as relative standard deviation, were found to be 4.04 % for hexanal and 3.68 % for heptanal (n?=?7). After the microextraction process of spiked mayonnaise sample, high levels of relative recovery were obtained for hexanal (107.33 %) and heptanal (91.43 %). The detection limits were 0.008 ng g^?1 and 0.021 ng g^?1 for hexanal and heptanal, respectively, while quantification limits of hexanal and heptanal were calculated to be 0.027 ng g^?1 and 0.071 ng g^?1, respectively. The possibility of the HS-SDME followed GC–MS to determine and quantify volatile oxidation compounds such as hexanal and heptanal was confirmed by analyzing commercial fresh mayonnaise stored at 4 and 25 °C during 3 months.     

Quantitation of Selected Polyphenols in Plant-Based Food Supplements by Liquid Chromatography–Ion Trap Mass Spectrometry

A high-performance liquid chromatography method with electrospray ionization mass spectrometric detection (HPLC-ESI-MS/MS) for the determination of some of the most important polyphenols present in botanical supplements has been developed. The target analytes were five flavonoids (diosmin, hesperidin, quercetin, rutin and troxerutin) and the flavolignan silybin. The extraction of the analytes from the supplements was carried out by ultrasound-assisted extraction using 100 % dimethyl sulfoxide (or methanol) for 15 min. After centrifugation, 1 μL of the diluted supernatant was injected in the HPLC system and the quantitation was performed by ESI-MS using the negative ionization mode, with methylparaben as internal standard. The validation of the method was performed with recovery experiments, observing recoveries in the range of 85–112 %, and relative standard deviations lower than 10 % for the complete analytical procedure, including the extraction. The limits of detection were in the 2.5–120 μg L^?1 range.     

A Rapid and Sensitive Method for Determination of Melamine in Fish,Shrimp, Clam,and Winkle by Gas Chromatography–Mass Spectrometry with Microwave-Assisted Derivatization

A method for rapid and sensitive determination of melamine in aquatic products by gas chromatography–mass spectrometry with microwave-assisted derivatization was proposed in this paper. Melamine was extracted from aquatic product samples using methanol, and the extract was cleaned with a mixed-mode cationic exchange solid phase extraction column. After elution with 5 % ammonia–methanol solution and drying with nitrogen, the residue was derivatized using N,O-bis(trimethylsilyl)trifluoroacetamide containing 1 % trimethylchlorosilane under microwave irradiation for 1 min with a power of 420 W, then detected with gas chromatography–mass spectrometry, and quantified by the external standard method. Some important parameters such as extraction solvent, microwave irradiation power and time, and derivatization reagent volume were investigated and optimized. The results showed that methanol could effectively extracted melamine from aquatic products as well as precipitated the protein in samples. Under the optimum conditions, the detection limit for melamine was as low as 0.006 mg/kg, and the linear range was from 0.02 to 50 mg/kg with a correlation coefficient of 0.9997. The proposed method was applied to the analysis of melamine in aquatic products (fish, shrimp, clam, and winkle), and the recovery for melamine was 89.65–105.16 % with relative standard deviation of 3.0–6.0 %.