On-line Solid-Phase Extraction Coupled to Liquid Chromatography–Ion Trap Tandem Mass Spectrometry for Determination of Penicillins in Catfish

A highly selective method was developed for the simultaneous determination of eight penicillins in catfish using automated on-line solid-phase extraction coupled to liquid chromatography–tandem mass spectrometry (XLC–MS/MS). The type of cartridge, equilibration sample volume, volume of solvent to carry the sample into the cartridge, and elution times were studied in order to optimize the XLC operating conditions. MS/MS conditions were also adjusted for better peak resolution. The present method was validated in agreement with the criteria of Commission Decision 2002/657/EC, showing a linear range from 2 to 350 μg kg⁻¹ and regression coefficient higher than 0.995 for the studied penicillins. Decision limits, calculated in the case of substances with no permitted limit, were lower than 0.6 μg kg⁻¹, and detection capability values were lower than 2.0 μg kg⁻¹. Samples spiked at 2.0, 10.0, and 50.0 μg kg⁻¹ showed high recovery (72–92%) and precision values lower than 20% except for amoxicillin. The present method was also applied for the analysis of penicillins in 30 catfish samples bought in local markets.     

Dispersive Liquid–Liquid Microextraction Followed by Magnetic Solid-Phase Extraction for Determination of Four Parabens in Beverage Samples by Ultra-performance Liquid Chromatography Tandem Mass Spectrometry

In this study, a two-step extraction technique was developed for extraction and preconcentration of parabens from beverage samples using ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) and magnetic solid-phase extraction (MSPE). In this IL-DLLME followed by MSPE method, ionic liquid (IL, 1-octyl-3-methylimidazolium hexafluorophosphate) formed hydrophobic microdroplets in beverage samples as an extractant of parabens; after the IL-DLLME process was completed, graphene modified Fe₃O₄ nanoparticles (Fe₃O₄@G) were placed to adsorb and isolate IL from the sample solution. After the supernatant was carefully moved, acetonitrile was added to elute the IL containing parabens from Fe₃O₄@G. The experimental variables affecting the extraction procedure have been systematically studied. Under optimal conditions, the detection limits were less than 1.53 ng/mL and the linear detection ranges were 2–500 ng/mL (R ² ≥ 0.998) for these analytes. The recoveries for spiked samples were 58.8–89.2% and satisfactory precision (RSD ≤ 4.8%) were obtained.     

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 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 23 Dyes in Chili Powder and Paste by High-Performance Liquid Chromatography–Electrospray Ionization Tandem Mass Spectrometry

A sensitive and comprehensive method was developed to determine 23 prohibited dyes in chili powder and paste by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry. Target compounds were simultaneously extracted from chili samples with acetonitrile and purified using freezing-lipid filtration. Chromatographic separation was achieved on a Waters UPLC BEH C18 column (100× 2.1 mm, 1.7 μm) with gradient elution. Detection and quantification were performed using mass spectrometry in multiple reaction monitoring mode. The method was validated for selectivity, linearity, recovery, precision, and limit of quantification (LOQ), using spiked chili powder and paste samples. The average recoveries of analytes were 58.6–122.1%, with relative standard deviations between 1.0% and 18.9%. The LOQs ranged from 0.2 to 50 μg/kg. This method was successfully applied to chili powder and paste obtained from local markets. Chrysoidine, Rhodamine B, Orange II, and Sudan I and IV were detected in several samples.     

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.     

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.     

Determination of Triazoles in Tea Samples Using Dispersive Solid Phase Extraction Combined with Dispersive Liquid–Liquid Microextraction Followed by Liquid Chromatography–Tandem Mass Spectrometry

In this study, dispersive solid phase extraction (DSPE) combined with dispersive liquid–liquid microextraction (DLLME) method was developed for the determination of triazole fungicide residues in tea samples. DSPE with ODS C₁₈, primary secondary amine, and florisil as sorbents was applied to clean up and minimize matrix interference from tea samples; it was followed with the enrichment of target compounds in the DLLME procedure and detection with liquid chromatography–tandem mass spectrometry (LC-MS/MS). The effects of various experimental parameters on the DSPE and DLLME procedures were studied systematically, such as the kinds and volume of sorbents, extraction and dispersive solvents, and extraction time. Under optimum conditions, the method was validated in a tea matrix. The matrix-matched calibration curves of three triazoles had good linearity in the range of 0.0125–50 μg kg^?1, and the linear regression coefficients (r) ranged from 0.9998 to 0.9999. The limits of quantification (S/N?=?10) for penconazole, tebuconazole, and triadimenfon were 4.0, 7.8, and 31.6 ng kg^?1, respectively. The intra-day and inter-day relative standard deviations varied from 3.6 to 18.6 %. Recoveries in three concentration levels were between 91 and 118 %. The obtained results show that the proposed DSPE-DLLME-LC-MS method has the potential to analyze trace fungicides in a complex sample matrix.     

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 %.     

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.     

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.     

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.     

