Negative chemical ionization gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry and automated accurate mass data processing for determination of pesticides in fruit and vegetables.

Gas chromatography coupled to high resolution hybrid quadrupole time-of-flight mass spectrometry (GC-QTOF MS), operating in negative chemical ionization (NCI) mode and combining full scan with MSMS experiments using accurate mass analysis, has been explored for the automated determination of pesticide residues in fruit and vegetables. Seventy compounds were included in this approach where 50 % of them are not approved by the EU legislation. A global 76 % of the analytes could be identified at 1 µg kg(-1). Recovery studies were developed at three concentration levels (1, 5, and 10 µg kg(-1)). Seventy-seven percent of the detected pesticides at the lowest level yielded recoveries within the 70 %-120 % range, whereas 94 % could be quantified at 5 µg kg(-1), and the 100 % were determined at 10 µg kg(-1). Good repeatability, expressed as relative standard deviation (RSD <20 %), was obtained for all compounds. The main drawback of the method was the limited dynamic range that was observed for some analytes that can be overcome either diluting the sample or lowering the injection volume. A home-made database was developed and applied to an automatic accurate mass data processing. Measured mass accuracies of the generated ions were mainly less than 5 ppm for at least one diagnostic ion. When only one ion was obtained in the single-stage NCI-MS, a representative product ion from MSMS experiments was used as identification criterion. A total of 30 real samples were analyzed and 67 % of the samples were positive for 12 different pesticides in the range 1.0-1321.3 µg kg(-1).

Validation of a multiclass multiresidue method and monitoring results for 210 pesticides in fruits and vegetables by gas chromatography-triple quadrupole mass spectrometry.

A rapid, sensitive, accurate and reliable multiresidue method for the identification and quantification of 210 relevant pesticides in four representative fruit and vegetable commodities (tomato, potato, spring onion and orange) has been developed and validated by gas chromatography in tandem with triple quadrupole mass spectrometry. The method has been fully validated and applied to 292 samples from different countries. Prior to instrumental analysis, an extraction procedure based on a sample extraction of multiclass analytes, using the ethyl acetate method was employed. Mass spectrometric conditions were individually optimized for each compound in the selected reaction monitoring (SRM) mode to achieve maximum sensitivity. The pesticides were separated in less than 25 min. This was followed by an exhaustive control of the retention times. The Retention Time Locking Method was applied, working at a constant pressure throughout the analysis. System maintenance was reduced by using a purged capillary flow device that provided backflush capabilities by reversing column flow immediately after elution of the last compound of interest. Istotopically labelled internal standards were employed to improve the quality of the analytical results.

Evaluation of zirconium dioxide-based sorbents to decrease the matrix effect in avocado and almond multiresidue pesticide analysis followed by gas chromatography tandem mass spectrometry.

Two sorbents containing ZrO2 (Z-Sep and Z-Sep+) were tested as a d-SPE clean-up in combination with the QuEChERS and ethyl acetate multiresidue method in the pesticide residues extraction in avocado. All extracts were analysed using gas chromatography coupled with a triple quadrupole mass spectrometer working in multi-reaction monitoring mode. GC QToF was used to compare the amount of matrix compounds present in the final extracts, prepared according to different protocols. The highest number of pesticides with acceptable recoveries and the lowest amount of coextracted matrix compounds were provided by QuEChERS with Z-Sep. Subsequently, this method was fully validated in avocado and almonds. Validation studies were carried out according to DG Sanco guidelines including: the evaluation of recoveries at two levels (10 and 50 µg/kg), limit of quantitation, linearity, matrix effects, as well as interday and intraday precision. In avocado, 166 pesticides were fully validated compared to 119 in almonds. The method was operated satisfactorily in routine analysis and was applied to real samples.

Comparison of three multiresidue methods to analyse pesticides in green tea with liquid and gas chromatography/tandem mass spectrometry.

