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.     

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.     

Investigation of Levels and Fate of Pyridalyl in Fruit and Vegetable Samples by Fast Gas Chromatography–Mass Spectrometry

The search on pyridalyl residues, the novel insecticide, in strawberries and spring onions was evaluated. The QuEChERS technique was used for sample preparation. A fast gas chromatography–mass spectrometry (GC–MS) method was developed and validated for the analysis of pyridalyl in both matrices. Fast GC–MS was performed with a narrow-bore capillary column and a quadrupole mass detector with electron ionization and negative chemical ionization, both operating in selected ion monitoring mode. Fortification studies at 1, 5, 10, and 250 μg/kg for fruit and vegetable matrices were performed. Recoveries for all fortification levels, two ionization modes ranged from 72 to 114 %. Matrix effects were discussed. Limits of quantification were established at 1 μg/kg. Field experiments to investigate the pre-harvest interval were carried out. The proposed method was applied successfully to the determination of pyridalyl residues in samples available on Slovak market, and none of the samples contained detectable amounts of pesticides. The developed method is simple, efficient, and easy to adopt in laboratories engaged in pesticide residue analysis method.     

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.     

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 %.     

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.     

Application of Matrix Solid-Phase Dispersion and Liquid Chromatography–Ion Trap Mass Spectrometry for the Analysis of Pesticide Residues in Fruits

This study presents an application of rapid and sensitive multiresidue method for the analysis of acephate, acetamipride, atrazine, carbendazim, carbaryl, carbofuran, dimethoate, imidacloprid, linuron, malathion, monocrotophos, monuron, propazine, simazine, and tebufenozide in fruits. The method involves an extraction procedure based on matrix solid-phase dispersion using diatomaceous earth as a dispersant and dichloromethane as the eluent. The target pesticides were determined using liquid chromatography–ion trap mass spectrometry. Quantification of the analytes was carried out using the most sensitive ion transition. Ion trap parameters, like activation q and time, were found to have a prominent influence on method sensitivity for some pesticides and they were optimized accordingly. The confirmation of residues detected in real samples was performed by repeated injection and acquiring additional ion transitions besides the ones used for quantification. The method was validated for accuracy, linearity, reproducibility, and sensitivity. Mean values for recoveries were in the range of 70–120 % for all tested matrices. Repeatability of the method, expressed as the relative standard deviation, was in general lower than 20 %. The applicability of the method to routine analysis was tested in real fruit samples with good performance.     

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.     

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.     

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 %.     

Gas Chromatography–Mass Spectrometry Analysis and Chemical Composition of the Bamboo-Carbonized Liquid

Bamboo plant is native to Asia and a popular ingredient in Asian dishes. Bamboo distillate solution has mild acidic pH of 3.0. GC–MS analysis has been done, and 43 compounds have been identified. The percentage composition of phenolic compounds, aromatic hydrocarbons, and other ingredients are identified in the acidic bamboo distillate by ether extraction method.     

Multi-residual Pesticide Monitoring in Commercial Chinese Herbal Medicines by Gas Chromatography–Triple Quadrupole Tandem Mass Spectrometry

To investigate multi-residual pesticide monitoring data in commercial Chinese herbal medicines on major markets, an easy, rapid, and selective gas chromatography with mass spectrometry (GC/MS/MS) method was established for simultaneously determining multi-residual pesticides including organochlorine, pyrethroid, carbamate, and organophosphorus pesticides in Chinese herbal medicines. The analytical method was based on an efficient extraction procedure and further cleanup steps by solid-phase extraction columns, yielding recovery rates in the range of 70.0–120.0 % for the majority of pesticides, except for hexachlorobenze, diazinon, β-HCH, δ-HCH, and omethoate, with precision values expressed as relative standard deviation of 0.1–14.7 %. The limits of detection of the established GC/MS/MS method for all investigated pesticides ranged from 0.01 to 3.6 μg kg^?1 and limits of quantification from 0.03 to 11.88 μg kg^?1. With this validated method, multi-residual pesticides of 132 Chinese herbal medicine samples were analyzed. The monitoring results indicated that pesticide residue was found in 74 samples. In total, 51 pesticides were found with detection rate ranging from 0.76 to 18.94 %. An 82.3 % of positive pesticides were found in less than 6 % of samples. Hexachlorobenzene was found in 25 samples, quintozene in 15 samples, and acephate and simazine in 13 samples. Concentrations of pesticide residue from monitoring data obtained ranged from 0.5 to 203.5 μg kg^?1. The simple and rapid method can be used as routine analysis method in multi-residual pesticide monitoring of Chinese herbal medicines.     

