Multiclass detection and quantitation of antibiotics and veterinary drugs in shrimps by fast liquid chromatography time-of-flight mass spectrometry

A fast liquid chromatography time-of-flight mass spectrometry (LC-TOFMS) method has been developed for simultaneous quantitative multiclass determination of residues of selected antibiotics and other veterinary drugs (benzalkonium chloride, ethoxyquin, leucomalachite green (LMG), malachite green (MG), mebendazole, sulfadiazine, sulfadimethoxine, sulfamethazine, sulfamethizole, sulfanilamide, sulfapyridine, sulfathiazole and trimethoprim) in shrimps. Different sample treatment methodologies were tested for the extraction of the targeted species based on either liquid partitioning with different solvents, solid-phase extraction or and matrix solid-phase dispersion. The final selected extraction method consisted of solid-liquid extraction protocol using acetonitrile as solvent followed by a clean-up step with primary secondary amine (QuEChERS). Recovery rates for the extraction of the selected multiclass chemicals were in the range 58-133%. Subsequent identification, confirmation and quantitation were carried out by LC-TOFMS analysis using a reverse-phase C₁₈ column with 1.8 μm particle size. The confirmation of the target species was based on accurate mass measurements of the protonated molecules ([M+H]⁺) and their fragment ions, obtaining routine accuracy errors lower than 2 ppm in most cases. The optimized LC-TOFMS method displayed excellent sensitivity for the studied analytes, with limits of detection (LODs) in the range 0.06-7 μg kg⁻¹. Finally, the proposed method was successfully applied to the analysis of 12 shrimp samples collected from different supermarkets, showing the potential applicability of the method for ultratrace detection of these chemicals in such complex matrix.     

Rapid determination of BTEXS in olives and olive oil by headspace-gas chromatography/mass spectrometry (HS-GC-MS)

In this work, a straightforward, reliable and effective automated method has been developed for the direct determination of monoaromatic volatile BTEXS group (namely benzene, toluene, ethylbenzene, o-, m- and p-xylenes, and styrene) in olives and olive oil, based on headspace technique. Separation, identification and quantitation were carried out by headspace-gas chromatography-mass spectrometry (HS-GC-MS) in selected ion monitoring (SIM) mode. Sample pretreatment or clean-up were not necessary (besides olives milling) because the olives and olive oil samples are put directly into an HS vial, automatically processed by HS and then injected in the GC-MS for chromatographic analysis. The chemical and instrumental variables were optimized using spiked olives and olive oil samples at 50 μg kg⁻¹ of each targeted species. The method was validated to ensure the quality of the results. The precision was satisfactory with relative standard deviations (RSD (%)) in the range 1.6-5.2% and 10.3-14.2% for olive oil and olives, respectively. Limits of detection were in the range 0.1-7.4 and 0.4-4.4 μg kg⁻¹ for olive oil and olives, respectively. Finally, the proposed method was applied to the analysis of real olives and olive oil samples, finding positives of the studied compounds, with overall BTEXS concentration levels in the range 23-332 μg kg⁻¹ and 4.2-87 μg kg⁻¹ for olive oil and olives, respectively.     

Large-scale pesticide testing in olives by liquid chromatography–electrospray tandem mass spectrometry using two sample preparation methods based on matrix solid-phase dispersion and QuEChERS

