Comparison of pulse glow discharge‐ion mobility spectrometry and liquid chromatography with tandem mass spectrometry based on multiplug filtration cleanup for the analysis of tricaine mesylate residues in fish and water

Analytical methods based on multiplug filtration cleanup coupled with pulse glow discharge‐ion mobility spectrometry and liquid chromatography tandem mass spectrometry were developed for the analysis of tricaine mesylate residue in fish and fish‐raising water samples. A silica fiber holder and an appropriate new interface were designed to make the direct introduction of the fiber into the pulse glow discharge‐ion mobility spectrometry introduction mechanism. The multiplug filtration cleanup method with adsorption mixtures was optimized for the determination of tricaine mesylate in fish samples. Good linear relationships were obtained by the two methods. For fish samples, limits of detection were 6 and 0.6 μg/kg by ion mobility spectrometry and liquid chromatography with tandem mass spectrometry, respectively. The matrix effect of the established liquid chromatography tandem mass spectrometry method was negligible for fish samples but that of the ion mobility spectrometry method was not. The two methods were compared. The ion mobility spectrometry system could be used a rapid screening tool on site with the advantage of rapidity, simplicity, and portability, and the liquid chromatography tandem mass spectrometry system could be used for validation in laboratory conditions with the advantage of lower limit of detection, stability, and precision.     

Application of multiwalled carbon nanotubes for the preconcentration and determination of organochlorine pesticides in water samples by gas chromatography with mass spectrometry

A fast, sensitive, and convenient technique consisting of a miniaturized solid‐phase extraction method named microextraction in packed syringe coupled with gas chromatography and mass spectrometry was developed for the preconcentration and determination of some pesticides, including hexachlorobenzene, heptachlor, alachlor, aldrine, and metolachlore, in natural water samples. Carboxyl‐purified multiwalled carbon nanotubes were used as a sorbent in microextraction in packed syringe. Based on this technique, 6.0 mg of multiwalled carbon nanotubes was inserted in the syringe between two polypropylene frits. The analytes would be adsorbed on the solid phase, and would subsequently be eluted using organic solvents. The influence of some important parameters involved including the solution pH, type, and volume of the organic desorption solvent, and amount of the multiwalled carbon nanotubes sorbent on the extraction efficiency of the selected pesticides were investigated. The proposed method showed a good linearity in the range of 0.1–25.0 ng/mL and low limits of detection in the range of 0.02–0.19 ng/mL using the selected ion‐monitoring mode. Reproducibility of the method was in the range of 3.3–8.5% for the studied pesticides. Also to evaluate the matrix effect, the developed method was applied to the preconcentration and determination of the selected pesticides in different water samples.     

Analytical method for 44 pesticide residues in spinach using multi‐plug‐filtration cleanup based on multiwalled carbon nanotubes with liquid chromatography and tandem mass spectrometry detection

Spinach is one of the most commonly planted vegetables worldwide. A high chlorophyll content makes spinach a complicated matrix in pesticide residue analysis. In this study, a rapid clean‐up method was developed for the analysis of pesticide multi‐residues in spinach followed by liquid chromatography with tandem mass spectrometry. A modified QuEChERS method with multiwalled carbon nanotubes and carbon material was adopted in the multi‐Plug Filtration Cleanup procedure. This method was validated for 44 representative pesticides spiked at two concentration levels of 10 and 100 μg/kg. The pesticides of different physicochemical properties were registered on spinach in China. The recoveries were between 76 and 114% for major pesticides with relative standard deviations of less than 15%, except for quizalofop‐P‐ethyl, pyrimethanil, and carbendazim. Matrix‐matched calibration curves were performed with the coefficients of determination higher than 0.995 for the studied pesticides for concentration levels of 10–500 μg/kg. The limits of quantitation ranged from 2 to 10 μg/kg. The developed method was successfully applied to determine pesticide residues in Chinese market spinach samples.     

