Comparison of liquid chromatography using triple quadrupole and quadrupole ion trap mass analyzers to determine pesticide residues in oranges

Determination of the Dissipation Dynamics and Terminal Residue of Bupirimate and Its Metabolites in Cucumber by QuEChERS-Based UPLC-MS/MS

Bupirimate is widely used as a highly active systemic fungicide. However, the frequent and heavy use of bupirimate has led to pesticide residues in crops that threaten human health and food safety. At present, there is limited research on the detection of ethirimol, which is the metabolite of bupirimate. This study established an ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to simultaneously detect bupirimate and ethirimol residues based on QuEChERS pretreatment. The average recoveries of bupirimate and ethirimol in cucumber were between 95.2 and 98.7%, respectively, with relative standard deviations (RSDs) of 0.92-5.54% at fortified levels of 0.01, 0.1, and 5 mg L^-1. The established method was used to determine the residues in field trials in 12 regions of China, and the final residues of bupirimate were all less than the maximum residue limit (MRL). Since the risk quotient (RQ) of bupirimate and ethirimol in cucumber was less than 1.3%, the dietary risk assessment indicated that bupirimate and ethirimol had a low long-term dietary risk to the general population in China. This study provides effective guidance on the proper use of bupirimate in cucumber fields and a reference for establishing the MRL of bupirimate in China.

Τemporal Variation in Pesticide Residues in Citrus Fruits from Chios, Greece, before and after the Development of an Integrated Pest Management Strategy (IPMS): A Five-Year Study (LIFE13 ENV GR/000414)

The temporal variation in pesticide residues in Kampos, of Chios Island, in Greece, was determined between June 2014 and October 2019. Monitoring of residues took place before and after the development of an Integrated Pest Management Strategy (IPMS) for the sustainable control of the Mediterranean fruit fly (medfly) based on mass trapping with the non-toxic and environmentally friendly attractant Biodelear. A total of 1252 samples of citrus fruits, collected from 12 experimental citrus orchards, were analyzed for the presence of 353 active substances and metabolites of pesticides. A modified QuEChERS method and sensitive chromatographic techniques were used. During preparatory monitoring for the project, the most frequently detected pesticides were the insecticides chlorpyrifos, deltamethrin and spirotetramat; the fungicides propamocarb, dimethomorph and mepanipyrim; and the synergist piperonyl butoxide. The implementation of the IPMS to address medfly resulted in a dramatic reduction in the pesticides detected in citrus fruits during confirmatory monitoring, with no detectable residues—which may cause serious problems to human health—in any of the samples analyzed at the end of the project, thus enhancing consumer safety.

Review on in vivo profiling of drug metabolites with LC-MS/MS in the past decade

Metabolite profiling is an indispensable part of drug discovery and development, enabling a comprehensive understanding of the drug's metabolic behavior. Liquid chromatography-mass spectrometry facilitates metabolite profiling by reducing sample complexity and providing high sensitivity. This review discusses the in vivo metabolite profiling involving LC-MS/MS and the utilization of QTOF, QQQ mass analyzers with a particular emphasis on a mass filter. Further, a summary of sample extraction procedures in biological matrices such as plasma, urine, feces, serum and hair as in vivo samples are outlined. toward the end, we present 15 case studies in biological matrices and their LC-MS/MS conditions to understand the metabolic disposition.

Assessment of field re-entry exposure to pesticides: A dislodgeable foliar residue study

A dislodgeable foliar residue study was conducted in greenhouse pepper and tomato on the island of Crete, Greece, following the spray application of an SC insecticide (with active substance (a.s.) tebufenozide) and an EC fungicide (a.s. bupirimate). Furthermore, for the assessment of worker exposure to pesticides - as a result of re-entering the treated crops - a worker dermal exposure study was carried out during the tasks of tying or pruning, which allowed the transfer coefficient values for the specific tasks to be determined. Pesticide residues were analysed with an in house developed and fully validated HPLC-ESI/MS analytical method. The results from the study resulted in transfer coefficient values which were in agreement with current EFSA guideline values in most of the cases with the exception of bupirimate in a tomato greenhouse. In that case, high potential dermal exposure and low dislodgeable foliar residue values were observed, which is thought to be due to the moist leaves collected during sampling and monitoring, which led to greater than expected transfer coefficient values.