In this work we have evaluated the performance of two sample preparation methodologies for the large-scale multiresidue analysis of pesticides in olives using liquid chromatography–electrospray tandem mass spectrometry (LC–MS/MS). The tested sample treatment methodologies were: (1) liquid–liquid partitioning with acetonitrile followed by dispersive solid-phase extraction clean-up using GCB, PSA and C₁₈ sorbents (QuEChERS method – modified for fatty vegetables) and (2) matrix solid-phase dispersion (MSPD) using aminopropyl as sorbent material and a final clean-up performed in the elution step using Florisil. An LC–MS/MS method covering 104 multiclass pesticides was developed to examine the performance of these two protocols. The separation of the compounds from the olive extracts was achieved using a short C₁₈ column (50 mm × 4.6 mm i.d.) with 1.8 μm particle size. The identification and confirmation of the compounds was based on retention time matching along with the presence (and ratio) of two typical MRM transitions. Limits of detection obtained were lower than 10 μg kg⁻¹ for 89% analytes using both sample treatment protocols. Recoveries studies performed on olives samples spiked at two concentration levels (10 and 100 μg kg⁻¹) yielded average recoveries in the range 70–120% for most analytes when QuEChERS procedure is employed. When MSPD was the choice for sample extraction, recoveries obtained were in the range 50–70% for most of target compounds. The proposed methods were successfully applied to the analysis of real olives samples, revealing the presence of some of the target species in the μg kg⁻¹ range. Besides the evaluation of the sample preparation approaches, we also discuss the use of advanced software features associated to MRM method development that overcome several limitations and drawbacks associated to MS/MS methods (time segments boundaries, tedious method development/manual scheduling and acquisition limitations). This software feature recently offered by different vendors is based on an algorithm that associates retention time data for each individual MS/MS transition, so that the number of simultaneously traced transitions throughout the entire chromatographic run (dwell times and sensitivity) is maximized.     

Sample treatment and determination of pesticide residues in fatty vegetable matrices: A review

A demanding task in pesticide residue analysis is yet the development of multi-residue methods for the determination of pesticides in vegetables with relatively high fat content (i.e. edible oils and fatty vegetables). The separation of pesticides and other chemical contaminants from high-fat food samples prior to subsequent steps in the analytical process is yet a challenging issue to which much effort in method development has being applied. This review addresses the main sample treatment methodologies for pesticide residue analysis in fatty vegetable matrices. Even with the advent of advanced hyphenated techniques based on mass spectrometry these complex fatty matrices usually require extensive sample extraction and purification. Current methods involve the use of one or the combination of some of the following techniques for both the sample extraction and clean-up steps: liquid-liquid partitioning, solid-phase extraction (SPE), gel-permeation chromatography (GPC), matrix solid-phase dispersion (MSPD), etc. An overview of methods developed for these contaminants in fatty vegetables matrices is presented. Sample extraction and purification techniques are discussed and their most recent applications are highlighted. This review emphasizes that sample preparation is a critical step, but also the determination method is, and cannot be treated separately from sample treatment. In recent years, the appearance and use of new, more polar pesticides has fostered the development of liquid chromatography/mass spectrometry (LC-MS) besides gas chromatography. The main features of LC-MS for the analysis of multi-class pesticides in fatty vegetable samples will be also underlined, with an emphasis on the multi-class, multi-residue strategy and the difficulties associated.     

Determination of nitrotyrosine in Arabidopsis thaliana cell cultures with a mixed-mode solid-phase extraction cleanup followed by liquid chromatography time-of-flight mass spectrometry

In this work, a method for the determination of trace nitrotyrosine (NO₂Tyr) and tyrosine (Tyr) in Arabidopsis thaliana cell cultures is proposed. Due to the complexity of the resulting extracts after protein precipitation and enzymatic digestion and the strong electrospray signal suppression displayed in the detection of both Tyr and NO₂Tyr from raw A. thaliana cell culture extracts, a straightforward sample cleanup step was proposed. It was based on the use of mixed-mode solid-phase extraction (SPE) using MCX-type cartridges (Strata?-X-C), prior to identification and quantitation using fast liquid chromatography–electrospray time-of-flight mass spectrometry. Unambiguous confirmation of both amino acids was accomplished with accurate mass measurements (with errors lower than 2 ppm) of each protonated molecule along with a characteristic fragment ion for each species. Recovery studies were accomplished to evaluate the performance of the SPE sample preparation step obtaining average recoveries in the range 92–101 %. Limit of quantitation obtained for NO₂Tyr in A. thaliana extracts was 3 nmol L^?1. Finally, the proposed method was applied to evaluate stress conditions of the plant upon different concentrations of peroxynitrite, a protein-nitrating compound, which induces the nitration of Tyr at the nanomolar range. Detection and confirmation of the compounds demonstrated the usefulness of the proposed approach.