Determination of organophosphorus pesticides by gas chromatography with mass spectrometry using a large‐volume injection technique after magnetic extraction

A fast and efficient method was developed for the extraction and determination of organophosphorus pesticides in water samples. Organophosphorus pesticides were extracted by solid‐phase extraction using magnetic multi‐walled carbon nanotubes and determined by gas chromatography with ion‐trap mass spectrometry. Parameters affecting the extraction were investigated. Under optimum conditions of the method, 10 mg magnetic multi‐walled carbon nanotubes were added into 10 mL sample. After 2 min, adsorbent particles settled at the bottom of test tube with a magnet. After removing aqueous supernatant, the analytes were desorbed with acetonitrile. Then, 70 μL of acetonitrile phase was injected into the gas chromatography and mass spectrometry system that had an ion‐trap analyzer. To achieve high sensitivity, the large‐volume‐injection technique was used with a programmed temperature vaporization inlet, and the ion‐trap mass spectrometer was operated in single ion storage mode. Under the best conditions, the enrichment factors and extraction recoveries were in the range of 113–124 and 74–103%, respectively. The limits of detection were between 3 and 15 ng/L, and the relative standard deviations were < 10%. This method was successfully used for the determination of organophosphorus pesticides in dam water, lagoon water, and river water samples with good reproducibility and recovery.     

Analysis of Malathion pesticide residues in rice samples using ultrasound-assisted emulsification-microextraction coupled to UV photoionization source ion mobility spectrometry

The present paper describes the validation of ultrasound-assisted emulsification-microextraction method followed by ion mobility spectrometry (IMS) for determination malathion pesticides. Ultrasound radiation was applied for accelerating the emulsification of microliter organic solvent in aqueous solutions and enhancing the microextraction efficiency. This preconcentration step combined with IMS detection provided a precise and accurate method for determination of trace amounts of malathion pesticides. The effect of parameters influencing the extraction efficiency such as sonication time, type of extraction solvent, extraction solvent volume, and salt concentration were investigated and discussed. Under the optimum conditions, enrichment factors was 270 with corresponding LOD of 4 μg/L. Linearity with a coefficient of estimation (r²) were >0.99 in the concentration level range of 6–750 μg/L for extraction of Malathion in water samples. The applicability of the proposed method was evaluated by determination of the residues of the investigated pesticide in rice paddy water gathered from four stations during 60 days after spraying (June 2014), and in storage rice samples in Mazandaran province, Iran.     

Rapid multiplug filtration cleanup method for the determination of 124 pesticide residues in rice,wheat, and corn

A simple and rapid multiplug filtration cleanup method based on multiwalled carbon nanotubes was developed to determine 124 pesticide residues in rice, wheat, and corn, which could be done in a few seconds without conditioning and elution steps. Various combinations of sorbents were optimized for each matrix with a dispersive solid‐phase extraction procedure to get a satisfactory recovery and clean‐up performance. Good linearity was obtained for all pesticides with calibration curve coefficients larger than 0.9958. Most recoveries for the majority pesticides were between 70 and 120% (n = 5) with relative standard deviations below 20%. The limit of detection was 0.1–1.3 μg/kg, and the limit of quantification was 0.2–4.3 μg/kg for the pesticides in all matrices. The work suggests that the multiplug filtration cleanup method is better than the dispersive solid‐phase extraction method and it could be applied to routinely monitor pesticide residues in market samples.     

Determination of multi‐pesticide residue in tobacco using multi‐walled carbon nanotubes as a reversed‐dispersive solid‐phase extraction sorbent

A multi‐pesticide residue determination method based on a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method using multiwalled carbon nanotubes as reversed‐dispersive solid‐phase extraction material was validated in 37 representative pesticides in tobacco. Determination was performed using liquid chromatography with tandem mass spectrometry in multiple reaction monitoring mode. Three major types of tobacco leaf samples, namely, flue‐cured, burley, and oriental tobacco were studied and compared. Three factors (extraction time, external diameter, and amount of extraction material used) that could affect the performance of multi‐walled carbon nanotubes were investigated. Optimization of sample preparation and determination allowed recoveries between 70.8 and 114.8% for all 37 pesticides with < 20.0% relative standard deviations at three spiking levels of 20, 50, and 200 μg/kg. The limits of quantification and limits of detection for the 37 pesticides ranged within 0.46–28.57 and 0.14–8.57 μg/kg at a signal‐to‐noise ratio of 10 and 3, respectively.     

Multiresidue analysis of 16 pesticides in jujube using gas chromatography and mass spectrometry with multiwalled carbon nanotubes as a sorbent

Although jujube is a minor crop and very few pesticides are registered on it, the application of pesticides during the growth stage of jujube is inevitable to control the pests or diseases. This situation has led to pesticide misuse. A modified quick, easy, cheap, effective, rugged, and safe method using a novel sorbent, multiwalled carbon nanotubes, as a dispersive solid‐phase extraction sorbent combined with gas chromatography with mass spectrometry, was developed for the determination of 16 pesticides in jujube. Under the optimized conditions, recoveries of 76.7–112.4% were obtained for the target analytes at three spiked concentration levels. The relative standard deviations ranged from 1.2 to 12.3%. Limits of detection and limits of quantification for 16 pesticides ranged from 1 to 10 and 3 to 30 μg/kg, respectively. The residues of chlorpyrifos, hexaconazole, tebuconazole, and cyhalothrin were detected from samples obtained from the market.     

