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.     

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 %.     

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.     

Application and Optimization of Microwave-Assisted Extraction and Dispersive Liquid–Liquid Microextraction Followed by High-Performance Liquid Chromatography for the Determination of Oleuropein and Hydroxytyrosol in Olive Pomace

In the present study, a new method based on microwave-assisted extraction and dispersive liquid–liquid microextraction (MAE–DLLME) followed by high-performance liquid chromatography (HPLC) was proposed for the separation and determination of oleuropein (Ole) and hydroxytyrosol (HyT) from olive pomace samples. The effective factors in the MAE–DLLME process such as microwave power, extraction time, the type and volume of extraction, and dispersive solvents were studied and optimized with the aid of response surface methodology (RSM) based on a central composite design (CCD) to obtain the best condition for Ole and HyT extraction. At the optimized conditions, parameter values were 220 W microwave power, 12 min extraction time, 60 μL extracting solvent, and 500 μL dispersive solvent. The calibration graphs of the proposed method were linear in the range of 10–500,000 μg L^?1, with the coefficient of determination (R²) higher than 0.99 for Ole and HyT. Repeatability of the method, described as the relative standard deviation (RSD), was 4.12–5.63% (n?=?6). The limits of detection were 35 and 20 μg L^?1 for Ole and HyT, respectively. The recoveries of these compounds in the spiked olive pomace sample were from 93 to 98%. The proposed method, MAE–DLLME–HPLC–UV, was an accurate, rapid, and reliable method when compared with previous methods.     

Extraction and Preconcentration of Some Triazole Pesticides in Grape Juice by Salting Out Homogeneous Liquid–Liquid Extraction in a Narrow-Bore Tube Prior to Their Determination by Gas Chromatography–Flame Ionization Detection

A fast and simple extraction and preconcentration method for some triazole pesticides has been developed using a homogeneous liquid–liquid extraction method performed in a narrow-bore tube. The extraction is based on phase separation of a water-miscible organic solvent from aqueous solution in the presence of a salting out agent. In this work, the homogeneous solution of water and acetonitrile (water-soluble extraction solvent) was broken by addition of 30 %, w/v, sodium chloride (salting out agent). After sonication, a small volume of acetonitrile was collected on top of the tube and the extracted analytes in the collected phase were determined by gas chromatography–flame ionization detection. The effect of various experimental parameters including kind and volume of the water-soluble organic solvent, amount of salt, length and diameter of tube, and pH of sample solution was investigated. Under the optimum conditions, calibration graphs were linear over the range of 3–5,000 μg L^?1. Relative standard deviations were less than 5.4 % for six repeated determinations (C?=?100 μg L^?1). Furthermore, the limits of detection (S/N?=?3) and quantification (S/N?=?10) were obtained in the ranges of 0.60–4.8 and 1.9–16 μg L^?1, respectively. This method is very simple and rapid, requiring less than 10 min for sample preparation. It has been successfully utilized for the analysis of triazole pesticides in the grape juice samples.     

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.     

Development of Multiresidue Analysis for 21 Synthetic Colorants in Meat by Microwave-Assisted Extraction–Solid-Phase Extraction–Reversed-Phase Ultrahigh Performance Liquid Chromatography

A novel ultrahigh performance liquid chromatographic method is developed for analysis of 21 synthetic colorants with different acid–base property, solubility, and polarity. The meat samples were extracted by microwave-assisted extraction followed by cleanup with solid-phase extraction. The effective separation of the colorants in meat matrixes was achieved, and no interfering peaks could be detected at the retention time of the analytes. The calibration curves showed good linearity with correlation coefficients of 0.9940–0.9999. The limits of quantification were 0.48–7.19 μg/kg. The average recovery of the 21 analytes from meat samples spiked with 25 and 75 μg?kg^?1 was 61.29–116.1 % with relative standard deviation (RSD) of <11 %. For blank beef sausage spiked with 50 μg?kg^?1 for each analyte, the intraday precision (as RSD) for 21 analytes was 1.45–9.21 % for six determinations within a day. This method has the advantages of being rapid, sensitive, accurate, and with high-throughput and can be applied for multiresidue analysis of meat samples, including six allowable azo food colorants, ten banned azo food colorants, four banned triphenylmethanes, and rhodamin B food colorant.     