The aim of the present work was to compare and choose the best method to extract pesticide residues from green tea. Three different multiresidue methods were tested on blank green tea samples fortified with 86 pesticides (insecticides, fungicides and herbicides) at the 100 µg kg(-1) level - modified QuEChERS (in order to limit the amount of coextractives, MgSO(4) was replaced with calcium chloride in the clean-up step); ethyl acetate extraction (not SweEt) and miniLuke. Due to matrix complexity, samples were diluted five times. The extracts were analysed by GC-MS/MS and LC-MS/MS. During the experiment recoveries, the precision and influence of coextracted compounds were compared. The study carried out on the three methods showed that the best results were achieved using QuEChERS. In terms of recoveries, QuEChERS showed the highest performance - successfully analysing 75 compounds (87% of the total number) with recoveries from 70 to 120% - whereas the miniLuke and ethyl acetate methods had 54 (63% of the total number) and 31 (36% of the total number), respectively. In addition, QuEChERS extracts contained the least amount of co-extracted matrix components. All three methods provided very good precision.

Pesticide analysis in teas and chamomile by liquid chromatography and gas chromatography tandem mass spectrometry using a modified QuEChERS method: validation and pilot survey in real samples.

This paper presents the validation of a modified QuEChERS method in four matrices - green tea, red tea, black tea and chamomile. The experiments were carried out using blank samples spiked with a solution of 86 pesticides (insecticides, fungicides and herbicides) at four levels - 10, 25, 50 and 100 µg/kg. The samples were extracted according to the citrate QuEChERS protocol; however, to reduce the amount of coextracted matrix compounds, calcium chloride was employed instead of magnesium sulphate in the clean-up step. The samples were analysed by LC-MS/MS and GC-MS/MS. Included in the scope of validation were: recovery, linearity, matrix effects, limits of detection and quantitation as well as intra-day and inter-day precision. The validated method was used in a real sample survey carried out on 75 samples purchased in ten different countries. In all matrices, recoveries of the majority of compounds were in the 70-120% range and were characterised by precision lower than 20%. In 85% of pesticide/matrix combinations the analytes can be detected quantitatively by the proposed method at the European Union Maximum Residue Level. The analysis of the real samples revealed that large number of teas and chamomiles sold in the European Union contain pesticides whose usage is not approved and also pesticides in concentrations above the EU MRLs.

Benefits and pitfalls of the application of screening methods for the analysis of pesticide residues in fruits and vegetables.

The goal of this study was to expand knowledge on the performance of screening methods based on accurate mass measurements using a liquid chromatography electrospray quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS) system operating in full scan mode and with automatic identification based on the use accurate-mass databases. The study involved the analysis of 97 pesticides, in five matrices (tomato, pepper, zucchini, orange and leek) and at three concentration levels (20, 50 and 100 µg kg(-1)). Aspects concerning optimization of the search parameters, sensitivity, matrix effects, efficiency of the algorithm search, usefulness of fragment ions, etc., are evaluated in deep. Sensitivity requirements have been identified as the main obstacle affecting the automatic identification of pesticides, especially in complex matrices, where the ionization suppression reduces the detectability of analytes. In addition, we have detected some failures in the software used for automatic data processing in terms of analysis of isobaric compounds, use of isotopic clusters, spectral deconvolution and data processing speed that hamper the correct identification in some pesticide/matrix combinations. These drawbacks should be improved in the future for its effective implementation in routine residue analysis.

Chemical and toxicological evolution of the antibiotic sulfamethoxazole under ozone treatment in water solution.