Behaviour of mesotrione in maize and soil system and its influence on soil dehydrogenase activity

The aim of this study was to investigate the dissipation of mesotrione and effect on dehydrogenase activity (DHA) in maize and soil system. The paper for the first time describes behaviour of this herbicide applied at various doses (separately or in mixture with other herbicide) in acidic and alkaline environment. The experiments were conducted using the method randomized blocks in four repetition cycles. Chemical application in seven variants at recommended doses of herbicide were performed. The sample preparation was performed by a modified QuEChERS method and the concentrations of mesotrione in maize and soil were determined by the liquid chromatography with tandem mass spectrometry (LC-MS/MS). The limit of detection was 0.0005mgkg(-1) and quantification 0.001mgkg(-1). The dissipation of mesotrione were described according to first-order (FO) kinetics equation with R(2) were between 0.8794 and 0.9934. The initial deposit of herbicide in soil and maize was higher in an acidic environment (0.06-0.18mgkg(-1)). A positive correlation between an alkaline pH and the rate of dissipation in soil was observed. The results showed that the time after which 50% (DT50) of substance has been degraded was different for both plant and soil. DT50 for soil was within the range 3.2-6.0days and 2.9-4.4days, for the maize 3.9-4.8days and 3.4-4.5days in an alkaline and an acidic environment, respectively. Concentration of mesotrione at applicable MRL level of 0.05mgkg(-1) in maize was achieved at 0.5-5.9days and at proposed MRL of 0.01mgkg(-1) at 8.8-15.8days. The results indicate that the application of mesotrione affected on DHA in the soil. One day after application this herbicide, concentration of DHA in soil was lower than in control plots, but after 21days was observed trend of increasing DHA.

Residual determination and risk assessment of buprofezin in plum (Prunus domestica) grown in open-field conditions following the application of three different formulations

This study was conducted to characterize the residual level and perform a risk assessment on buprofezin formulated as an emulsifiable concentrate, wettable powder, and suspension concentrate over various treatment schedules in plum (Prunus domestica). The samples were extracted with an AOAC quick, easy, cheap, effective, rugged, and safe, 'QuEChERS', method after major modifications. As intrinsic interferences were observed in blank plum samples following dispersive-solid phase extraction (consisting of primary secondary amine and C₁₈ sorbents), amino cartridges were used for solid-phase extraction. Analysis was carried out using liquid chromatography with diode array detection and confirmed by liquid chromatography-tandem mass spectrometry. The method showed excellent linearity with determination coefficient (R²  = 1) and satisfactory recoveries (at two spiking levels, 0.5 and 2.5 mg/kg) between 90.98 and 94.74% with relative standard deviation (RSD) ≤8%. The limit of quantification (0.05 mg/kg) was considerably lower than the maximum residue limit (2 mg/kg) set by the Codex Alimentarius. Absolute residue levels for emulsifiable concentrates were highest, perhaps owing to the dilution rate and adjuvant. Notably, all formulation residues were lower than the maximum residue limit, and safety data proved that the fruits are safe for consumers. Copyright © 2016 John Wiley & Sons, Ltd.

Characterization of the ultraviolet-visible photoproducts of thiophanate-methyl using high performance liquid chromatography coupled with high resolution tandem mass spectrometry-Detection in grapes and tomatoes

UV-visible irradiation of thiophanate-methyl (TM) led to the formation of nine photoproducts that were characterized by high performance liquid chromatography coupled with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Although carbendazime has been reported in the literature to be the major metabolite and photoproduct of thiophanate-methyl, it was not detected in this study. However, an isomer of carbendazime referred as PP2, which was unambiguously characterized owing to CID experiments, was found in great abundance. Grape berries and cherry tomatoes treated with aqueous solutions of thiophanate-methyl were submitted to irradiation under laboratory conditions. TM and PP2 were detected in both peel and flesh of berries. The ability of TM and PP2 to pass through the fruit skin has been shown to be highly compound and matrix dependent. In vitro bioassays on Vibrio fischeri bacteria showed that the global ecotoxicity of the TM solution increases significantly with the irradiation time. PP2 should likely contribute to this ecotoxicity enhancement since in silico estimations for Daphnia magna provide a LC50 value seven times lower for PP2 than for the parent molecule.

