Co-extracted Matrix Components Research Articles

Extraction and analysis of moxidectin in wombat plasma and faeces

Sarcoptic mange in wombats results from a skin infestation by Sarcoptes mites and if untreated, results in a slow and painful death. Moxidectin is a pesticide used to treat internal and external parasites in cattle, but has shown to effectively treat other animals, including wombats. Two methods were developed to analyse wombat plasma, and methods were also developed to analyse faeces and fur. Moxidectin-D3 was used as an internal standard and behaved almost identically to moxidectin, resulting in recoveries of 95–105 % across the three matrices, even when matrix interferences caused signal suppression as high 20 %, or when moxidectin loss was high. This was presumably due to the high binding efficiency of plasma for MOX and MOX-D3. Moxidectin limits of detection were 0.01 ng/mL in plasma, 0.3 ng/g dry weight equivalent for faeces and 0.5 ng/g for fur. This study also developed a method to isolate plasma macromolecules, allowing the extraction of bound moxidectin for quantitative purposes, with an LoQ of 0.05 ng/mL. This method was subsequently used to determine that moxidectin was 97–99.4 % bound to lipoproteins in wombat plasma and 98–99 % bound in sheep, cow and horse plasma. The method reported for plasma was quick, cheap, and conducive to large sample batches, while providing high sensitivity. While faecal samples required additional cleanup steps to reduce the matrix effect, co-extracted matrix components such as undigested chlorophyll continued to result in ionisation suppression in the MS/MS. The methods reported here were used to monitor moxidectin in wombats treated with a single pour-on treatment, and confirmed that the moxidectin concentration in wombat plasma had decreased by more than 90 % by 28 days after application, while providing protection against sarcoptic mites over the majority of their life cycle. Clearance of moxidectin occurred via faecal elimination over the four week period and while moxidectin accumulated on fur due to application as a pour-on, concentrations declined rapidly by the four week period as fur fell out and was replaced by fresh fur that did not contain moxidectin.

Clean-up Strategy for Dithiocarbamate Fungicide Determination in Soybean by GC-ITD-MS and GC-PFPD: Method Development and Validation.

Food matrices consist of many components with different physical and chemical properties that may influence instrumental robustness. The soybean contains fatty coextractives which may have a deleterious effect on the gas chromatography (GC) system. In this study, the efficiencies of PSA, C18OH, C18, silica, aluminum oxide, and Florisil, as dSPE clean-up sorbents, were evaluated by the high-performance liquid chromatography (HPLC) diode-array detector and evaporative light-scattering detector analysis. The dithiocarbamates in soybean samples are determined as CS2 using acidic hydrolysis and isooctane partitioning, followed by GC-PFPD and GC-ITD-MS analyses. The linearity of the analytical curves, the instrument limit of detection matrix effects, the trueness and precision, and the method limit of quantification (LOQ) were assessed in the validation study. Milled soybean was spiked with thiram solution at three concentration levels (corresponding to 0.05, 0.1, and 0.5 mg CS2 kg-1) for recovery determination. Silica appeared to be an effective and cheap sorbent to remove coextracted matrix components without causing any CS2 losses. Recoveries were in the range of 68-91%, with relative standard deviations ≤ 8.7%. The method LOQ was 0.05 mg CS2 kg-1, and both GC-ITD-MS and GC-PFPD systems appeared to be appropriate and complementary to determine dithiocarbamate residues in soybean extracts.

Combustion ion chromatography for extractable organofluorine analysis

SummaryCombustion ion chromatography (CIC) has found a role in environmental analytical chemistry for fluorine content analysis. It is used for extractable organofluorine (EOF) analysis to evaluate perfluoroalkyl and polyfluoroalkyl substances (PFASs) and other organofluorine burden. The prevailing assumption has been that all PFASs are incinerated in CIC and matrix components have no impact on this process, but this has not been experimentally evaluated. In this work, the combustion efficiencies of 13 different PFASs were determined (66–110%). A notable difference was observed between calibrating the CIC with inorganic fluorine or organofluorine. Potential interferences from cations and coextracted matrix components from whole blood and surface water samples were evaluated. These observations should be acknowledged when performing EOF analysis using CIC, overlooking either non-100% combustion efficiencies or the differences in calibrating the CIC with inorganic fluorine or organofluorine could lead to underestimating EOF content and through that to misguide policy decisions.