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 HMF in Vinegar and Soy Sauce Using Two-Step Ultrasonic Assisted Liquid–Liquid Micro-Extraction Coupled with Capillary Electrophoresis-Ultraviolet Detection

A new, rapid, and inexpensive method using two-step ultrasonic assisted liquid–liquid micro-extraction (UALLME) coupled with capillary electrophoresis-ultraviolet (CE-UV) was developed for 5-hydroxymethylfurfural (HMF) analysis in high ion strength samples (like vinegar and soy sauce). The factors affecting the extraction efficiency were optimized such as the extraction volume, the ultrasonic time, and the power density of ultrasonic. Under the optimum conditions, the limit of detection (LOD) and the limit of quantification (LOQ) for HMF were 0.03 and 0.10 mg/L, respectively. The relative standard deviations (RSD %) for HMF were ranging from 0.53 to 3.17%, and the recoveries of HMF were ranging from 91.24 to 109.39%. The results turned out that two-step UALLME-CE-UV was applicable to analyze HMF in vinegar and soy sauce. Eleven brands of vinegar and soy sauce were tested by two-step UALLME-CE-UV, and the results showed that the method had a potential application in analysis of foodstuffs. The two step UALLME method was effective to improve the selectivity and sensitivity of CE-UV method for HMF analysis in vinegar and soy sauce.     

Ion-Pair-Based Air-Assisted Liquid–Liquid Microextraction for the Extraction and Preconcentration of Phthalic Acids from Aqueous Samples

In the present study, a rapid, simple, and highly efficient sample preparation method based on ion-pair air-assisted liquid–liquid microextraction using a low-density extraction solvent followed by high performance liquid chromatography–diode array detection has been developed for the extraction, preconcentration, and determination of three phthalic acids (phthalic acid, iso-phthalic acid, and terephthalic acid) in aqueous samples. In this method, a mixture of tri-butyl amine (as an ion-pair reagent) and toluene (as an extraction solvent) is transferred into an aqueous sample solution. Fine organic solvent droplets are formed by aspirating and dispersing of the mixture via syringe needle. After that, the formed ion-pairs are extracted into toluene, and after centrifuging, the obtained collected phase is transferred into a microtube and is evaporated to dryness under a stream of nitrogen at room temperature. The residue is re-dissolved in mobile phase and injected into the separation system for analysis. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.09–0.24 and 0.29–0.78 ng mL^?1, respectively. Extraction recoveries and enrichment factors were from 88 to 98 % and 443 to 491, respectively. Relative standard deviations for the extraction of 5 ng mL^?1 of each analyte were less than 8.4 % for intra-day (n?=?6) and inter-days (n?=?5) precisions. Finally, different aqueous samples were successfully analyzed using the proposed method, and the target analytes were determined in some of them at ng mL^?1 level.     

Optimized Dispersive Liquid–Liquid Microextraction and Determination of Sorbic Acid and Benzoic Acid in Beverage Samples by Gas Chromatography

A new rapid method for direct determination of trace levels of sorbic and benzoic acids was developed by dispersive liquid–liquid microextraction and gas chromatography with flame ionization detection. In the proposed approach, the separation procedure of sorbic and benzoic acids was performed on a general chromatographic column without any prior derivatization processes. Some effective parameters on the microextraction recovery were studied and optimized utilizing multilevel factorial and central composite experimental designs. The best concurrent extraction efficiency acquired using ethanol and chloroform as dispersive and extraction solvents. Central composite design (CCD) resulted in the optimized values of microextraction parameters as follows: 1.0 mL of dispersive and 0.1 mL of extraction solvents, ionic salt concentration of 50 g?L^?1 at pH 4. Under optimum conditions, the calibration curve was linear over the range 0.5–20 mg L^?1. Relative standard deviation was 11% and 13% for five repeated determinations for sorbic and benzoic acids, respectively. Limits of detection were acquired as 0.2 mg L^?1 for sorbic acid and 0.5 mg L^?1 for benzoic acid. The average recoveries were 31% and 39% for sorbic and benzoic acids, respectively. The method was successfully applied to the determination of sorbic and benzoic acids as preservatives in beverage samples.     