A microelectromechanical systems-enabled, miniature triple quadrupole mass spectrometer

Miniaturized mass spectrometers are becoming increasingly capable, enabling the development of many novel field and laboratory applications. However, to date, triple quadrupole tandem mass spectrometers, the workhorses of quantitative analysis, have not been significantly reduced in size. Here, the basis of a field-deployable triple quadrupole is described. The key development is a highly miniaturized ion optical assembly in which a sequence of six microengineered components is employed to generate ions at atmospheric pressure, provide a vacuum interface, effect ion guiding, and perform fragmentation and mass analysis. Despite its small dimensions, the collision cell efficiently fragments precursor ions and yields product ion spectra that are very similar to those recorded using conventional instruments. The miniature triple quadrupole has been used to detect thiabendazole, a common pesticide, in apples at a level of 10 ng/g.

Targeted protein identification, quantification and reporting for high-resolution nanoflow targeted peptide monitoring

Mass spectrometry-based targeted proteomic assays are experiencing a surge in awareness due to the diverse possibilities arising from the re-application of traditional LC-SRM technology. The FDA-approved quantitative LC-SRM-pipeline in drug discovery motivates the use to quantitatively validate putative proteomic biomarkers. However, complexity of biological specimens bears a huge challenge to identify, in parallel, specific peptides and proteins of interest from large biomarker candidate lists. Methods have been devised to increase scan speeds, improve detection specificity and verify quantitative SRM-features. In contrast, high-resolution mass spectrometers could be used to improve reliability and precision of targeted proteomics assays. Here, we present a new method for identifying, quantifying and reporting peptides in high-resolution targeted proteomics experiments performed on an orbitrap hybrid instrument using stable isotope-labeled internal reference peptides. This high precision targeted peptide monitoring (TPM) method has unique advantages over existing techniques, including the need to only detect the most abundant product ion of a given target for confident peptide identification using a scoring function that evaluates assay performance based on 1) m/z-mass accuracy, 2) retention time accuracy of observed species relative to prediction, and 3) retention time accuracy relative to internal reference peptides. Further, we show management of multiplexed precision TPM-assays using sentinel peptide standards. This article is part of a Special Issue entitled: From protein structures to clinical applications.

Quantification of ionophores in aged poultry litter using liquid chromatography tandem mass spectrometry

Veterinary anticoccidials, biochemically known as ionophores, are widely used in poultry feed at therapeutic levels to treat Coccidiosis and at sub-therapeutic levels for growth- promotion. Commonly used ionophores in the US poultry industry are monensin, salinomycin, lasalocid and narasin. There is an increasing concern regarding the persistence of these anticoccidials in the environment. However, little attention has been directed to methods development for quantitatively measuring ionophores in complex environmental matrices such as poultry litters that are land applied. Here, we describe a rapid and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS)-based method developed for simultaneous quantification of monensin, lasalocid, salinomycin, and narasin in aged poultry litter samples. Results show significant level of monensin (97.8 ± 3.2 μg kg⁻¹), lasalocid (19.2 ± 6.6 μg kg⁻¹), salinomycin (70 ± 2.7 μg kg⁻¹) and narasin (57.3 ± 2.6 μg kg⁻¹) in poultry litter stored for over three years at < 5°C. Our findings indicate that even after several years of unmanaged storage of poultry litter, ionophores may continue to persist in this matrix, raising the possibility of prolonged release into the environment.

Advantages of the scheduled selected reaction monitoring algorithm in liquid chromatography/electrospray ionization tandem mass spectrometry multi-residue analysis of 242 pesticides: a comparative approach with classical selected reaction monitoring mode

This paper illustrates the advantages of using the scheduled selected reaction monitoring (sSRM) algorithm available in Analyst Software 1.5 to build SRM acquisition methods in the application field of pesticide multi-residue analysis. The principle is to monitor the SRM transitions only when necessary. Based on the analytes' retention times, the scheduled SRM algorithm decreases the number of concurrent SRM transitions monitored at any point in time, allowing both cycle time and dwell time to remain optimal at higher levels of SRM multiplexing. To compare the scheduled SRM and the classical SRM modes, a mixture containing 242 multi-class pesticides has been analyzed ten times by three acquisition methods, using liquid chromatography/tandem mass spectrometry (LC/MS/MS) with an API 4000 QTrap mass spectrometer. The scheduled SRM mode demonstrates better results in all fields: more data points per peak, better reproducibility (coefficients of variation (CVs) <5%) and higher signal-to-noise ratio (S/N), even when the number of SRM transitions is doubled. The use of scheduled SRM mode instead of the classical one gives an enhancement of the limits of quantification by a factor two or even higher (up to six), depending on the analyte transitions.