LC-QTOF/MS determination of tryptophan and kynurenine in infant formulas

A rapid, reliable and sensitive liquid chromatography quadrupole time-of-flight mass spectrometry method for the determination of tryptophan and its metabolite kynurenine in milk formulas for neonates and infants was developed and validated. Two extraction techniques based on EMR Lipid QuEChERS and liquid-liquid extraction with diethyl ether to extract lipids and methanol to precipitate the protein were tested and compared. Four different infant formula products were randomly selected and evaluated for the effect of co-extracted matrix components on the quantitative analysis results. The influence of matrix components on analytical signals was normalized by the use of stable isotope-labeled standards and matrix-matched calibration. The developed method was found to be sensitive and effective for both analytes in all the examined infant formulas with satisfactory linearity (R2 ≥ 0.9995), recovery in the range of 75.7% ± 4.5 – 99.0% ± 1.1, and intra- and inter-day precision with the coefficient of variation below 6.3% and 17.9%, respectively. The limits of detection (LOD) and quantification (LOQ) for both compounds differed significantly between the examined formulas. The LOD and LOQ values were found to be in the range of 2.18–9.85 μg/g and 6.61–29.84 μg/g for the determination of tryptophan and in the range of 0.21–2.71 μg/g and 0.63–8.23 μg/g for the determination of kynurenine, respectively. The method was proved to be suitable for the determination of tryptophan and kynurenine in infant formulas, and it can be used to study the link between tryptophan metabolism via kynurenine pathway and metabolic disorders in infants.

Direct sample introduction GC-MS/MS for quantification of organic chemicals in mammalian tissues and blood extracted with polymers without clean-up

Solvent extracts of mammalian tissues and blood contain a large amount of co-extracted matrix components, in particular lipids, which can adversely affect instrumental analysis. Clean-up typically degrades non-persistent chemicals. Alternatively, passive sampling with the polymer polydimethylsiloxane (PDMS) has been used for a comprehensive extraction from tissue without altering the mixture composition. Despite a smaller fraction of matrix being co-extracted by PDMS than by solvent extraction, direct analysis of PDMS extracts was only possible with direct sample introduction (DSI) GC-MS/MS, which prevented co-extracted matrix components entering the system. Limits of quantitation (LOQ) ranged from 4 to 20 pg μL−1 ethyl acetate (PDMS extract) for pesticides and persistent organic pollutants (POPs). The group of organophosphorus flame retardants showed higher LOQs up to 107 pg μL−1 due to sorption to active sites at the injection system. Intraday precision ranged between 1 and 10%, while the range of interday precision was between 1 and 18% depending on the analyte. The method was developed using pork liver, brain, and fat as well as blood and was then applied to analyze human post-mortem tissues where polychlorinated biphenyls (PCBs) as well as dichlorodiphenyltrichloroethane (DDT) and DDT metabolites were detected.Graphical abstract

Dilute-and-Shoot Liquid Chromatography Approach for Simple and High-throughput Analysis of 5-Hydroxymethylfurfural in Fruit-based Baby Foods

The present work focuses on a cost-effective and environment-friendly approach for the determination of 5-hydroxymethylfurfural (HMF) in baby foods, a process-induced food compound of toxicological interest. The proposed method includes acetonitrile-based extraction followed by dilution of the extract with water in order to minimize the interference from other co-extracted matrix components and eliminate the demand for further clean-up procedure, and then high-performance liquid chromatography analysis with diode array detection (HPLC-DAD). Adequate performance characteristics were achieved including limits of detection and quantification of 0.02 and 0.04 μg g−1, respectively; recoveries from 98 to 102% and precision (RSD values ≤ 4%) under repeatability and within-laboratory reproducibility conditions. The application of the validated method to commercial fruit-based baby foods and the detection of HMF in all samples (contents between 2.3 and 195.4 μg g−1) demonstrated their suitability for baby food control as well as it contributed to the first data on HMF in fruit-based baby foods available in the Brazilian market.

Multiclass Multipesticide Residue Analysis in Fish Matrix by a Modified QuEChERS Method Using Gas Chromatography with Mass Spectrometric Determination.

Pesticide residue in fish is a global food safety concern. However, very few validated methods are available targeting simultaneous analysis of multiple classes of pesticides. The aim of this study was to validate a quick, easy, cheap, effective, rugged, and safe workflow-based method for the quantitative determination of multiclass pesticides in fish matrix using GC-MS determination. The sample was extracted with acetonitrile, and the cleanup method involved dispersive solid-phase extraction with C-18 sorbent, which effectively scavenged the coextracted matrix components and removed those from the extract. The data on recovery and precision of the method satisfied the criteria of SANTE/11813/2017 guidelines. Average recoveries of pesticides were in the range of 80-120% with precision RSDs ≤20%. The LOD and LOQ were in the ranges of 0.001-0.029 and 0.005-0.125 µg/mL, respectively, for all pesticides. The expanded uncertainty was in the range of 14-20%, based on the single-laboratory validation data (coverage factor, k = 2, confidence level, 95%). The validation data prove that the method is convenient and acceptable for the routine analysis of multiclass pesticide residues in fish matrices for regulatory compliance. The study achieves multiresidue analysis of pesticides in fish matrix with MS-based confirmation. The method combines the advantages of nontarget analysis based on National Institute of Standards and Technology library matching in full scan mode with selected-ion monitoring-based sensitivity.