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.     

Ultrasound-Assisted Extraction Followed by Solid-Phase Extraction Followed by Dispersive Liquid–Liquid Microextraction for the Sensitive Determination of Diazinon and Chlorpyrifos in Rice

Selectivity of solid-phase extraction (SPE) was combined with the concentration power of dispersive liquid–liquid microextraction (DLLME) to obtain a sensitive, low solvent consumption method for high-performance liquid chromatography determination of diazinon and chlorpyrifos in rice. In this method, rice samples were extracted by ultrasound-assisted extraction followed by SPE. Then, the SPE eluent was used as a disperser solvent in the next dispersive liquid-liquid microextraction step for further purification and enrichment of diazinon and chlorpyrifos. Under the optimal conditions, the linear range was from 5.0 to 250 μg kg^?1 for diazinon and from 2.5 to 250 μg kg^?1 for chlorpyrifos. Limits of detection of diazinon and chlorpyrifos were 1.5 and 0.7 μg kg^?1, respectively. Limits of quantitation of diazinon and chlorpyrifos were 5.5 and 3.0 μg kg^?1, respectively. The precisions and recoveries also were investigated by spiking 10 μg kg^?1 concentration in rice. The recoveries obtained were over 90 % with relative standard deviation (RSD%) below 9.0 %. The new approach was utilized to successfully detect trace amounts of diazinon and chlorpyrifos in different Iranian rice samples.     

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 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.     

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 Squalene, α-Tocopherol and β-Carotene in Table Olives by Solid Phase Extraction and High-Performance Liquid Chromatography with Diode Array Detection

Olives, the fruit of the Olea europaea tree, are highly appreciated in olive oil and table olives (20 % of crops) not only for their flavor but also for their nutritional properties, especially for antioxidant compounds such as squalling (SQ), α-tocopherol (TH) and β-carotene (BC). This paper presents a new analytical method for simultaneously determining SQ, TH and BC in table olives by using solid phase extraction (SPE) and high performance-liquid chromatography with diode array detection (HPLC-DAD), avoiding the classic saponification process. The correlation coefficients of calibration curves of the analyzed compounds ranged from 0.998 to 0.999, and the recoveries were in the range of 89.4–99.6 %. The validated method was used to analyze 30 table olive samples from Italy for their content of SQ (537–1,583 mg kg^?1), TH (21–90 mg kg^?1) and BC (0.4–2.6 mg kg^?1). Finally, experiments with HPLC-MS were conducted to compare this novel method with the classic saponification procedure.     

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.     

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.     

Development of a Dispersive Liquid–Liquid Microextraction Method for the Determination of α-Tocopherol in Pigmented Wheat by High-Performance Liquid Chromatography

A dispersive liquid–liquid microextraction (DLLME) method coupled to high-performance liquid chromatography was developed for the analysis of α-tocopherol in grain samples. The DLLME parameters including the type and volume of extractants, the volume of disperser and the addition of salt were examined. The optimized DLLME procedure consisted in the formation of a cloudy solution promoted by the fast addition to the sample (5 mL of saponified sample solution diluted with 5 mL of water) of a mixture of carbon tetrachloride (extraction solvent, 80 μL) and ethanol (dispersive solvent, 200 μL) without the addition of salt, followed by shaking for 5 min and centrifuging for 3 min at 5,000 rpm. Intra- and inter-day repeatability expressed as % RSD were 3.5 and 7.6 %, respectively. The limit of detection and the limit of quantification were 1.9 and 6.3 μg?L^?1. The comparison of this method with the national standardized extraction method, supercritical carbon dioxide extraction, accelerated solvent extraction, and conventional heat-reflux extraction indicates that the DLLME was accurate (no significant differences at the 0.05 % probability level), high efficient, low organic solvent-consuming, and low cost. This procedure was successfully applied to 42 samples of 14 types of purple wheat, for which the content of α-tocopherol exhibited a significantly negative correlation with the pigment content measured by a spectrophotometer. The recovery rates ranged from 90.5 to 103.7 %.