This work studied the elimination paths of the sulfonamide antibiotic sulfamethoxazole by ozonation in fast kinetic regime. The ozonation runs were performed in conditions favouring either the direct attack of the ozone molecule or the indirect attack by ozone-generated radical species with initial concentration of 0.150 mM. When doses of ozone were transferred to the liquid phase 0.2mM, in no case did sulfamethoxazole remain in solution. Two main transformation pathways were found involving the preferential attack of molecular ozone or radical pathway and leading to the formation of six intermediates, which were identified by LC-ESI-QTOF-MS. Both routes took place simultaneously in the different conditions tested, leading to a hydroxylation reaction of the benzene ring, oxidation of the amino group on the benzene ring, oxidation of the methyl group and the double bond in the isoxazole ring and S-N bond cleavage. The most abundant reaction intermediate was that resulting from S-N bond cleavage. The toxicity of partially ozonated samples for Daphnia magna and Pseudokirchneriella subcapitata revealed the formation of toxic by-products during the early stages of reaction and the persistence of considerable toxicity after the total depletion of sulfamethoxazole.

Evaluation of relevant time-of-flight-MS parameters used in HPLC/MS full-scan screening methods for pesticide residues.

An automatic screening method based on HPLC/time-of-flight (TOF)-MS (full scan) was used for the analysis of 103 non-European fruit and vegetable samples after extraction by the quick, easy, cheap, effective, rugged, and safe method. The screening method uses a database that includes 300 pesticides, their fragments, and isotopical signals (910 ions) that identified 210 pesticides in 78 positive samples, with the highest number of detection being nine pesticides/sample. The concentrations of 97 pesticides were <10 microg/kg, 53 were between 10 and 100 microg/kg, and 60 were at a concentration of >100 microg/kg. Several parameters of the automatic screening method were carefully studied to avoid false positives and negatives in the studied samples; these included peak filter (number of chromatographic peak counts) and search criteria (retention time and error window). These parameters were affected by differences in mass accuracy and sensitivity of the two HPLC/TOF-MS systems used with different resolution powers (15 000 and 7500), the capabilities of which for resolving the ions included in the database from the matrix ions were studied in four matrixes, viz., pepper, rice, garlic, and cauliflower. Both of these mass resolutions were found to be satisfactory to resolve interferences from the signals of interest in the studied matrixes.

Comparative study of the main top-down approaches for the estimation of measurement uncertainty in multiresidue analysis of pesticides in fruits and vegetables.

Practical "top-down" approaches appear to be the most suitable for the evaluation of measurement uncertainty in pesticide residue testing laboratories, where analytical procedures are routinely applied to a large number of pesticide/food combinations. The opposite approach, "bottom-up" evaluation of measurement uncertainty, leads to great difficulties in evaluating all of the pesticides in a consistent way. Among the top-down approaches, there are two main ways in which measurement uncertainty can be estimated: One is based on default values, which are based on previous extensive interlaboratory experience and the proven accuracy of the laboratory; these include the Horwitz equation or the fit-for-purpose relative standard deviation (FFP-RSD). The other is based on experimental data from the quality control work of the laboratory: within-laboratory reproducibility, interlaboratory validation, or a combination of results obtained in proficiency tests. The principal existing guidelines from various bodies (Eurachem, Nordtest, and Eurolab) all propose different approaches for calculating measurement uncertainty. In this paper, the main top-down approaches are evaluated and compared using the data from the European Proficiency Test Database for Fruits and Vegetables and the Multiresidue Method validation databases obtained from the National Reference and Official Laboratories in Europe. The main conclusion of the comparative study is that a default expanded measurement uncertainty value of 50% could satisfy all of the requirements for facilitating and harmonizing, worldwide, the intercomparability of the pesticide residue confidence results between laboratories.

Efficiency evaluation of the main multiresidue methods used in Europe for the analysis of amitraz and its major metabolites.

