A sol‐gel based solid phase microextraction fiber for the analysis of aliphatic alcohols in apple juices

A new fiber based on titania‐chitin sol‐gel coated on a silver wire for the headspace solid phase microextraction of aliphatic alcohols from apple juice samples was developed. The influences of fiber coating composition and microextraction conditions (extraction temperature, extraction time, and ionic strength of the sample matrix) on the fiber performance were investigated. Also, the influence of temperature and time on desorption of analytes from fiber were studied. Under the optimized conditions, a porous fiber with a high extraction capacity and good thermal stability (up to 250°C) was obtained. The proposed headspace solid‐phase microextraction‐GC method was successfully used for the analysis of aliphatic alcohols in apple juice and concentrate samples. The recovery values were from 92.8 to 98.6%. The RSD (n=5) for all analytes were below 7.8%.     

Graphene‐based pipette tip solid‐phase extraction with ultra‐high performance liquid chromatography and tandem mass spectrometry for the analysis of carbamate pesticide residues in fruit juice

Graphene‐based pipette tip solid‐phase extraction was combined with ultra‐high performance liquid chromatography and tandem mass spectrometry for the determination of carbamate pesticide residues in fruit juice samples. Four milligrams of graphene was used as sorbent material to pack a 1000 μL pipette tip for the extraction of pirimicarb, propoxur, isoprocarb, fenobucarb, and diethofencarb from 3 mL of fruit juice sample. The whole extraction process was finished in 12 min, and the volume of eluent used was only 1.5 mL. Under the optimized conditions, good linear relationship (R > 0.999) and lower limits of detection (0.0022–0.033 ng/mL) were achieved. The recoveries at three spiked levels ranged from 80.90 to 124.60% with relative standard deviations less than 4.88%. Compared with commercially available sorbents including propylsulfonic acid silica, graphitized carbon black, and C₁₈, graphene was superior in extraction efficiency. The proposed method is simple, rapid, sensitive, selective, and solvent saving.     

Binary–solvent–based ionic–liquid–assisted surfactant‐enhanced emulsification microextraction for the determination of four fungicides in apple juice and apple vinegar

A binary–solvent–based ionic–liquid–assisted surfactant‐enhanced emulsification microextraction method was developed for the separation/preconcentration and determination of four fungicides (pyrimethanil, fludioxonil, cyprodynil, pyraclostrobin) in apple juice and apple vinegar. A nonchlorinated solvent amyl acetate, which has a lower density than water, was used as the extraction solvent, and an ionic liquid 1‐hexyl‐3‐methylimidazolium hexafluorophosphate, which has a high density and low toxicity, was used as a secondary solvent mixed with the extraction solvent. After centrifugation, the binary solvent drop with a relatively high density was deposited on the bottom of the tube. Some parameters influencing the extraction efficiency of analytes such as type of extraction solvent, ratio of ionic liquid, volume of mixed solvent, type and concentration of surfactant, sample pH, NaCl concentration, and vortex time were investigated and optimized. Under the optimized conditions, the proposed method provided a good linearity in the range of 5–200 μg/L. The limits of quantification of the method were in the range of 2–5 μg/L. The relative standard deviations for interday assays were 1.7–11.9%. The method was applied to the determination of pyrimethanil, fludioxonil, cyprodynil, and pyraclostrobin in apple juice and apple vinegar samples, and the accuracy was evaluated through recovery experiments.     