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.     

Preparation of magnetic molecularly imprinted polymer based on multiwalled carbon nanotubes for selective dispersive micro-solid phase extraction of fenitrothion followed by ion mobility spectrometry analysis

A novel molecularly imprinted polymer based on magnetic multiwalled carbon nanotubes was fabricated and applied for selective dispersive micro-solid phase extraction of fenitrothion prior its determination by ion mobility spectrometry. The composite was synthesized using magnetic multiwalled carbon nanotubes as the support. Methacrylic acid was used as the functional monomer, fenitrothion as the template, ethylene glycol dimethacrylate as the cross-linker, and 2,2-azoisobutyronitrile as the initiator. The resultant polymer was characterized by FTIR spectroscopy, X-ray diffraction, field emission scanning electron microscopy, Brunauer–Emmet–Teller analysis, thermogravimetric analysis, and vibrating sample magnetometer techniques. Experimental factors affecting the extraction efficiency such as pH and amount of sorbent were evaluated. Under optimum experimental conditions, the developed method displayed the linear range of 5–220 μg/L with a detection limit of 1.3 μg/L. The intra- and interday relative standard deviations for determination of fenitrothion were 3.6 and 4.7% (n = 6), respectively. Ultimately, the proposed method was used to monitor trace amounts of fenitrothion in fruits, vegetables, and water samples.     

Extraction of methocarbamol from human plasma with a polypyrrole/multiwalled carbon nanotubes composite decorated with magnetic nanoparticles as an adsorbent followed by electrospray ionization ion mobility spectrometry detection†

In this work, a polypyrrole/multiwalled carbon nanotubes composite decorated with Fe₃O₄ nanoparticles was chemically synthesized and applied as a novel adsorbent for the extraction of methocarbamol from human plasma. Electrospray ionization ion mobility spectrometry was used for the determination of the analyte. The properties of the magnetic‐modified adsorbent were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform IR spectroscopy, and X‐ray diffraction. The effects of experimental parameters on the extraction efficiency of the sorbent were investigated. Under the optimized conditions, the linear dynamic range was found to be 2–150 ng/mL with the detection limit of 0.9 ng/mL. The relative standard deviation was 5.3% for three replicate measurements of methocarbamol in plasma sample. The extraction efficiency of the sorbent for the determination of different drugs with various polarities was also compared to that of Fe₃O₄‐polypyrrole and Fe₃O₄‐multiwalled carbon nanotubes sorbents. Finally, the method was used for the determination of methocarbamol in blood samples.     

Solid‐phase extraction disk based on multiwalled carbon nanotubes for the enrichment of targeted pesticides from aqueous samples

A sensitive method for the determination of six varying polarity pesticides (imidacloprid, acetamiprid, carbendazim, simazine, linuron, and tebufenozide) based on a solid‐phase extraction disk with multiwalled nanotubes is proposed.A dispersion of multiwalled nanotubes in a surfactant aqueous solution (Triton X‐100) was used for the preparation of the solid‐phase extraction disk. The effect of surfactant on the functional groups of multiwalled nanotubes was examined by applying temperature‐programmed desorption. It was found that this treatment increased the amount of oxygen groups of treated multiwalled nanotubes comparing with untreated ones. The factors that may influence the adsorption and recovery such as the kind and volume of eluent, volume, flow rate and pH of sample were investigated and optimized. Under the optimized conditions, the maximal enrichment factors for low polar pesticides are ranging from 4000 to 4985 and for more polar are 2250 and 2750. The linear range of calibration curves was 10–500 ng/L with correlation coefficient higher than 0.9960, and the detection limit was 6.2–23.7 ng/L. Finally optimized method was applied for determination trace level of five out of six pesticides in tap and river water samples with good recovery.     