Improved determination of femtogram-level organic explosives in multiple matrices using dual-sorbent solid phase extraction and liquid chromatography-high resolution accurate mass spectrometry

Identification and trace quantification of multiple explosives residues, their precursors and transformation products in complex samples remains very challenging. For solid phase extraction (SPE) and liquid chromatography-high resolution accurate mass spectrometry-based methods (LC-HRMS), interferences from co-extracted matrix components can significantly affect recovery during extraction and/or detector signal. The aim of this work was to develop a new, improved and more generalisable extraction approach to trace explosives analysis in a range of matrices using dual-sorbent SPE with LC-HRMS. Recoveries of 44 organic explosives from model solutions were optimised and compared for seven different sorbents (Oasis HLB, HyperSep Retain PEP and Isolute ENV+, HyperSep SAX, HyperSep NH2, Strata Alumina-N and Bond Elut CN). On average, Oasis HLB and Isolute ENV+ yielded the best recoveries (>80%). For three sorbents, mean recoveries remained ≤1%, which made them potentially suitable for matrix removal when used in series with more analyte-selective sorbents. To evaluate matrix effects, a range of aqueous (river- and wastewater), solid (soil), dirty (road sign swabs), oily (oven hood swabs) and biological (dried blood) samples were selected based on complexity and forensic relevance. With the exception of river water, matrix effects were lowest using dual-sorbent SPE, with little/no compromise in recovery. Quantitative method performance assessment is presented for 14 selected explosives, representative of different classes, molecular weights and volatilities, and across three different matrices (i.e. untreated wastewater, cooking oil residues and dried blood). Limits of detection improved by ∼10-fold over a single sorbent approach, enabling low fg sensitivity in many cases. Finally, application of the method to untreated wastewater enabled detection of new explosives traces for the first time, which could be used to help identify clandestine manufacture or sources of environmental toxicity. This approach offered a versatile solution to sample preparation for robust and highly sensitive detection/quantification of large numbers of explosives residues in a range of complex sample types.

Development of an efficient method for multi residue analysis of 160 pesticides in herbal plant by ethyl acetate hexane mixture with direct injection to GC-MS/MS

A simple and efficient multi residue method was developed, for the analysis of 160 pesticides by GC-MS/MS in herbal plants. The developed method employs pesticide residue extraction by EtAC/ n. hexane (6:4) with a cleanup step using florisil/ PSA mixture. The optimized conditions have resulted in lower co-extracted matrix components than those extracted using EtAC or MeCN (QuEChERS method), according to FTIR and full scan GC/MS analyses. In addition, the developed method (EtAC/ Hexane) eliminates the evaporation step that is usually performed when using MeCN as an extraction solvent prior to the GC-MS/MS injection. The developed method was fully validated on chamomile, based on SANTE/11945/2015 guidelines. Where, intraday recoveries were estimated at three concentration levels of 10, 50 and 250μgkg−1. However, interday recoveries have also been carried out, at 250μgkg−1. In addition, intraday recoveries were estimated for two other herbal plants (thyme and marjoram), at 250μgkg−1. Three point calibration mixtures were prepared in ethyl acetate solvent and in the blank extracts of chamomile, thyme, and marjoram, in order to check the linearity and matrix effect. The average recoveries for most of the studied pesticides ranged from 70% to 100% at 50 and 250μgkg−1 with relative standard deviations below 20%. The validated method was successfully applied for determination of pesticide residues in 20 herb samples, collected from the Egyptian market.

Determination of Rodenticide Tetramethylenedisulfotetramine (Tetramine) in Processed Foods by Gas Chromatography-Tandem Mass Spectrometry.

A GC-MS/MS method for determination of the rodenticide tetramethylenedisulfotetramine was developed. Tetramethylenedisulfotetramine was extracted from the sample with ethyl acetate in the presence of anhydrous sodium sulfate. Then, an aliquot of the extract was evaporated under vacuum, followed by acetonitrile/hexane partitioning, and cleanup with a tandem graphitized carbon/primary secondary amine (PSA) column, prior to GC-MS/MS analysis. The recoveries from 10 processed foods, all of which were fortified at 0.1 mg/kg, were in the range of 85-96%, and the relative standard deviations were less than 7%. The proposed method effectively removed co-extracted matrix components, and matrix effects were negligible in the GC-MS/MS analysis. In addition, no interfering peaks were found in the chromatograms of the blank samples at the retention time of tetramethylenedisulfotetramine, indicating that the method is highly selective. Overall results suggest that the proposed method is suitable for determining tetramethylenedisulfotetramine contained in processed foods.