Evaluation of two liquid chromatography/tandem mass spectrometry platforms for quantification of monensin in animal feed and milk

Monensin is an anticoccidial drug that has been used as an additive in medicated feed. The United States Food and Drug Administration (USFDA) has included monensin in the national surveillance schemes for residues in foodstuff. In this study, two simple, selective and rapid methods were developed to determine monensin content in animal feed and milk. The methods enabled the detection of monensin residues as low as 1 ppb. Moreover, the two methods were used as models to compare two common liquid chromatography/tandem mass spectrometry (LC/MS/MS) platforms; an LC linear ion trap (LC/LIT) and an LC triple quadrupole (LC/QqQ). The two instrument platforms were evaluated for their matrix effect dependence, precision and accuracy. The LC/QqQ presented a lower limit of detection and limit of quantitation (LOD and LOQ) and showed less matrix dependence as compared to the LC/LIT. The LC/QqQ instrument also demonstrated a better intermediate precision. For example, the intermediate precision standard deviation calculated for 27 analyses across three days was 4% and 11% for LC/QqQ and LC/LIT, respectively. Overall, the LC/QqQ represents a better choice for analysis of monensin with respect to LOD, LOQ, matrix interference and precision.

Quantification, confirmation and screening capability of UHPLC coupled to triple quadrupole and hybrid quadrupole time-of-flight mass spectrometry in pesticide residue analysis

The potential of three mass spectrometry (MS) analyzers (triple quadrupole, QqQ; time of flight, TOF; and quadrupole time of flight, QTOF) has been investigated and compared for quantification, confirmation and screening purposes in pesticide residue analysis of fruit and vegetable samples. For this purpose, analytical methodology for multiresidue determination of 11 pesticides, taken as a model, has been developed and validated in nine food matrices for the three mass analyzers coupled to ultra high pressure liquid chromatography. In all cases, limits of quantification around 0.01 mg/kg were reached, fulfilling the most restrictive case of baby-food analysis. Regarding absolute sensitivity, the lower limits of detection were obtained, as expected, for QqQ (100 fg), whereas slightly higher limits (300 fg) were obtained for both TOF and QTOF. Confirmative capacity of each analyzer was studied for each analyte based on the identification points (IPs) criterion, useful for a comprehensive comparison. QTOF mass analyzer showed the highest confirmatory capacity, although QqQ normally led to sufficient number of IPs, even at lower concentration levels. The potential of TOF MS was also investigated for screening purposes. To this aim, around 50 commercial fruits and vegetables samples were analyzed, searching for more than 400 pesticides. TOF MS proved to be an attractive analytical tool for rapid detection and reliable identification of a large number of pesticides thanks to the full spectrum acquisition at accurate mass with satisfactory sensitivity. This process is readily boosted when combined with specialized software packages, together with theoretical exact mass databases. Several pesticides (e.g. carbendazim in citrus and indoxacarb in grape) were detected in the samples. Further unequivocal confirmation of the identity was performed using reference standards and/or QTOF MS/MS experiments.

Methods for determining pesticides and polychlorinated biphenyls in food samples--problems and challenges

Determination of residual amounts of pesticides and polychlorinated biphenyls (PCBs) in food samples requires the use of specific techniques regarding sample preparation as well as instrumental analysis which should be characterized by a very low detection limit. A problem associated with the use of pesticides and PCBs is the need for controlling their residues in the environment, particularly in food, as these chemicals show a propensity to accumulate. The analysis of food samples for the presence of pesticides and PCBs brings on many difficulties because of the specificity of sample preparation consisting of multistep purification procedures of samples that contain trace amounts of an analyte. Concentration determinations of pollutants that easily dissolve in complex matrices, particularly in the presence of a large apportionment of interfering substances, pose a big challenge. Therefore, the basic step in food analysis for the presence of pesticides and PCBs is sample preparation which mainly consists of analyte enrichment and the removal of interfering substances. But all steps of the analytical procedure that include sample collection and preparation, extraction of analytes from matrix, extract purification, and final determination, are very significant; their precision and correct application have a decisive effect on the final result.