Simultaneous Determination of Triclabendazole and its Metabolites in Bovine and Goat Fat Tissues by Liquid Chromatography–Tandem Mass Spectrometry

A sensitive and reliable method for the simultaneous determination of triclabendazole, its main metabolites (triclabendazole sulfone and triclabendazole sulfoxide) and a marker residue (ketotriclabendazole) in edible ruminant fat tissues is developed and validated. Analytes are extracted from fat tissues with acetonitrile, and crude extracts are subjected to liquid?Cliquid extraction with n-hexane. Chromatographic separation is performed on a C₁₈ reversed-phase column with gradient elution. Analytes are detected by tandem quadrupole mass spectrometry after positive electrospray ionization by multiple reaction monitoring. Relative recoveries from spiked samples range from 86.1% to 114.3%, with relative standard deviations generally below 13.8%. Limits of detection and quantification for analytes are within 0.125?C1.25???g/kg and 0.5?C5???g/kg, respectively. The method proposed in this study was successfully applied to real sample testing.     

One-Step QuEChERS-Based Approach to Extraction and Cleanup in Multiresidue Analysis of Sulfonylurea Herbicides in Cereals by Liquid Chromatography–Tandem Mass Spectrometry

A one-step quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based approach to extraction and cleanup in multiresidue pesticide analysis is presented for the first time. The experiment was designed to detect 23 sulfonylurea herbicides in a complex cereal matrix. The challenge was to choose the optimal conditions of one-step extraction and cleanup. Chitin, diatomaceous earth, and octadecyl were investigated as cleanup sorbents. Chitin, citrate buffer, and 1 % formic acid in acetonitrile yielded the best results. The effectiveness of sulfonylureas extraction was evaluated at three different spiking levels (0.005, 0.05, and 0.5 mg kg^?1) in wheat, rye, and oat using liquid chromatography–tandem mass spectrometry. The one-step QuEChERS provided recoveries in the 70–120 % range for 23 sulfonylureas in all cereal matrices. Matrix effects were evaluated and were not significant for all herbicides, showing suppression or enhancement (between ?19 and 13 %). Precision, calculated as relative standard deviation (RSD), was below 20 %. A linear dependence was observed in the range of 0.005–2.0 mg kg^?1, and the correlation coefficient was R ² > 0.999. Expanded measurement uncertainty was estimated to be between 9 and 24 %, on average. The validated method was employed in analysis of 89 real grain samples.     

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 %.     

Trace Analysis of Seven Neonicotinoid Insecticides in Bee Pollen by Solid–Liquid Extraction and Liquid Chromatography Coupled to Electrospray Ionization Mass Spectrometry

A new, fast, simple, and efficient sample treatment to extract seven neonicotinoid insecticides (acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam) in corbicular bee pollen has been developed. This procedure consisted of a solid–liquid extraction of the neonicotinoids from pollen with dichloromethane, followed by evaporation and reconstitution. Once the neonicotinoids were extracted, they were determined using a liquid chromatography coupled to an electrospray ionization mass spectrometry method. The method was validated in terms of selectivity, linearity, precision and recovery. The limits of detection and quantification were 0.4–2.8 μg/kg and 1.2–9.1 μg/kg, respectively, and the extraction recoveries were between 86 and 106 % in all cases. Finally, the proposed method was applied to analyze bee pollen samples collected from apiaries located close to fruit orchards in two Spanish regions, and traces of acetamiprid and imidacloprid were found in two samples.     

Determination of 103 Pesticides and Their Main Metabolites in Animal Origin Food by QuEChERS and Liquid Chromatography–Tandem Mass Spectrometry

A rapid and sensitive analytical multiresidue method has been developed for the simultaneous determination of 103 pesticides (herbicides, insecticides, and fungicides) and 18 metabolites in foods of animal origin using liquid chromatography-tandem with triple quadrupole in dynamic multiple reaction monitoring (DMRM) mode. A modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) sample preparation technique was established, and the efficiency of the dispersive solid-phase extraction (d-SPE) cleanup step was evaluated by comparing the effects of different d-SPE sorbent combinations (primary secondary amine (PSA) + graphitized carbon black (GCB), PSA + C18, C18, and C18 + GCB). The limits of quantification (LOQs) ranged from 1 to 10 μg/kg, and the coefficient of determination (R ²) was ≥0.995 within the calibration linearity range of 0–250 μg/L for all pesticides. The combination of C18 + GCB was validated at two spiking levels (10 and 50 μg/kg) in chicken, fish, pork, and rabbit. Satisfactory recoveries (70–119%) and RSDs ≤17% were achieved for all analytes, except for naptalam (60–69%), pyrimethanil (40–49%), and thiabendazole (62–66%) at 10 μg/kg spiking level. The validated method was successfully applied to the analysis of real samples of food of animal origin.     

Simultaneous Determination of 15 Plant Growth Regulators in Bean Sprout and Tomato with Liquid Chromatography–Triple Quadrupole Tandem Mass Spectrometry

The present paper describes the development and validation of a new reversed-phase liquid chromatography–electrospray ionization tandem mass spectrometric method for determination of 15 plant growth regulators in bean sprout and tomato. Plant growth regulators were extracted with mixed solvents methanol/acetonitrile/water/acetic acid (v/v/v/v, 40/40/20/1) from 10 g vegetable and analyzed directly without further cleanup. The identification of each analyte was established by chromatographic retention time, analyte-specific fragmentation patterns, and relative peak area ratios of precursor/product ion pairs. The recoveries of 15 plant growth regulators in bean sprout and tomato were 70.3–110.0 %. The repeatability of this method is excellent, and relative standard deviation value is less than 10 %.     

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.