Multiplug filtration clean‐up with multiwalled carbon nanotubes in the analysis of pesticide residues using LC–ESI‐MS/MS

A novel design for a rapid clean‐up method was developed for the analysis of pesticide residues in fruit and vegetables followed by LC–ESI‐MS/MS. The acetonitrile‐based sample extraction technique was used to obtain the extracts, and further clean‐up was carried out by applying the streamlined procedure on a multiplug filtration clean‐up column coupled with a syringe. The sorbent used for clean‐up in this research is multiwalled carbon nanotubes, which was mixed with anhydrous magnesium sulfate to remove water from the extracts. This method was validated on 40 representative pesticides and apple, cabbage, and potato sample matrices spiked at two concentration levels of 10 and 100 μg/kg. It exhibited recoveries between 71 and 117% for most pesticides with RSDs < 15%. Matrix‐matched calibrations were performed with the coefficients of determination >0.995 for most studied pesticides between concentration levels of 10–500 μg/L. The LOQs for 40 pesticides ranged from 2 to 50 μg/kg. The developed method was successfully applied to the determination of pesticide residues in market fruit and vegetable samples.     

Dispersive solid‐phase extraction for the determination of trace organochlorine pesticides in apple juices using reduced graphene oxide coated with ZnO nanocomposites as sorbent

In this work, reduced graphene oxide coated with ZnO nanocomposites was used as an efficient sorbent of dispersive solid‐phase extraction and successfully applied for the extraction of organochlorine pesticides from apple juice followed by gas chromatography with mass spectrometry. Several experimental parameters affecting the extraction efficiencies, including the amount of adsorbent, extraction time, and the pH of the sample solution, as well as the type and volume of eluent solvent, were investigated and optimized. Under the optimal experimental conditions, good linearity existed in the range of 1.0–200.0 ng/mL for all the analytes with the correlation coefficients (R ²) ranging from 0.9964 to 0.9994. The limits of detection of the method for the compounds were 0.011–0.053 ng/mL. Good reproducibilities were acquired with relative standard deviations below 8.7% for both intraday and interday precision. The recoveries of the method were in the range of 78.1–105.8% with relative standard deviations of 3.3–6.9%.     

Use of graphene coated with ZnO nanocomposites for microextraction in packed syringe of carbamate pesticides from juice samples

In this work, nanocomposites of reduced graphene oxide coated with ZnO were synthesized using a hydrothermal reduction strategy. Nanocomposite was then used as a sorbent for microextraction in a packed syringe, and its application to the extraction of carbamate pesticides from juice samples prior to high‐performance liquid chromatography detection was demonstrated. Factors affecting the enrichment efficiency of the microextraction in a packed syringe procedure were optimized, which included desorption conditions, sample pH, salting‐out effect, washing solution, and sample cycles. Under optimal conditions, the prepared materials exhibited excellent enrichment efficiency for carbamate pesticides. Good linearity existed in the concentration range of 0.5–200 ng/mL, with correlation coefficients of 0.9991–0.9997. The limits of detection of these carbamate pesticides were in the range of 0.23–1.21 ng/mL, and the average recoveries of the analytes at two spiked levels for real‐sample analysis ranged from 90.5 to 104.2% with relative standard deviations of 3.6–5.9%.     

Graphene as an efficient sorbent for the SPE of organochlorine pesticides in water samples coupled with GC–MS

The determination of organochlorine pesticides in water samples, which are harmful to humans, is very important for environmental risk assessment. Based on the excellent adsorption properties of graphene, an SPE coupled with GC–MS method for the monitoring of organochlorines (four hexachlorcyclohexanes and four dichlorodiphenyltrichloroethanes) was developed. Owing to the hydrophobic interaction and π–π stacking interaction between the analytes and graphene, the analytes quantitatively adsorbed onto the graphene‐based SPE cartridge were eluted by ethyl acetate for analysis. Several parameters influencing the analytical performance, such as the kind of elution, sample volume, reusability of the cartridge, have been investigated in detail. Under the optimal conditions, detection of limits of 1.95–9.38 ng/L, recoveries of 83.9–107.3% at two spiked concentration levels (0.1 and 10 ng/mL) and RSDs in the range of 2.9–7.4% for real water samples were obtained for all the analytes. This work reveals the great potential of graphene in sample preparation procedures.     