Pulsed Nano-Electrospray Ionization: Characterization of Temporal Response and Implementation with a Flared Inlet Capillary

The temporal response of pulsed nano-electrospray ionization mass spectrometry (nano-ESI-MS) was studied and its influence on ion formation and detection was characterized. Rise and decay times for the mass resolved ion current were determined to be 20 ± 3 msec and 61 ± 5 msec, respectively, which led to a maximum pulse rate of 12 Hz. Pulsed nano-ESI operation was demonstrated from a multi-sprayer source controlled by a high voltage pulsing circuit constructed in-house. The desired source mode of operation (e.g. pulsing or continuous) can be realized solely by controlling the voltage applied to each sprayer.

Ion trap lC-MS/MS as a valid multi-method to determine trichothecenes and zearalenone in the food industry

In recent years the European Scientific Committee on Food has frequently expressed its opinion on Fusarium toxins, setting limits, regulations and guidelines in order to reduce their levels in raw materials and food commodities. Trichothecenes are known as DNA and mitochondrial metabolism inhibitors, representing the largest group (over 170 compounds) of Fusarium mycotoxins. Zearalenone (ZEA) is also produced by Fusarium species. It is found almost entirely in grains and has a mainly oestrogenic effect. Wheat-based products (such as bread and pasta) are the predominant source of deoxynivalenol (DON) and nivalenol (NIV) intake, while the highest amounts of T-2 and HT-2 toxins were observed mainly in oat-based products. Therefore, food companies are progressively being forced to set up analytical methods in their laboratories for determining these kinds of toxins in an accurate, sensitive and rapid way. Following this issue, we set up a liquid chromatography-electrospray ionisation tandem mass spectrometry (LC-ESI-IonTrap-MS/MS) method for the simultaneous determination of several types of A and B trichothecenes, together with ZEA, minimising the matrix effect by using specific fragmentation parameters in positive or negative ion modes and dedicated internal standards: quantification of trichothecenes was done with isotope substituted (13C15)-deoxynivalenol, while quantification of ZEA was performed by the contemporaneous use of Zearalanone (ZAN). Sample extraction was performed with acetonitrile/water mixtures, MycoSep® columns were used for fast and effective clean-up procedure and detection was carried out in the multiple reaction monitoring (MRM) mode. Spiking blank cereal samples, the method was validated in terms of detection limits (reaching µg/ kg levels), linearity, recovery, precision (RSD<5%) and accuracy. Method performances were finally tested on oat and durum wheat samples. In conclusion, ion trap instruments can currently provide high-throughput LC/MSn mycotoxin analysis where sensitivity, reliability and productivity coexist in an interesting and good compromise for food industry applications.

Analysis of native amino acids by liquid chromatography/electrospray ionization mass spectrometry: comparative study between two sources and interfaces

The analytical performances of two triple-quadrupole instruments, which differ in their atmospheric-pressure sources, were evaluated for native amino acid analysis. The Applied Biosystems/Sciex API 300 instrument was equipped with a turboIon Spray source and a curtain gas interface while the Waters/Micromass Quattro Ultima instrument was characterized by its Z-spray source. Liquid chromatography/mass spectrometry analysis of native amino acids requires volatile ion-pairing mobile phase additives (mainly perfluorinated carboxylic acids). The effects of the structure and concentration of the ion-pairing reagents as well as the organic modifier percentage on the electrospray response of amino acids were studied in detail. The most favourable chromatographic conditions depend strongly on the mass spectrometer used. Several instrumental parameters were also studied, including spray voltage, transmission lens voltages, temperature of desolvation and auxiliary gas flow rates. The results show substantial qualitative differences depending on the instrument geometry. The quantitative performances of the two triple-quadrupole mass spectrometers were evaluated in terms of limits of detection and quantification. The effects of the matrix on the analyte ionization were also examined, and the long-term stability of the electrospray performance was studied over 12 h using a mobile phase containing the perfluorinated ion-pairing reagents. The study provides information on the robustness of the MS instrument and its detection sensitivity towards native amino acid analysis. It appears that each instrument has its good and bad points since one provides higher sensitivity while another is more robust.