This paper compares the performance of the three most widely employed multiresidue methods [quick, easy, cheap, effective, rugged, and safe (QuEChERS), mini-Luke, and ethyl acetate] currently used for the determination of amitraz residues in fruits. A fast and differentiated analysis of amitraz and its two main metabolites, N-2,4-dimethylphenyl-N-methylformamidine and 2,4-dimethylformanilide, was performed by HPLC-electrospray ionization-MS/MS using a triple quadrupole mass spectrometer in the positive mode. A test of the stability of the standard solutions showed a rapid hydrolysis of amitraz to the amide and amidine derivatives in solutions containing water, including QuEChERS extracts of crops that were previously acidified. Two useful mass transitions were used to confirm the presence of each analyte in the sample extracts. LOD values ranging from 0.4 to 2.0 microglkg were obtained. Linearity of response over 2 orders of magnitude was demonstrated (r2 > 0.999) in solvent and pear extract. The recovery studies were performed on pear blanks spiked at two concentration levels, 50 and 500 microg/kg (n = 5). Best recoveries, ranging from 75 to 103%, were obtained by the application of the QuEChERS method with CV < 8% in all cases. The QuEChERS method was applied to a monitoring study carried out by the Chemical and Veterinary Investigation Office Stuttgart laboratory. From the 63 pear samples analyzed, 21 contained amitraz residues (expressed as sum) ranging from 0.02 to 2.9 mg/kg. Amitraz parent was detected only in a few cases at very low concentration levels, with N-2,4-dimethylphenyl-N-methylformamidine being the metabolite almost entirely representing the total residue. These results emphasize that the residue situation is clearly underestimated if only the parent compound is targeted, and they reinforce how important it is to include amitraz in the target scope of pesticide residue laboratories, especially since the concentrations detected exceeded the Acute Reference Dose in the majority of cases and pose a health risk to the consumer.

Multi-residue determination of pesticides in fruit-based soft drinks by fast liquid chromatography time-of-flight mass spectrometry.

This work reports a rapid and reliable method for the determination of 33 multi-class pesticides in fruit-based soft drinks. The proposed method consists of a sample treatment step based on solid-phase extraction using hydrophilic-lipophilic balanced polymer-based reverse-phase SPE cartridges, followed by identification and quantitation of the target pesticides by rapid resolution liquid chromatography using a short C(18) column (4.6mm x 50mm) with 1.8microm particle size and mass spectrometric detection using electrospray time-of-flight mass spectrometry (LC-TOFMS). The identification and confirmation of the compounds were based on retention time matching along with the accurate mass measurements of the protonated molecules ([M+H](+)) and their main fragment ions. Fruit-based soft drinks spiked at different fortification levels (10 and 50microgL(-1)) yielded average recoveries in the range 66-124% with RSD (%) below 14% (n=6). The obtained limits of quantitation varied in the range 0.02-2microgL(-1). The proposed method was successfully applied to the analysis of 14 market-purchased fruit-based soft drinks samples collected in some European countries, showing its potential applicability and revealing the presence of some of the target species in the microgL(-1) range.

Accurate-mass databases for comprehensive screening of pesticide residues in food by fast liquid chromatography time-of-flight mass spectrometry.

Because of the international trade of fruits and vegetables and the lack of harmonized regulations on the use of pesticides worldwide, the development of comprehensive screening methods for analyzing hundreds of pesticides and other banned chemicals is very convenient. This work reports the development and evaluation of a rapid automated screening method for determining pesticide residues in food using liquid chromatography electrospray time-of-flight mass spectrometry (LC-TOFMS) based on the use of an accurate-mass database. The database created includes data not only on the accurate masses of the target ions but also the characteristic in-source fragment ions (over 400 fragments included) and retention time data. This customized database was associated to commercially available software which extracted all the potential compounds of interest from the LC-TOFMS raw data of each sample and matched them against the database to search for targeted compounds in the sample. This automatic screening method requires a careful optimization of the accurate-mass window and retention time tolerances, which play a determinant role on the selectivity, accuracy, and throughput of the whole procedure. Values of 10 mDa for preliminary screening and 1 mDa/5 ppm for confirmation along with a +/-0.15 min retention time window were found to be optimum for the compounds and samples tested. The optimized methods enable the automated screening of ca. 300 compounds in less than 20 min including the LC-MS run and data processing. The proposed method was applied to 60 real samples, and the results of the positive findings compared well with those obtained using a liquid chromatography tandem mass spectrometry (LC-MS/MS) method (triple quadrupole). The rates obtained on the identification of compounds in spiked and real samples in an automated fashion at different concentration levels were over 95% of the compounds, thus revealing as a convenient tool for the large-scale screening of pesticides in foodstuffs.