Graphene‐based solid‐phase extraction disk for fast separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples

Graphene has great potentials for the use in sample preparation due to its ultra high specific surface area, superior chemical stability, and excellent thermal stability. In our work, a novel graphene‐based SPE disk was developed for separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples. Based on the strong π–π stacking interaction between the analytes and graphene, the analytes extracted by graphene were eluted by cyclohexane and then determined by GC‐MS. Under the optimized conditions, high flow rate (30 mL/min) and sensitivity (0.84–13 ng/L) were achieved. The proposed method was successfully applied to the analysis of real environmental water samples with recoveries ranging from 72.8 to 106.2%. Furthermore, the property of anticlogging and reusability was also improved. This work reveals great potentials of graphene‐based SPE disk in environmental analytical.     

Determination of chloramphenicol in aquatic products by graphene‐based SPE coupled with HPLC‐MS/MS

An effective analytical protocol using graphene‐based SPE coupled with HPLC‐MS/MS for determination of chloramphenicol (CAP) in aquatic products has been developed. In the present work, graphene was evaluated as SPE sorbents for the analytes enrichment and clean up. The target analytes were quantified by a triple‐quadrupole linear ion trap MS in multiple‐reaction monitoring mode. In addition, the proposed method was validated according to Commission Decision 2002/657/EC. The calibration curve was linear over the range of 0.5–100 ng/mL. The mean values of RSD of intra‐ and interday ranging from 1.48 to 4.29% and from 3.25 to 7.42% were obtained, respectively. In the three fortified levels, the recoveries of CAP ranging from 92.3 to 103.4% with RSDs ≤ 5.58% were obtained. The proposed method has been successfully applied to the analysis of CAP in several aquatic product samples, indicating that graphene was a potential SPE sorbent for the enrichment of trace residues in food samples.     

Phytic acid induced three‐dimensional graphene for the enrichment of phthalate esters from bottled water and sports beverage samples

A three‐dimensional graphene was synthesized through a hydrothermal reaction of graphene oxide with phytic acid. The microstructure and morphology of the phytic acid induced three‐dimensional graphene were investigated by nitrogen adsorption–desorption isotherms, scanning electron microscopy, and transmission electron microscopy. With a large surface area and three‐dimensional structure, the graphene was used as the solid‐phase extraction adsorbent for the extraction of phthalate esters from bottled water and sports beverage samples before high‐performance liquid chromatographic analysis. The results indicated that the graphene was efficient for the solid‐phase extraction of phthalate esters. The limits of detection (S/N = 3) of the method for the analytes were 0.02–0.03 ng/mL for the water samples and 0.03–0.15 ng/mL for the sports beverage sample. The limits of quantitation (S/N = 9) for the analytes were 0.06–0.09 ng/mL for water samples and 0.09–0.45 ng/mL for sports beverage sample. The calibration curves for the phthalate esters by the method had a good linearity from 0.1 to 80.0 ng/mL with correlation coefficients larger than 0.9997. The recoveries of the analytes for the method fell in the range of 86.7–116.2% with the relative standard deviations between 1.5 and 6.8%.     

Magnetic octadecyl‐based matrix solid‐phase dispersion coupled with gas chromatography with mass spectrometry in a proof‐of‐concept determination of multi‐class pesticide residues in carrots

A novel procedure is put forward based on the combination of the well‐established matrix solid‐phase dispersion and the magnetic and sorption properties of magnetic octadecyl in the presence of n‐octanol and was employed in a proof‐of‐concept sample preparation and determination of several classes of pesticide residues in carrots. The procedure does not require the transfer of blend to cartridge and subsequent packing, nor any co‐sorbent for extract clean up. The hydrophobic magnetic nanoparticles utilized as a sorbent, can be retrieved by n‐octanol under the application of a magnetic field due to hydrophobic interactions. Elution of pesticide residues is then carried out with an organic solvent. A total of 26 pesticides were included in this procedure and the target compounds were analyzed using gas chromatography with mass spectrometry in the selective ion monitoring mode. The average extraction recoveries obtained from carrot samples fortified at three different concentrations (20, 50, and 500 μg/kg) were 77–107%. The estimated limits of quantitation for most target analytes were in the low μg/kg level. The study demonstrates that the proposed extraction procedure is simple and effective, avoiding a clean‐up step for the sample preparation of vegetable.     