Capabilities of different liquid chromatography tandem mass spectrometry systems in determining pesticide residues in food

Three different liquid chromatography-mass spectrometry (LC-MS) instruments equipped with triple quadrupole (QqQ), quadrupole ion trap (QIT) and quadrupole-time-of-flight (QqTOF), suitable to carry out tandem mass spectrometry, were examined to determine pesticide residues in food. Twelve pesticides (acrinathrin, bupirimate, buprofezin, cyproconazole, lambda-cyhalothrin, fluvalinate, hexaflumuron, kresoxim-methyl, propanil, pyrifenox, pyriproxyfen and tebufenpyrad) and six matrices (oranges, strawberries, cherries, peaches, apricots and pears) were taken as model. The comparison was focused on two aspects: the quantitative, covering sensitivity, precision and accuracy as well as the qualitative, checking the possibility to identify any metabolite present in the samples, which were not targeted in the methods. The extraction was carried out using pressurized liquid extraction (PLE) with ethyl acetate and acid alumina. Recoveries were over 70 % for all the analytes. Repeatabilities were better for the QqQ (5-12%) than for QIT (6-15%) and for QqTOF (14-19%). QqQ offered a linear dynamic range of at least three orders of magnitude, whereas those of QIT and QqTOF were two and one orders of magnitude, respectively. QqQ reached at least 20-fold higher sensitivity than QIT and QqTOF. However, the QqQ failed to identify non-target compounds. QIT and QqTOF were able to successfully identify the metabolite of bupirimate, ethirimol. Application to monitor the content in fruits, taken from agricultural cooperatives, and to calculate the estimated daily intake (EDI) to establish if there is any difference of toxicological interest is also reported.

Methods of sample preparation for determination of pesticide residues in food matrices by chromatography-mass spectrometry-based techniques: a review

Much progress has been made in pesticide analysis over the past decade, during which time hyphenated techniques involving highly efficient separation and sensitive detection have become the techniques of choice. Among these, methods based on chromatographic separation with mass spectrometric detection have resulted in greater likelihood of identification and are acknowledged to be extremely useful and authoritative methods for determination of pesticide residues. Even with such powerful instrumental techniques, however, the risk of interference increases with the complexity of the matrix studied, so sample preparation before instrumental analysis is still mandatory in many applications, for example food analysis. This article summarizes the analytical characteristics of the different methods of sample-preparation for determination of pesticide residues in a variety of food matrices, and surveys their recent applications in combination with chromatographic mass spectrometric analysis. We discuss the advantages and the disadvantages of the different methods, address instrumental aspects, and summarize conclusions and perspectives for the future.

Identification and quantitation of pyrethroid pesticide residues in vegetables by solid-phase extraction and liquid chromatography/electrospray ionization ion trap mass spectrometry

A quantitative method consisting of solid-phase extraction (SPE) followed by liquid chromatography/electrospray ionization ion trap mass spectrometry (LC/ESI-ITMS) analysis was developed for the identification and quantitation of ten pyrethroid pesticides commonly used in vegetables. The best HPLC separation was achieved using a gradient program of methanol/water mixture. For the vegetable samples, an SPE procedure to clean up the matrices was carried out prior to LC/MS analysis. Under the optimum conditions, the limits of quantification of the pyrethroid pesticides (tetramethrin, allethrin, fenpropathrin, lambda-cyhalothrin, cypermethrin, deltamethrin, fenvalerate, bioresmethrin, permethrin and bifenthrin) ranged from 0.03 to 0.1 mg kg-1 with relative standard deviations<20%, and the mean recoveries ranged from 69.5 to 102.5%. The proposed method has been successfully applied to the determination of pyrethroids in six vegetables with satisfactory results.

