Łukasz Rajski

Determination of pesticide residues in high oil vegetal commodities by using various multi-residue methods and clean-ups followed by liquid chromatography tandem mass spectrometry.

Several extraction methods were evaluated in terms of recoveries and extraction precision for 113 pesticides in avocado: QuEChERS with various d-SPE clean-ups (Z-Sep, Z-Sep+, PSA+C18 and silica), miniLuke and ethyl acetate. Extracts were analysed using liquid chromatography coupled with triple quadrupole mass spectrometer working in multi-reaction monitoring mode. Z-Sep and Z-Sep+ are new types of material for high lipid matrices - these two sorbents contain ZrO2, which improves fat removal from the extracts. The QuEChERS protocol with Z-Sep provided the highest number of pesticides with recoveries in the 70-120% range along with the lowest amount of coextracted matrix compounds. Subsequently, this method was validated in two matrices - avocado and almonds. In the validation recoveries at two levels - 10 and 50μg/kg - limit of quantitation, linearity, matrix effects, as well as the inter- and intraday precision were studied. In the avocado samples, 107 analytes had LOQs equal to 10μg/kg (signal to noise of quantitative transition was equal 20 or more). In the almond samples, 92 pesticides had LOQs equal to 10μg/kg (S/N≥20) and 2 pesticides at 50μg/kg. The validated method was employed in the analysis of real avocado and almond samples.

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.

Large pesticide multiresidue screening method by liquid chromatography-Orbitrap mass spectrometry in full scan mode applied to fruit and vegetables.

The present work is focused on evaluating the main operational parameters for multiresidue screening of an Orbitrap mass spectrometer for pesticide residue analysis in fruits and vegetables. Operational parameters such as resolution, software for the automatic detection, mass tolerance and retention time extraction window, along with the analytical performance, were evaluated in an updated UHPLC-Orbitrap-mass spectrometer working in full scan mode. The evaluation was performed using QuEChERS extracts of tomato, pepper, orange and green tea. The extracts were spiked with 170 selected pesticides at four concentration levels (10μg/kg, 50μg/kg, 100μg/kg and 500μg/kg). Extracts were diluted 5 fold before injection. Three different resolution settings (17,500, 35,000 and 70,000) were evaluated at various concentration levels. At 10μg/kg, using a resolution of 17,500 and 5ppm of mass tolerance, the detected pesticide rates were from 91% in tomato, to 83% in green tea. These percentages increased at higher resolution values. A resolution of 70,000 was adequate for such analysis even when a small percentage of false detect at low concentration was obtained. The rates of detected compounds increased and were from 98% in tomato to 88% in green tea. Mass tolerance of 5ppm was the most adequate for screening purposes. The observed false negative detects were mainly a consequence of a lack of compound sensitivity exacerbated by ion suppression effects in the experimental conditions applied. With reporting limits of 10μg/kg, reproducibility improved with resolution levels of 35,000 or higher. Linearity was investigated in the 2-100ng/mL (equivalent to 10-500μg/kg in the sample) range. Particularly good automatic screening effectiveness was obtained using the selected settings in the analysis of real samples where no false negatives detects and 5% of false positives detects were obtained.

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.

Liquid chromatography Orbitrap mass spectrometry with simultaneous full scan and tandem MS/MS for highly selective pesticide residue analysis.

This paper describes the application of LC/Q-Orbitrap MS for the analysis of pesticide residues in fruit and vegetable commodities. LC/Q-Orbitrap MS working in full scan simultaneously with a single MS/MS scan was used to analyse 139 pesticide residues in QuEChERS extracts of tomato, pepper, orange and green tea. Full scan data were obtained at a resolution of 70,000 whereas MS/MS data were obtained at a resolution of 17,500. Quantitation and detection was carried out using full scan data while MS/MS data were used only for identification. MS/MS scans did not have a negative influence on quantitation under the applied conditions. Some peak area reproducibility problems were the consequence of the low sensitivity for some compounds (aldicarb, chlorpyriphos methyl, fenitrothion and fipronil) under the applied conditions. The relation between the operational parameters (viz. automatic gain control (AGC) target, maximum injection time (IT), underfill ratio, isolation window and apex trigger) and the number of automatically identified compounds was investigated. Mass error and minimal intensity of selected fragment ions were also studied. Various working modes were compared, such as full scan with single MS/MS scan and full scan with multiple MS/MS scans. In both cases, the number of automatically reported pesticides was the same. However full scan with single MS/MS scan ensured more points per peak in full scan mode and better peak area reproducibility. The evaluation of the identification and quantitation capabilities of the instrument was performed through the analysis of 100 real samples. The samples were also analysed by LC–QqQ MS/MS and the results of both analytical systems were compared. The comparison revealed that the two instruments were consistent with each other. They found the same pesticides and neither false positive nor false negatives were reported. Nevertheless the Q-Orbitrap MS allowed one to work in high resolution mass spectrometry, increasing the selectivity and, in full scan mode, permitting the retrospective analysis of the data feature that cannot be achieved with QqQ.