Effervescence‐assisted dispersive liquid–liquid microextraction using a solid effervescent agent as a novel dispersion technique for the analysis of fungicides in apple juice

A novel effervescence‐assisted dispersive liquid–liquid microextraction method has been developed for the determination of four fungicides in apple juice samples. In this method, a solid effervescent agent is added into samples to assist the dispersion of extraction solvent. The effervescent agent is environmentally friendly and only produces an increase in the ionic strength and a negligible variation in the pH value of the aqueous sample, which does not interfere with the extraction of the analytes. The parameters affecting the extraction efficiency were investigated including the composition of effervescent agent, effervescent agent amount, formulation of effervescent agent, adding mode of effervescent agent, type and volume of extraction solvent, and pH. Under optimized conditions, the method showed a good linearity within the range of 0.05–2 mg/L for pyrimethanil, fludioxonil, and cyprodinil, and 0.1–4 mg/L for kresoxim‐methyl, with the correlation coefficients >0.998. The limits of detection for the method ranged between 0.005 and 0.01 mg/L. The recoveries of the target fungicides in apple juice samples were in the range of 72.4–110.8% with the relative standard deviations ranging from 1.2 to 6.8%.     

Simultaneous determination of 103 pesticide residues in tea samples by LC‐MS/MS

A simple and sensitive method was developed and validated for the simultaneous determination of 103 pesticide residues in tea by LC‐MS/MS. For the analysis of the pesticide with polarity, thermal lability or low volatility, this LC‐MS/MS method has an advantage over GC. In this work, residual pesticides were extracted from the tea sample with ACN and then purified using Carb‐NH₂ SPE cartridges. Using the multiple reaction monitoring mode, the pesticides were quantified and identified by the most abundant and characteristic fragment ions. The recoveries obtained for each pesticide ranged between 65 and 114% at three spiked concentration levels. The intra‐day precisions were lower than 19.6%. Good linear relationships were observed with the correlation coefficients r² >0.996 for all analytes. The established method was successfully applied to the determination of pesticide residues in real tea samples.     

Fabrication of boron‐rich multiple monolithic fibers for the solid‐phase microextraction of carbamate pesticide residues in complex samples

To enrich carbamate pesticides from complex matrices, an adsorbent based on poly (vinylboronic anhydride pyridine complex‐co‐ethylenedimethacrylate) monolith was fabricated and utilized as the extraction phase of multiple monolithic fiber solid‐phase microextraction. Due to the abundant boron atoms in the monolith, the B–N coordination interaction between adsorbent and analytes play a key role in the efficient extraction of analytes. Under the optimized conditions, the monolithic fibers were combined with high‐performance liquid chromatography for the quantify trace levels of carbamate pesticides in environmental water and orange juice samples. For water sample, the limit of detection and limit of quantification were in the range of 0.017–0.29 and 0.057–0.96 μg/L, respectively. The related values in orange juice samples were 0.038–0.39 and 0.12–1.36 μg/kg, respectively. Besides, the proposed method also exhibits wide linearity, satisfactory coefficients of determination, and good precision. The introduced approach was successfully applied to determine trace target analytes in real‐life samples. The spiked recoveries with different fortified concentrations were in the range of 80.4–117% for water samples and 83.7–119% for fruit juice samples. The relative standard deviations were below 10%. The results evidence that the suggested method was convenient, reliable, and eco‐friendly for the monitoring of trace levels of carbamate pesticides in complex samples such as waters and juices.     