Control of pesticide residues by liquid chromatography-mass spectrometry to ensure food safety

Liquid chromatography-mass spectrometry (LC-MS) has become an invaluable technique for the control of pesticide residues to ensure food safety. After an introduction about the regulations that highlights its importance to meet the official requirements on analytical performance, the different mass spectrometers used in this field of research, as well as the LC-MS interfaces and the difficulties associated with quantitative LC-MS determination, are discussed. The ability to use practical data for quantifying pesticides together with the option of obtaining structural information to identify target and non-target parent compounds and metabolites are discussed. Special attention is paid to the impact of sample preparation and chromatography on the ionization efficiency of pesticides from food. The last section is devoted to applications from a food safety point of view. (c) 2006 Wiley Periodicals, Inc.

Residue analysis of 500 high priority pesticides: better by GC-MS or LC-MS/MS?

This overview evaluates the capabilities of mass spectrometry (MS) in combination with gas chromatography (GC) and liquid chromatography (LC) for the determination of a multitude of pesticides. The selection of pesticides for this assessment is based on the status of production, the existence of regulations on maximum residue levels in food, and the frequency of residue detection. GC-MS with electron impact (EI) ionization and the combination of LC with tandem mass spectrometers (LC-MS/MS) using electrospray ionization (ESI) are identified as techniques most often applied in multi-residue methods for pesticides at present. Therefore, applicability and sensitivity obtained with GC-EI-MS and LC-ESI-MS/MS is individually compared for each of the selected pesticides. Only for one substance class only, the organochlorine pesticides, GC-MS achieves better performance. For all other classes of pesticides, the assessment shows a wider scope and better sensitivity if detection is based on LC-MS.

Time of flight mass spectrometry applied to the liquid chromatographic analysis of pesticides in water and food

Liquid chromatography coupled to mass spectrometry (LC-MS) is an excellent technique to determine trace levels of polar and thermolabile pesticides and their degradation products in complex matrices. LC-MS can be equipped with several mass analyzers, each of which provides unique features capable to identify, quantify, and resolve ambiguities by selecting appropriate ionization and acquisition parameters. We discuss in this review the use of LC coupled to (quadrupole) time-of-flight mass spectrometry (LC-(Q)ToF-MS) to determine the presence of target and non-target pesticides in water and food. This technique is characterized by operating at a resolving power of 10,000 or more. Therefore, it gives accurate masses for both parent and fragment ions and enables the measurement of the elemental formula of a compound achieving compound identification. In addition, the combination of quadrupole-ToF permits tandem mass spectrometry, provides more structural information, and enhances selectivity. The purpose of this article is to provide an overview on the state of art and applicability of liquid chromatography time-of-flight mass spectrometry (LC-ToF-MS), and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) for the analysis of pesticides in environmental matrices and food. The performance of such techniques is depicted in terms of accurate mass measurement, fragmentation, and selectivity. The final section is devoted to describing the applicability of LC-(Q)ToF-MS to routine analysis of pesticides in food matrices, indicating those operational conditions and criteria used to screen, quantify, and identify target and "suspected" pesticides and their degradation products in water, fruits, and vegetables. The potential and future trends as well as limitations of LC-(Q)ToF-MS for pesticide monitoring are highlighted.

Analysis of amitrole by normal-phase liquid chromatography and tandem mass spectrometry using a sheath liquid electrospray interface

The coupling of normal-phase liquid chromatography to tandem mass spectrometry, previously developed in our laboratory, has been applied to the analysis of amitrole. This coupling utilizes an electrospray interface modified to accommodate the introduction of a make-up solution at the tip of the electrospray probe. A methanolic solution containing 3 mM ammonium acetate delivered at a flow rate of 10 microL . min(-1) was found to be the optimal sheath liquid to promote successful ionization of the amitrole. Protonated molecules, arising from in-source dissociation of ammonium adducts, were subjected to tandem mass spectrometric experiments in a triple-quadrupole instrument. The main fragmentation reactions were characterized and selected to acquire chromatographic data in the multiple reaction monitoring mode. The limit of detection for amitrole was in the ppm range without any preconcentration step. Enhanced efficiency of ion transmission achievable nowadays in mass spectrometers (this analytical configuration was developed with a 15-year-old instrument) is reasonably expected to further improve this detection level.