Multiresidue method for the determination of 227 pesticides in hot pepper (Capsicum annuum L.) by liquid chromatography with tandem mass spectrometry†

A high‐throughput, rapid, and efficient modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method with a simple cleanup procedure has been developed for simultaneously determining 227 pesticides in pepper samples by liquid chromatography with tandem mass spectrometry (running time: 10 min). Pesticide residues were extracted/partitioned with an acetonitrile/DisQuE QuEChERS pouch, and the resulting samples were cleaned up with different methods: dispersive solid‐phase extraction with primary secondary amines or multiwalled carbon nanotubes and graphitized carbon solid mini cartridge column. The results indicated that multiwalled carbon nanotubes dispersive sorbents achieved the best recoveries and had less matrix interference. The numbers of pesticides with a recovery in the range of 70–120% were 199 at a spiked level of 40 μg/kg. The correlation coefficients (r²) for 227 pesticides were above 0.99, while the limits of quantitation of pesticides in pepper samples ranged from 0.13 to 13.51 μg/kg (S/N = 10), and the limits of detection ranged from 0.04 to 4.05 μg/kg (S/N = 3). The relative standard deviations of approximately 197 pesticides were below 20% at spiked levels of 40 μg/kg. Based on these results, the proposed method was chosen as the most suitable cleanup procedure for the determination of multiresidue pesticides in pepper samples.     

Comparison of the Enrichment Efficiency of Multiwalled Carbon Nanotubes, C18 Silica, and Activated Carbon as the Adsorbents for the Solid Phase Extraction of Atrazine and Simazine in Water Samples

Multiwalled carbon nanotubes with exceptional merits as SPE adsorbents for enrichment of environmental pollutants have absorbed much attention. The goal of this paper was to make a comparison with it and regular adsorbents such as C18 silica and activated carbon in the extraction capacity of atrazine and simazine. The results indicated that multiwalled carbon nanotubes were very suitable for determination of atrazine and simazine because of an enrichment performance similar to that of C18 silica. In contrast, the spiked recovery of simazine was higher than that of atrazine using multiwalled carbon nanotubes as packing material for SPE. However, reverse results were obtained when the extraction was performed with packing of C18 silica. Moreover, as the extraction of simazine was concerned, multiwalled carbon nanotubes were much better than C18 silica. As for the enrichment of atrazine, C18 silica achieved greater extraction factor than multiwalled carbon nanotubes. Activated carbon did not give the expected extraction efficiency because of its large size and blank volume and less active sites for adsorption. All these experimental results indicated that multiwalled carbon nanotubes could be used as a valuable alternative adsorbent for SPE of atrazine and simazine in many real water samples.     

QuEChERS结合气相色谱-质谱法测定农产品中杀螨剂和拟除虫菊酯农药残留

建立了QuEChERS-改性多壁碳纳米管提取净化,气相色谱-质谱法同时检测农产品中1种杀螨剂和8种拟除虫菊酯农药的分析方法。样品经水浸润后,以乙酸乙酯-正己烷混合溶剂提取,再以适量改性多壁碳纳米管填料净化提取液,净化液以Shimadzu Rtx-1701毛细管色谱柱为分离柱,采用质谱测定和确证,选择离子模式监测,外标法定量。在优化实验条件下,9种农药在0.010~1.0μg/mL范围内具有良好的线性关系,相关系数为0.9840~0.9977,检出限(S/N=3)为2.2~6.2μg/kg。3个加标水平下的平均回收率为76.7%~107%,相对标准偏差为3.1%~9.5%。该方法准确、灵敏度高、操作简单、快速,可满足新会陈皮等农产品中上述9种农药残留同时测定的要求。     

Simultaneous determination of three organophosphorus pesticides in different food commodities by gas chromatography with mass spectrometry

A sensitive and selective gas chromatography with mass spectrometry method was developed for the simultaneous determination of three organophosphorus pesticides, namely, chlorpyrifos, malathion, and diazinon in three different food commodities (milk, apples, and drinking water) employing solid‐phase extraction for sample pretreatment. Pesticide extraction from different sample matrices was carried out on Chromabond C₁₈ cartridges using 3.0 mL of methanol and 3.0 mL of a mixture of dichloromethane/acetonitrile (1:1 v/v) as the eluting solvent. Analysis was carried out by gas chromatography coupled with mass spectrometry using selected‐ion monitoring mode. Good linear relationships were obtained in the range of 0.1–50 μg/L for chlorpyrifos, and 0.05–50 μg/L for both malathion and diazinon pesticides. Good repeatability and recoveries were obtained in the range of 78.54–86.73% for three pesticides under the optimized experimental conditions. The limit of detection ranged from 0.02 to 0.03 μg/L, and the limit of quantification ranged from 0.05 to 0.1 μg/L for all three pesticides. Finally, the developed method was successfully applied for the determination of three targeted pesticides in milk, apples, and drinking water samples each in triplicate. No pesticide was found in apple and milk samples, but chlorpyrifos was found in one drinking water sample below the quantification level.     