Simultaneous screening and target analytical approach by gas chromatography-quadrupole-mass spectrometry for pesticide residues in fruits and vegetables.

A full-scan GC/quadrupole/MS method has been developed to perform large-scale screenings of pesticides and simultaneous quantification of 95 target compounds in a single run of 21 min. The screening method was performed by using a deconvolution of the spectrum of the full-scan data files acquired under a retention time locked method. The identification performance of the screening method was evaluated in eight different food matrixes at three different concentrations. The system was equipped with a programmable temperature vaporizing inlet, allowing 10 microL injections. The LOQ in the full-scan mode and linearity were studied for four different matrixes. Correlation coefficients > 0.99 were achieved in all cases, and the LOD was < 20 microg/kg for 80% of the studied pesticides. Maintenance of the system was reduced by the use of a QuickSwap device that provided backflush capabilities by reversing column flow immediately after elution of the last compound of interest. The combined screening and target method was used in the analysis of more than 100 food samples, including a carrot sample from the European Proficiency Test FV 10, with good results.

Determination of PASHs by various analytical techniques based on gas chromatography-mass spectrometry: application to a biodesulfurization process.

Polycyclic aromatic sulphur heterocyclic (PASH) compounds, such as dibenzothiophene (DBT) and alkylated derivatives are used as model compounds in biodesulfurization processes. The development of these processes is focused on the reduction of the concentration of sulphur in gasoline and gas-oil [D.J. Monticello, Curr. Opin. Biotechnol. 11 (2000) 540], in order to meet European Union and United States directives. The evaluation of biodesulfurization processes requires the development of adequate analytical techniques, allowing the identification of any transformation products generated. The identification of intermediates and final products permits the evaluation of the degradation process. In this work, seven sulfurated compounds and one non-sulfurated compound have been selected to develop an extraction method and to compare the sensitivity and identification capabilities of three different gas chromatography ionization modes. The selected compounds are: dibenzothiophene (DBT), 4-methyl-dibenzothiophene (4-m-DBT), 4,6-dimethyl-dibenzothiophene (4,6-dm-DBT) and 4,6 diethyl-dibenzothiophene (4,6 de-DBT), all of which can be used as model compounds in biodesulfurization processes; as well as dibenzothiophene sulfoxide (DBTO(2)), dibenzothiophene sulfone (DBTO) and 2-(2-hydroxybiphenyl)-benzenesulfinate (HBPS), which are intermediate products in biodesulfurization processes of DBT [ A. Alcon, V.E. Santos, A.B. Martín, P. Yustos, F. García-Ochoa, Biochem. Eng. J. 26 (2005) 168]. Furthermore, a non-sulfurated compound, 2-hydroxybiphenyl (2-HBP), has also been selected as it is the final product in the biodesulfurization process of DBT [A. Alcon, V.E. Santos, A.B. Martín, P. Yustos, F. García-Ochoa. Biochem. Eng. J. 26 (2005) 168]. Since, typically, biodesulfurization reactions take place in a biphasic medium, two extraction methods have been developed: a liquid-liquid extraction method for the watery phase and a solid phase extraction method for the organic phase. Recoveries of the selected compound in both media were studied. They were in the range of 80-100% for the watery and in the range of 40-60% for the organic phase, respectively. Gas chromatography coupled to mass spectrometry (GC-MS) has been employed for the identification of these selected compounds. Three different ionization modes were applied: conventional electron impact (EI); positive chemical ionization (PCI), using methane as the reagent gas; and a recently developed ionization mode known as hybrid chemical ionization (HCI), using perfluorotri-n-butylamine as the reagent gas. Limits of detection and identification capabilities have been compared between the three analytical techniques. The sensitivity of the three analytical techniques was studied and LOD between 0.05 and 1, between 0.09 and 2 and between 0.001 and 0.043 were achieved for PCI, EI and HCI, respectively. The developed method was applied in samples from a biodesulfurization process. The biodesulfurization reactions were conducted in resting cell operation mode, using Erlenmeyer flasks or an agitated tank bioreactor. The microorganism employed was Pseudomonas putida CECT 5279. The reaction was performed under controlled air flow, stirring and temperature conditions.