The evaluation of matrix effects in pesticide multi-residue methods via matrix fingerprinting using liquid chromatography electrospray high-resolution mass spectrometry

Twenty-three different commodities were extracted using the QuEChERS method. Their natural compounds were mapped based on their retention time and accurate mass using liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS). In addition, repeated analyses of spiked samples were evaluated to understand the relationship between the matrix ions and ion suppression. The number, distribution and abundance of the natural components varied greatly between the matrices, even within the same commodity group. We considered complex matrices to be those providing a high number/concentration of natural components along with high ion suppression (>50%). For example, leek contained more than 50% of pesticides with high ion suppression. Conversely, simple matrices such as tomato presented practically no pesticides (<5%) with high ion suppression. Injection amounts of 10 μL of the matrix extracts were evaluated containing 0.1 g mL−1 of matrix equivalent (or lower) instead of the common values of 1 g mL−1; this new proposed approach being an effective method to evaluate the reductions in interfering compounds and thus decreasing the problems associated with ion suppression. Finally, matrix fingerprinting studies on the accurate mass compounds obtained following the application of various extraction methods helped to determine the number and molecular weight of the co-extracted compounds, leading to the selection of the most suitable multi-residue extraction method. Such studies have evaluated the interest in the application of extraction methods and specific clean-up materials such as calcium chloride (CaCl2) in tea, or zirconium dioxide (ZrO2) in parsley analysis as a modification to the original QuEChERS method.

Evaluation of supercritical fluid chromatography coupled to tandem mass spectrometry for pesticide residues in food

Supercritical fluid chromatography coupled to triple quadrupole mass spectrometry has been evaluated for pesticide residues in food. In order to check its advantages and limitations it was developed a method to identify and quantify 164 pesticides in three different matrices (tomato, orange and leek). A carbon dioxide gradient with methanol (containing 1 mM ammonium formate) was used allowing a flow rate of 1.5 mL/min that made the total run time of 12 min without any problem of overpressure. Addition of a post column flow 150 μL/min of Methanol with ammonium formate/formic acid was necessary to improve the ionization. The matrix effect study revealed that the percentages of pesticides with irrelevant matrix effect (suppression lower than 20%) was 99% in tomato, 87% in orange and 62% in leek, whereas significant suppression (higher than 50%) was not found in tomato and only 1% of the compounds in orange and 3% in leek.These results compare favorably with that typically obtained in LC-MS/MS. The absence of water in the mobile phase, also provided some important advantages regarding LC-MS/MS as (i) higher retention of polar compounds in the column, which elute with high sensitivity and good peak shape and (ii) a general increase of the sensitivity of the analysis, consequence of the high ionization and ion extraction efficiency. Pesticides evaluated were identified following the SANTE/11813/2017. At the spiking concentration of 5 μg/kg, 98% of the pesticides were identified in tomato, 98% in orange and 94% in leek, whereas for the concentration of 10 μg/kg all the compounds were identified in tomato and only spiromesifen was not identified in orange and leek. At the concentration of 20 μg/kg, spiromesifen was also identified in these two matrices. The linearity and reproducibility of the method were evaluated with results which guarantee high quality in the analytical measurements. Even though only 2 μL of final extract were injected, the sensitivity of the SFC method was enough to achieve stringent LOQs.Real samples, including 6 different fruits and vegetables, were analyzed by the SFC-MS/MS proposed method, the results being similar to those obtained by LC-MS/MS. The method was also applied to a proficiency test of fipronil in eggs with good results in all the cases. Carbon dioxide as mobile phase with methanol as modifier can represent a good alternative to LC-MS/MS with reduction of matrix effects and shorter run times.