Impact of homogeneous and filamentary discharge modes on the efficiency of dielectric barrier discharge ionization mass spectrometry

The present study contributes to the evaluation of dielectric barrier discharge-based ambient ionization for mass spectrometric analysis (DBDI-MS) by providing a further step towards an understanding of underlying ionization processes. This examination highlights the effect of physical discharge modes on the ionization efficiency of the DBDI source. A distinction is made between the homogeneous and filamentary discharge mode due to different plasma gases in barrier configurations. Therefore, we first report on discharge modes of DBDI by demonstrating a universally applicable method to classify the predominant modes. Then, the ionization efficiency of these two modes is evaluated by a laser desorption-DBDI-MS with different molecular analytes. Here, the laser desorption is used to deliver neutral analytes which will be ionized by the plasma jet applied as dielectric barrier discharge ionization. With a clear increase of signal intensities in the homogeneous mode in contrast to the filamentary one, the present study indicates a pronounced dependence of the ionization efficiency on the discharge mode allowing further insight into the mechanisms of the ionization process.

Evaluation of two sample treatment methodologies for large-scale pesticide residue analysis in olive oil by fast liquid chromatography–electrospray mass spectrometry

In this study, a comprehensive evaluation of two simple sample treatment methodologies has been carried out for the development of large-scale multi-residue methods for pesticide testing in olive oil. The proposed methodologies are based on (a) liquid–liquid partitioning with acetonitrile followed by dispersive solid-phase extraction clean-up using graphitized carbon black, primary-secondary amine and C₁₈ sorbents; (b) liquid partitioning with acetonitrile saturated with petroleum ether followed by matrix solid-phase dispersion (MSPD) using aminopropyl as sorbent material and a Florisil cartridge for final clean-up in the elution step. To evaluate the proposed sample treatment methodologies, 105 representative multi-class pesticides were studied using fast liquid chromatography–electrospray time-of-flight mass spectrometry (LC–TOFMS). For validation purposes, recoveries studies were carried out at 10 and 100 μg kg⁻¹ levels, yielding recovery rates in the range 70–130% for 72% of analytes using liquid–liquid procedure and for 57% analytes using MSPD procedure. The LC–MS method provided good linearity, precision and accuracy. The limits of detection obtained were lower than 10 μg kg⁻¹ for more than 85% analytes using both sample treatment methodologies. In addition, minor matrix effects (i.e. signal suppression or enhancement ≤20%) were observed in ca. 70% of the studied compounds. Data obtained shows that both sample treatment methodologies proposed can be successfully applied for large-scale pesticide testing in olive oil samples, showing the ability to quickly detect trace amount of over one hundred target species with different physicochemical properties, without requiring expensive instrumentation for sample treatment step and involving relatively low amounts of solvent consumption and waste generation.     

Analyses of pesticide residues in fruit-based baby food by liquid chromatography/electrospray ionization time-of-flight mass spectrometry

A liquid chromatography/electrospray ionization time-of-flight mass spectrometry (LC/ESI-TOFMS) method has been developed for the determination of 12 pesticides (namely, carbendazim, thiabendazole, imazalil, tridemorph, triadimefon, bitertanol, prochloraz, flutriafol, myclobutanil, iprodione, diphenylamine and procymidone) in fruit-based baby food (multi-fruit jars and juices intended for infant consumption). The developed method consists of a sample treatment step based on liquid-liquid extraction using acetonitrile, followed by a clean-up step based on dispersive solid-phase extraction (SPE) with a primary-secondary amine (PSA). Multi-fruit and apple juices were processed by a SPE procedure using Oasis HLB cartridges. Subsequent identification and quantitation was accomplished by LC/ESI-TOFMS analysis: the confirmation of the target pesticides was based on accurate mass measurements of selected ions (protonated molecules ([M+H]+) and fragment ions). Confirmation studies were accomplished at low concentration levels (10 microg kg-1) and accuracy errors lower than 2 ppm were obtained in most cases. Baby food extracts spiked at 10 microg kg-1 fortification level yielded average recoveries in the range 78-105% with relative standard deviations less than 10% for most of the analytes. Limits of detection (LODs) were between 0.1 and 4 microg kg-1 depending on the pesticide studied. Finally, the proposed method was applied to a total of 33 baby food samples from Spain and the United Kingdom. Although imazalil, thiabendazole and carbendazim were detected in a high number--over 60%- of baby food samples, none of the samples tested were found to be above the 0.01 mg kg-1 EU standard.