Determination of selected non-authorized insecticides in peppers by liquid chromatography time-of-flight mass spectrometry and tandem mass spectrometry.

In this work, two analytical methods based on liquid chromatography coupled to electrospray time-of-flight mass spectrometry (LC/ESI-TOFMS) and tandem mass spectrometry (LC/ESI-MS/MS) are described for the identification, confirmation and quantitation of three insecticides non-authorized in the European Union (nitenpyram, isocarbophos and isofenphos-methyl) but detected in recent monitoring programmes in pepper samples. The proposed methodologies involved a sample extraction procedure using liquid-liquid partition with acetonitrile followed by a cleanup step based on dispersive solid-phase extraction. Recovery studies performed on peppers spiked at different fortification levels (10 and 50 microg kg(-1)) yielded average recoveries in the range 76-100% with relative standard deviation (RSD) (%) values below 10%. Identification, confirmation and quantitation were carried out by LC/TOFMS and LC/MS/MS using a hybrid triple quadrupole linear ion trap (QqLIT) instrument in multiple-reaction monitoring (MRM) mode. The obtained limits of quantitation (LOQs) were in the range 0.1-5 microg kg(-1), depending on each individual technique. Finally, the proposed methods were successfully applied to the analysis of suspected pepper samples.

Photodegradation study of three dipyrone metabolites in various water systems: identification and toxicity of their photodegradation products.

The photochemical behaviour of three relevant metabolites of the analgesic and antipyretic drug dipyrone, 4-methylaminoantipyrine (4-MAA), 4-formylaminoantipyrine (4-FAA) and 4-acetylaminoantipyrine (4-AAA), was evaluated under simulated solar irradiation (Suntest system). For 4-MAA, different aqueous solutions (synthetic seawater, freshwater and Milli-Q water) as well as different operational conditions were compared. According to the experimental results, 4-MAA resulted as being an easily degraded molecule by direct photolysis, with half-life times (t1/2) ranging from 0.12 to 0.58 h, depending on the irradiation conditions. Faster degradation was observed in synthetic waters, suggesting that the photolysis was influenced by the salt composition of the waters. However, no effect on the degradation rate was observed by the presence of natural photosensitizers (dissolved organic matter, nitrate ions). 4-FAA and 4-AAA showed slower photodegradation kinetics, with t1/2 of 24 and 28 h, respectively. A study of photoproduct identification was carried out by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) (ESI positive mode), which allowed us to propose a tentative photodegradation pathway for 4-MAA and the identification of persistent by-products in all the cases. Finally, the application of an acute toxicity test (Daphnia magna) showed an increase in toxicity during the photolytic process, a consequence of the formation of toxic photoproducts.

Determination of postharvest fungicides in fruit juices by solid-phase extraction followed by liquid chromatography electrospray time-of-flight mass spectrometry.