Determination of multiclass pesticide residues in apple juice by gas chromatography-mass spectrometry with large-volume injection

This study presents two GC-MS SIM methods, in combination with large-volume injection programmed-temperature vaporization (LVI-PTV) injection, for the determination of 141 pesticide residues in apple juice. The sample was extracted with ACN, and coextractives were removed with primary/secondary amine sorbent. ACN extract (20 microL) was injected into a PTV injection port in solvent vent mode, and the pesticides were determined by GC-MS using retention time locking software. Deuterium-labeled pesticides (surrogate standards) were used for analytical quality control. In the validation experiments, pesticides recoveries were found to be 70-121% with RSDs of 4.6-21% (n = 6).     

Determining multi‐pesticide residues in teas by dispersive solid‐phase extraction combined with speed‐regulated directly suspended droplet microextraction followed by gas chromatography–tandem mass spectrometry

In this study, an effective speed‐regulated directly suspended droplet microextraction method was developed to condense pesticide residues from teas through dispersive solid‐phase extraction prior to analysis by gas chromatography with tandem mass spectrometry. The extractant was intentionally dispersed into the sample solution in the form of globules through high‐speed agitation. This procedure increases the contact area between the binary phases and shortens the distribution equilibrium time. The fine globules reassembled by decelerating stirring speed, the extractant could be taken out for gas chromatography with tandem mass spectrometry. Recovery studies were performed under optimized extraction conditions by using matrix blanks fortified with pesticides at three concentrations (10, 50, and 100 µg/kg). Over 87% of the recoveries for the analytes in four tea matrices were acceptable given their recovery ranges of 70–120% and relative standard deviations of ≤20%. The limits of quantification of most pesticides were lower than 10 µg/kg and thus satisfied the requirements for maximum residue levels prescribed by the European Community. A total of 38 tea samples from local markets were analyzed by using the proposed method. Results showed that chlorpyrifos was the most frequently detected pesticide in teas. The method is a potential choice for the routine monitoring of pesticide residues in complex matrices.     

基于氧化石墨烯气凝胶固相萃取柱检测有机磷农药北大核心CSCD

以氧化石墨烯气凝胶三维纳米材料作为固相萃取的吸附剂,结合高效液相色谱,对食品中的有机磷农药(辛硫磷、双硫磷、倍硫磷、杀螟硫磷)进行检测分析。首先,利用冷冻干燥的方式制备得到氧化石墨烯气凝胶,通过扫描电镜、红外光谱、比表面积吸附等一系列的实验手段对其形貌及物理特性进行了表征,证明其成功合成。从扫描电镜中可见石墨烯的层状褶皱结构,其表面积为740.51 m^(2)/g。然后,将氧化石墨烯气凝胶直接填充于固相萃取柱中,在未借助任何硅胶等基体的条件下进行萃取研究;通过单因素实验,系统研究了萃取和洗脱条件对有机磷农药萃取回收率的影响。结果显示,在上样体积15 mL、样品溶液pH值4、上样速率1.0 mL/min、洗脱剂1.0 mL乙腈的条件下萃取回收率最高。与商用的萃取材料进行比较,包括碳十八硅胶柱(C18)、阴离子交换柱(SAX)、氨基柱(-NH_(2))和硅酸镁柱(Florisil),氧化石墨烯气凝胶填充的固相萃取柱的萃取回收率有明显提高。实验考察了氧化石墨烯气凝胶直接填充的萃取柱的寿命,结果显示该萃取柱可以重复使用15次,可见解决了分散无基体支撑的石墨烯纳米片容易破碎、堵塞筛板的问题。与液相色谱联用建立分析方法,4种有机磷农药的线性范围较宽,辛硫磷、双硫磷和倍硫磷的线性范围为1~200μg/L,杀螟硫磷的线性范围为2~200μg/L,线性拟合良好(线性相关系数r^(2)≥0.9949),检出限为0.2~0.5μg/L,满足于我国和其他国家限定标准的检测。将该方法应用于实际样品,在苹果皮中未检测到有机磷农药,对其进行加标,回收率为70.5%~93.6%,相对标准偏差≤10.4%。     