Comparison of four mass analyzers for determining carbosulfan and its metabolites in citrus by liquid chromatography/mass spectrometry

Four liquid chromatography/mass spectrometry (LC/MS) systems, equipped with single quadrupole, triple quadrupole (QqQ), quadrupole ion trap (QIT) and quadrupole time-of-flight (QqTOF) mass analyzers, were evaluated for the analysis of carbosulfan and its main transformation products. The comparison of quantitative aspects (sensitivity, precision and accuracy) was emphasized. Results showed that the triple quadrupole instrument reaches at least 20-fold higher sensitivity (LOD from 0.04 to 0.4 microg kg(-1)) compared to the single quadrupole (4-70 microg kg(-1)), the QIT (4-25 microg kg(-1)) and the QqTOF (4-23 microg kg(-1)) instruments. Recoveries were over 70% for all the analytes, except dibutylamine and 7-phenolcarbofuran. Repeatabilities (within-day) were slightly better by the single quadrupole (5-10%) and the QqQ (5-9%) than by the QIT (12-16%) and the QqTOF (9-16%). Both the QqTOF and QIT offer a linear dynamic range of two orders of magnitude whereas the single quadrupole and QqQ of, at least, three orders of magnitude. The method was applied to analyze carbosulfan field-treated orange samples, in which carbosulfan, carbofuran, 3-hydroxycarbofuran, and dibutylamine were found. As an example, the mean carbosulfan concentration was 20 +/- 0.6 microg kg(-1) measured by the QqQ, 22 +/- 1.2 microg kg(-1) by the single quadrupole, 25 +/- 2.8 microg kg(-1) by the QIT, and 20 +/- 1.8 microg kg(-1) by the QqTOF. Although the QqQ is more sensitive and precise, the mean values obtained by the four instruments are acceptable and comparable. The potential of each technique for the verification of the identity of residues detected in oranges is discussed using the concept of identification points.

Analysis of pesticides in fruits by pressurized liquid extraction and liquid chromatography–ion trap–triple stage mass spectrometry

A multi-residue method using pressurized liquid extraction (PLE) and liquid chromatography-quadrupole ion trap-triple stage mass spectrometry (LC-IT-MS(3)) has been developed for determining trace levels of pesticides in fruits. The selected pesticides can be distinguished in: benzimidazoles and azoles, organophosphorus, carbamates, neonicotinoids, and acaricides. PLE has been optimized to extract these pesticide residues from oranges and peaches by studying the effect of experimental variables on PLE efficiency. Samples were extracted at high temperature and pressure (75 degrees C and 1500psi) using ethyl acetate as extraction solvent and acidic alumina as drying agent. The recoveries obtained by PLE ranged from 58% to 97% and the relative standard deviation (RSDs) from 5% to 19%. The limits of quantification (LOQs) of the compounds were from 0.025 to 0.25mgkg(-1), which are well-below the maximum residue limits (MRLs) established by the European Union (EU) and the Spanish legislations.

Routine application using single quadrupole liquid chromatography–mass spectrometry to pesticides analysis in citrus fruits

A rapid and sensitive liquid chromatography-electrospray ionization-mass spectrometry method has been developed for the routine analysis of buprofezin, bupirimate, hexaflumuron, tebufenpyrad, fluvalinate and pyriproxyfen in citrus fruits. Extracts were obtained by matrix solid-phase dispersion (MSPD) using C18 as dispersant and dichloromethane-methanol (80:20, v/v) as eluent. Matrix effects were tested for all matrices by addition of standard to sample blank extracts (samples containing no detectable residues). Mean recoveries obtained at fortification levels between 0.01 and 5 mg kg(-1) were 57-97% with relative standard deviations (RSDs) from 5 to 19%. The limits of quantification (LOQ) were in the range of 0.01-0.2 mg kg(-1) and lower than maximum residue limits (MRLs) established by the Spanish legislation. The MSPD was compared with conventional ethyl acetate extraction, showing equivalent recoveries and precision. Although the sample is more concentrated (5-fold) by solid-liquid extraction (SLE) with ethyl acetate than by MSPD, LOQs obtained by both techniques, were almost equal, because MSPD reduces matrix effects, baseline noise, and interfering peaks from the matrix. The proposed method has been applied to the determination of selected pesticides in real samples. Liquid chromatography-tandem mass spectrometry (LC-MS-MS) with quadrupole ion trap (QIT) and triple quadrupole (TQ) have been used as confirmatory tool for positive samples according to a recent No. SANCO/10476/2003 European Union Guideline.