Rapid and sensitive detection of the phenoxy acid herbicides in environmental water samples by magnetic solid‐phase extraction combined with liquid chromatography–tandem mass spectrometry

Phenoxy acid herbicides are widely used herbicides that play an important role in improving the yield and quality of crops. However, some research has shown that this kind of herbicide is poisonous to human and animals. In this study, a rapid and sensitive method was developed for the detection of seven phenoxy acid herbicides in water samples based on magnetic solid‐phase extraction followed by liquid chromatography and tandem mass spectrometry. Magnetic amino‐functionalized multiwalled carbon nanotubes were prepared by mixing bare magnetic Fe₃O₄ nanoparticles with commercial amino‐functionalized multiwalled carbon nanotubes in water. Then the amino‐functionalized multiwalled carbon nanotubes were used to enrich phenoxy acid herbicides from water samples based on hydrophobic and ionic interactions. The effects of experimental variables on the extraction efficiency have been studied in detail. Under the optimized conditions, the method validation was performed. Good linearities for seven phenoxy acid herbicides were obtained with squared regression coefficients ranging from 0.9971 to 0.9989. The limits of detection ranged from 0.01 to 0.02 μg/L. The method recoveries of seven phenoxy acid herbicides spiked at three concentration levels in a blank sample were from 92.3 to 103.2%, with inter‐ and intraday relative standard deviations less than 12.6%.     

Evaluation and validation of an ion mobility quadrupole time‐of‐flight mass spectrometry pesticide screening approach

An ion mobility quadrupole time‐of‐flight mass spectrometry‐based pesticide suspect screening methodology was developed and validated covering 20 plant‐derived food matrices deriving from six commodity groups of different complexity according to the actual European Commission document SANTE/11813/2017 applying a QuEChERS sample preparation protocol. The method combines ultra‐performance liquid chromatography, traveling wave ion mobility, and quadrupole time‐of‐flight mass spectrometry. Besides the determination of the physicochemical property collision cross‐section and the establishment of a corresponding scientific suspect screening database comprising 280 pesticides for several pesticides, different protomers, sodium adducts, as well as dimers were identified in ion mobility spectrometry traces. Additionally, collision cross‐section values were included in the validation requirements regarding chromatography and mass spectrometry for the detection of pesticides. A collision cross‐section value window was analyzed within a tolerable error of ±2%. For this cross‐matrix validation, screening detection limits were determined at concentration levels of 0.100 mg/kg (84% of the original pesticide scope), 0.010 mg/kg (56%), and 0.001 mg/kg (21%). By application of ion mobility spectrometry, the compound identification was improved due to independence of commodity of concern and concentration levels of analyte molecules, as false assignments are reduced by application of a collision cross‐section range.     

Liquid extraction surface analysis (LESA) of food surfaces employing chip‐based nano‐electrospray mass spectrometry

An automated surface‐sampling technique called liquid extraction surface analysis (LESA), coupled with infusion nano‐electrospray high‐resolution mass spectrometry and tandem mass spectrometry (MS/MS), is described and applied to the qualitative determination of surface chemical residues resulting from the artificial spraying of selected fresh fruits and vegetables with representative pesticides. Each of the targeted pesticides was readily detected with both high‐resolution and full‐scan collision‐induced dissociation (CID) mass spectra. In the case of simazine and sevin, a mass resolution of 100 000 was insufficient to distinguish the isobaric protonated molecules for these compounds. When the surface of a spinach leaf was analyzed by LESA, trace levels of diazinon were readily detected on the spinach purchased directly from a supermarket before they were sprayed with the five‐pesticide mixture. A 30 s rinse under hot running tap water appeared to quantitatively remove all remaining residues of this pesticide. Diazinon was readily detected by LESA analysis on the skin of the artificially sprayed spinach. Finally, incurred pyrimethanil at a level of 169 ppb in a batch slurry of homogenized apples was analyzed by LESA and this pesticide was readily detected by both high‐resolution mass spectrometry and full‐scan CID mass spectrometry, thus showing that pesticides may also be detected in whole fruit homogenized samples. This report shows that representative pesticides on fruit and vegetable surfaces present at levels 20‐fold below generally allowed EPA tolerance levels are readily detected and confirmed by the title technologies making LESA‐MS as interesting screening method for food safety purposes. Copyright © 2011 John Wiley & Sons, Ltd.