Coupling Ion Chromatography to Q-Orbitrap for the Fast and Robust Analysis of Anionic Pesticides in Fruits and Vegetables

Ion chromatography coupled to a quadrupole Orbitrap mass analyzer was used to develop a multiresidue method for the determination of highly polar pesticides and their metabolites (chlorate, perchlorate, fosetyl-aluminum, glyphosate, aminomethylphosphonic acid (AMPA), phosphonic acid, N-acetyl AMPA, and N-acetyl glyphosate) in fruits and vegetables. After extraction with methanol, samples were diluted 5× with water. No derivatization was applied. Pesticides were separated in an anion-exchange column. Water was used as the ion chromatography mobile phase. A gradient was created by increasing the concentration of KOH in the mobile phase. Ion chromatography provided good and stable retention and separation for all studied compounds. All investigated pesticides had an LOQ of 0.01 mg/kg and a linear range of 0.01-0.50 mg/kg. The ion ratio of the m/z ions produced was stable and adequate (deviation <30%) in all cases. The obtained mass errors (always in full-scan MS and MS2 mode) were <0.2 mDa. The high resolution (>100 000) provided by the Orbitrap analyzer with the low m/z ions obtained (e.g., m/z 80) was effective in obtaining low background matrix signals. The influence of postcolumn infusion of organic solvent on sensitivity was investigated. Acetonitrile was found to be more effective than methanol, increasing the sensitivity 3× with respect to water. The method was validated for five vegetable-based matrixes. Both the sample processing and the analytical measurement were very fast. Hence, the methodology is ideal for high-throughput work.

Sensitive Detection of Neonicotinoid Insecticides and Other Selected Pesticides in Pollen and Nectar Using Nanoflow Liquid Chromatography Orbitrap Tandem Mass Spectrometry

In this work, a new method based on nanoflow LC with high-resolution MS was developed for the determination of eight pesticides in pollen and nectar samples, including neonicotinoid insecticides and other selected pesticides commonly found in bees and beeswax. Detection was undertaken with a hybrid quadrupole-Orbitrap mass spectrometer (Q Exactive™) equipped with a commercial nanospray ion source. The extraction of pesticides from pollen samples was performed by a modified micro-QuEChERS method scaled down to Eppendorf tubes, whereas nectar samples were simply diluted with a water-methanol (95 + 5, v/v) solution. Good linearity (>0.999 in all cases) was obtained between 0.05 and 500 µg/kg and between 0.04 and 400 µg/kg for pollen and nectar, respectively. Recovery rates in pollen ranged from 85 to 97%, with RSDs <12%. Matrix effect was evaluated and showed negligible effects for all studied pesticides. The lowest concentration levels tested and validated were 0.5 and 0.4 µg/kg for pollen and nectar matrixes, respectively. In addition, selected incurred samples were studied, obtaining several positive findings in pollen and nectar samples, demonstrating the sensitivity and applicability of the proposed method.

Simultaneous combination of MS2 workflows for pesticide multiresidue analysis with LC-QOrbitrap

This study describes an evaluation of full-scan MS analysis combined with target and non-target MS2 acquisition along with targeted processing for pesticides in fruit and vegetables. Two databases were used comprising priority compounds (target acquisition) and less frequently detected compounds (non-target acquisition). Full-scan MS data were used for detection and quantitation, whereas MS2 data were used for identification. Target MS2 (data-dependent MS2) data were acquired for 166 pesticides with known retention times. Non-target MS2 (all-ion fragmentation MS2) data were obtained against a database containing 101 pesticides without retention times. At the level of 0.01 mg kg−1, selected target pesticides were identified in 99% of the cases in tomato (the best case) and in 92% of the cases in leek (the worst case). Peak area repeatability (RSD < 20%) at 0.01 mg kg−1 was satisfactory (99% of compounds in tomato and 90% in leek). In the case of non-target compounds (searched without retention times), the numbers of false-positive and false-negative results were determined. A total of seventy-two real samples were used to determine the false positives. The database search was carried out considering only the full-scan MS ion, the full-scan MS ion and one MS2 fragment, and the full-scan MS ion and two MS2 fragments. In the first case, 297 false positives were found, whereas in the second case, 7, and in the third case, 4 false positives were found. Analogical database searches were carried out for five spiked matrices to determine the false negatives. At the level of 0.01 mg kg−1, three ions (one in full-scan MS and two in MS2) were found for 96% of the compounds in tomato and lettuce (the best cases) and 75% of the compounds in leek (the worst case). Two ions (one in full-scan MS and one in MS2) were detected for 100% of the pesticides in lettuce and for 95% of the pesticides in leek. These results clearly show the high analytical performance of the applied workflow, with important advantages derived by increasing the analytical scope for qualitative screening. The approach presented in this study combines the advantages of target and non-target MS2 analysis.