Development of ultrasound-assisted emulsification microextraction for the determination of seven pesticides in apple juice by gas chromatography–mass spectrometry

Α simple, relatively rapid, sensitive and cost-effective method based on ultrasound-assisted emulsification microextraction (USAEME) followed by gas chromatography coupled with mass spectrometry has been developed for the determination of seven endocrine disruptor pesticides (chlorpyrifos, deltamethrin, dimethoate, fenitrothion, malathion, pendimethalin and procymidone) in apple juice. This approach is based on the emulsification of organic extraction solvent in a diluted apple juice sample by ultrasound radiation and further separation of both liquids phases by centrifugation. The influence of the different parameters affecting the procedure (extraction solvent, extraction solvent volume, ultrasound time, centrifugation time, ionic strength and pH) was evaluated in order to optimise the efficiency of the extraction process. Target analytes were extracted from a 0.5 g apple juice sample that was diluted by 10 times with aqueous buffer solution (pH 7). The optimised USAEME procedure used 100 μL of chloroform as extraction solvent, 8 min of ultrasound extraction, ionic strength (2.5% w/v) and 7.5 min of centrifugation at 3800 rpm. The optimised method presented recoveries between 70 and 113% for the target analytes. Acceptable linearity for all target analytes was recorded with correlation coefficients (r) higher than 0.992. The limits of quantification were found between 1.1 and 4.6 μg kg^?1 ensuring compliance with the maximum residue limits established by the European Commission. The proposed method was applied for the determination of the endocrine disruptor pesticides in apple samples proving its suitability to the Commission Implementing Regulation (EU) no. 400/2014.     

Deep eutectic solvent based gas‐assisted dispersive liquid‐phase microextraction combined with gas chromatography and flame ionization detection for the determination of some pesticide residues in fruit and vegetable samples

In this study, a gas‐assisted dispersive liquid‐phase microextraction method using a deep eutectic solvent as the extraction solvent combined with gas chromatography and flame ionization detection was developed for the extraction and determination of some pesticide residues in vegetable and fruit juice samples. In this method, choline chloride and 4‐chlorophenol at a molar ratio of 1:2 were mixed. By heating and vortexing, a clear, water‐immiscible, and homogeneous liquid was formed. The obtained deep eutectic solvent was added to an aqueous solution of the analytes in a conical test tube. Air was bubbled into the aqueous solution and a cloudy solution was obtained. During this step, the analytes were extracted into the fine droplets of the extraction solvent. After centrifugation, an aliquot of the settled phase was injected into the separation system. Under the optimum extraction conditions, enrichment factors, and extraction recoveries were obtained in the ranges of 247–355 and 49–71%, respectively. The obtained values for the limits of detection and quantification were in the ranges of 0.24–1.4 and 0.71–4.2 μg/L, respectively. The proposed method is simple, fast, efficient, and inexpensive.     

Effect of background derivatization on the signal enhancement of pesticide residues extracted from edible oils

The effect of background derivatization on the signal enhancement of pesticide residues extracted from edible oil samples was studied by GC with negative chemical ionization MS. The analytes were extracted by a solvent extraction process, and the extract was subjected to rapid low‐temperature fat precipitation. The residual fatty acids were silylated by derivatization with N,O‐bis(trimethylsilyl)trifluoroacetamide. The chromatograms obtained from the derivatized samples showed higher signal intensity and lower detection levels when compared to the direct analysis without derivatization. The sensitivity levels of the method are either better or comparable to that of previously reported methodologies. The LODs of the analyzed organochlorine, organophosphorus, and synthetic pyrethroid residues in sunflower, rice bran, and ground oil samples were in the range of 0.02–0.5 ng/g, and the LOQs were in the range of 0.1–2 ng/g. The intraday and interday accuracies were in the range of 81–116% with RSDs less than 14%. The recoveries obtained were in the range of 53–89% with the RSD values less than 13% for all the studied pesticide residues.