A multiresidue method using liquid chromatography-time-of-flight mass spectrometry (LC-TOFMS) has been developed for the quantitative analysis of five widely used postharvest fungicides (carbendazim, thiabendazole, imazalil, prochloraz, and iprodione) and two of their transformation products (imazalil and prochloraz metabolites) in fruit juices. LC-TOFMS in positive electrospray ionization mode was used to quantify and confirm trace levels of these fungicides in fruit juices. The proposed method consists of a sample treatment step based on solid-phase extraction using hydrophilic-lipophilic-balanced polymer-based reverse-phase SPE cartridges (Oasis HLB) and methanol as an eluting solvent. Fruit-juice extracts spiked at different fortification levels (10 and 20 microg L(-1)) yielded average recoveries in the range of 71-109% with RSD (%) below 15%. Subsequent identification, confirmation, and quantitation were carried out by LC-TOFMS analysis. The confirmation of the target species was based on accurate mass measurements of protonated molecules ([M+H]+) and fragment ions, obtaining routine accuracy errors lower than 2 ppm in most cases. The obtained limits of detection (LODs) of the proposed method were in the range of 0.08-0.45 microg L(-1). Finally, the proposed method was successfully applied to the analysis of 23 fruit juice samples collected from different European countries and the United States, showing the potential applicability of the method in routine analysis. Over 50% of the samples tested contained pesticide residues, but relatively low concentration levels were found.

Chromatographic methods applied in the monitoring of biodesulfurization processes--state of the art.

Analytical methodologies employed in biodesulfurization processes have been reviewed; attention is primarily focused on the use of analytical techniques in the identification of degradation products and on the monitoring of degradation processes in which microbial sulphur-specific transformations take place. This is the first review of analytical techniques applied to biodesulfurization processes. Methodologies based on gas chromatography (GC) are the most frequently employed, in tandem with various detectors, mainly with the mass spectrometry (MS) detector, and the flame ionization detector (FID). High performance liquid chromatography (HPLC) coupled with ultra violet (UV) detection has also been widely employed. Different sulphurated compounds are used as model in biodesulphurization processes, naphtothiophene (NTH), benzothiophene (BTH), alkylated BTH, dibenzothiophene (DBT), alkylated DBT and their transformation products has been reviewed. DBT is the most frequently employed.

Application of ultra performance liquid chromatography-tandem mass spectrometry to the analysis of priority pesticides in groundwater.

Ultra performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UPLC-MS/MS) has been applied for the accurate and rapid analysis of nine trace level priority pesticides in water. The UPLC technology, based on the use of columns packed with 1.7 microm porous particles combined with higher pressures than those conventionally applied in HPLC, enabled to improve in peak resolution, sensitivity and speed of analysis. UPLC chromatograms showed very sharp peaks with less than 2 s wide at the base, except for alachlor. This enhanced efficiency resulted in an increased separation speed of the whole UPLC-MS/MS procedure that required less than 5 min. Limits of detection, determined for 300 ml water samples after SPE preconcentration were in the range between 0.1 and 20 ng/L. The presence of matrix effects or ion suppression was checked by the obtaining of calibration curves in both pure solvent and matrix matched standards. Other performance characteristics of the method, such as linearity and precision were also satisfactory. Finally, the method was successfully applied to the analysis of two water samples from an inter-laboratory exercise.

Multi-residue pesticide analysis in fruits and vegetables by liquid chromatography-time-of-flight mass spectrometry.

In this work, a new multi-residue methodology using liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) for the quantitative (routine) analysis of 15 pesticide residues has been developed. The analytical performance of the method was evaluated for different types of fruit and vegetables: pepper, broccoli, tomato, orange, lemon, apple and melon. The accurate mass measurements were compared in different matrices at significantly different concentration levels (from 0.01 to 0.5 mg/kg) obtaining accuracy errors lower than 2 ppm, which is well within the accepted limits for elemental confirmation. Linearity of response over two orders of magnitude was demonstrated (r > 0.99). Matrix effects resulting in suppression or enhancement of the response were frequently observed, most notably in broccoli and citrus. Instrumental limits of detection (LOD) were between 0.0005 and 0.03 mg/kg depending on the commodity and pesticide studied, all being within European Union regulations for food monitoring program. Finally, the methodology was applied to the analysis of two samples from an inter-laboratory exercise. The high degree of confirmation for target pesticides by accurate mass measurements demonstrated the applicability of the method in routine analysis. This study is a valuable indicator of the potential of LC-TOF-MS for quantitative multi-residue analysis of pesticides in vegetables and fruits.