Analysis of Infant Formula for Steroid Hormones by Gas Chromatography–Tandem Mass Spectrometry Using Microwave-Assisted Extraction and Gel Permeation Chromatography Clean Up

A new method was developed for effective separation and simultaneous determination of estrogens, gestagens, and androgens, including estrone, 17β-estradiol, testosterone, progesterone, and estriol, in infant formula. The samples were enzymatically digested with β-glucuronidase/arylsulfatase prior to microwave-assisted extraction. After the extract was cleaned up by gel permeation chromatography the hormones were derivatived with 50 μL BSTFA containing 1 % TMCS. The derivatived hormones were measured with GC–MS/MS using electron impact ionization source in the positive multi-reaction monitoring mode. The calibration curves showed good linearity with correlation coefficient (r) of >0.999. The limit of quantification of five hormones ranged from 0.094 to 0.265 μg kg^?1, which is below the minimum required performance limits established by the European Community. The intra- and inter-day precision (as RSD) for six determinations of five analytes at 40 μg kg^?1 spiked level was in range of 3.4–5.4 % and 3.5–6.8 %, respectively. The recovery of five analytes was obtained to be 84.5–104 %, with relative standard deviations (RSD, n?=?6) of 1.7–5.5 %. This method has been successfully used for the qualitatively and quantitatively determination of estrone, 17β-estradiol, testosterone, progesterone, and estriol in infant formula.     

Fast Preconcentration of Pesticide Residues in Oilseeds by Combination of QuEChERS with Dispersive Liquid–Liquid Microextraction Followed by Gas Chromatography-Mass Spectrometry

A fast, efficient, and simple method for determination of pesticide residues in pumpkin seeds has been developed combining QuEChERS and dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography and mass spectrometry (GC-MS). Parameters affecting the DLLME performance such as solvent selection and volume of extractive and dispersive solvent, salt effect, and extraction time were studied. Under the selected conditions (50 μL extractive solvent chloroform, 1 mL QuEChERS extract, and 3 mL water), the developed method was validated. Linearity was evaluated at nine concentrations in the broad range of 0.1–500 μg/kg with correlation coefficients from 0.9842 to 0.9972. The relative standard deviations at lowest calibration level varied from 0.3 to 22 %. Under the optimum conditions, an enrichment factor was 6–17-fold and detection limits 0.01–12.17 μg/kg were achieved. Finally, the developed and validated method was successfully applied for the extraction and determination of pesticide residues in 16 real samples with 2 positive findings below maximum residue limits (MRL). Limits of detection (LODs) of the proposed method are below the MRLs established by the European Union.     

A New Extraction Method for the Determination of Oxytocin in Milk by Enzyme Immune Assay or High-Performance Liquid Chromatography: Validation by Liquid Chromatography–Mass Spectrometry

There has been a controversy regarding the use of exogenous oxytocin (OT) in milking cattle which may have toxicological consequences during nonphysiological exposure. In the present study, a new sensitive extraction method for OT was developed followed by enzyme immune assay (EIA) or high-performance liquid chromatography (HPLC) analysis. The extraction of OT in milk involves two steps: (1) TCA precipitation of milk proteins and (2) solid-phase extraction (SPE) cleanup process. Without these steps, analysis of OT in milk was not possible. Utilizing EIA as a quantitative tool the limit of detection (LOD) and limit of quantitation (LOQ) were found to be 7.74 and 10.3 pg?ml^?1, precision in terms of intra- and interday coefficient of variation was below 13 % (%RSD, N?=?8), while percent recoveries were between 85 and 92 %. Utilizing UV-HPLC, the LOD, LOQ, precision, and recovery values were found to be 4.1 ng?ml^?1, 9.8 ng?ml^?1, 2–10 %, and 84–91 %, respectively. OT was found to be stable against adverse temperature (up to 100 °C) and pH (2 to 10) and simulated gastric fluid digestibility assay. Four milk samples collected from the market were analyzed, which showed that TCA precipitation and SPE steps are mandatory and the results were validated by LC-MS showing mass ion peak at 1 kD.     

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.     

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.     

Determination of Triazole Fungicides in Vegetable Samples by Magnetic Solid-Phase Extraction with Graphene-Coated Magnetic Nanocomposite as Adsorbent Followed by Gas Chromatography–Mass Spectrometry Detection

A graphene-based magnetic nanocomposites (G-Fe₃O₄ MNPs) was synthesized and used as the adsorbent for the extraction of some triazole fungicides (triadimefon, paclobutrazol, hexaconazole, myclobutanil, diniconazole, propiconazole, and tebuconazole) in cucumber, cabbage, and tomato samples prior to gas chromatography–mass spectrometry detection. Various experimental parameters affecting the extraction efficiencies, such as the amount of G-Fe₃O₄ MNPs, extraction time, pH and salt concentration of the sample solution, and desorption conditions were investigated. Under the optimized experimental conditions, the enrichment factors of the method for the analytes were in the range from 461 to 697. The signal response was linear in the range of 0.5–35.0 ng g^?1 for all the analytes with the correlation coefficients ranging from 0.9810 to 0.9986. The limits of detection (S/N?=?3) of the method for the analytes were between 0.01 and 0.10 ng g^?1. The recoveries of the method for the seven triazoles were in the range from 84.4 to 108.2 % with RSDs between 3.4 and 10.6 %.     

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.     

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.