Multiresidue determination of pesticides in tea by gas chromatography-tandem mass spectrometry

An efficient and reliable GC-MS/MS method for the multiresidue determination of pesticides in tea was developed by modifying the Japanese official multiresidue method. Sample preparation was carefully optimized for the efficient removal of coextracted matrix components. The optimal sample preparation procedure involved swelling of the sample in water; extraction with acetonitrile; removal of water by salting-out; and sequential cleanup by ODS, graphitized carbon black/primary secondary amine (GCB/PSA) and silica gel cartridges prior to GC-MS/MS analysis. The recoveries of 162 pesticides from fortified (at 0.01 mg kg−1) green tea, oolong tea, black tea and matcha (powdered green tea) were mostly (95–98% of the tested pesticides) within the range of 70–120%, with relative standard deviations of <20%. Poor recovery of triazole pesticides was considered to be due to low recovery from the silica gel cartridges. The test solutions obtained by the modified method contained relatively small amounts of pigments, caffeine and other matrix components and were cleaner than those obtained by the original Japanese official multiresidue method. No interfering peaks were observed in the blank chromatograms, indicating the high selectivity of the modified method. The overall results suggest that the developed method is suitable for the quantitative analysis of GC-amenable pesticide residues in tea.

Simultaneous determination of acidic pesticides in vegetables and fruits by liquid chromatography—tandem mass spectrometry

A sensitive and efficient method has been developed for the simultaneous determination of 73 multi-class acidic pesticides, such as phenoxy acid and sulfonylurea herbicides, in vegetables and fruits. The sample preparation procedure was carefully optimized for the efficient removal of co-extracted matrix components. The method involves extraction of acidic pesticides with acetonitrile containing hydrochloric acid, removal of water from crude extract by salting out, and sequential cleanup by octadecylsilyl silica gel and silica gel columns. For samples containing high amounts of pigments, such as spinach, additional cleanup using a graphitized carbon column was performed prior to liquid chromatography–mass spectrometry (LC–MS/MS) analysis. Recovery tests were performed for five times for each sample of cabbage, spinach, potato, eggplant, orange, and apple fortified at 0.01 mg kg−1. Out of the 73 tested pesticides, 70 for cabbage, 67 for spinach, 69 for potato, 67 for eggplant, 64 for orange, and 70 for apple were within the range of 70–120%, with relative standard deviations below 25%. Nitenpyram and pyrasulfotole showed low recoveries for all the samples tested, probably due to low recoveries from silica gel column. The developed method effectively removed co-extracted matrix components and was highly selective, with no interfering peaks found in the chromatograms of blank samples. The overall results indicate that the developed method is suitable for the quantitative analysis of acidic pesticide residues in vegetables and fruits.

A simple method for the determination of bisphenol A diglycidyl ether and its derivatives in canned fish

A simple extraction method was developed to determine bisphenol A diglycidyl ether (BADGE) and its derivatives in canned fish. High-performance liquid chromatography (HPLC) with fluorescence detection was employed to measure these substances. The QuEChERS method was investigated to seek out a fast, cheap and easy technique for sample preparation. The sorbent, such as primary secondary amine (PSA) or octadecylsilane (C18), was applied in the clean-up step, but it did not demonstrate any advantages to the peak shape compared with extraction without the sorbent. The sample preparation method was optimized using different extraction solvents and salts in order to reduce co-extracted matrix components and improve phase separation. The extraction results from the QuEChERS method were not the best obtained by using recovery comparison; therefore, the final sample preparation method was the use of acetonitrile with the addition of sodium chloride only. The extraction method was evaluated by using fortified samples at three concentration levels (0.10, 9.00 and 18.0 mg kg−1); extraction recoveries were in the range of 95 to 99%, with good repeatability (%RSD ≤ 9). Detection limits and quantitation limits were 0.01–0.02 and 0.03–0.05 mg kg−1, respectively. To compensate for the matrix effect, the matrix-matched calibrations were prepared and an excellent regression (r2 ≥ 0.997) was obtained. This study demonstrated a suitable extraction method for the determination of BADGE and its derivatives, with less labor, time and solvent consumption. The final method was also applied to real samples collected from local markets and the concentrations were found in legal limits.

Storage of Oral Fluid as Dried Spots on Alginate and Chitosan Foam – A New Concept for Oral Fluid Collection

In recent years, there has been a major focus on analyzing drug substances from dried µl volumes of biological fluids, commonly known as dried matrix spotting. 10 µl oral fluid, spiked with five basic drugs, was collected and stored as dried spots on alginate and chitosan foam, and subsequently dissolved; the drugs were thereafter isolated with electromembrane extraction and analyzed by LC-MS. The correlation coefficients were above 0.9885 for all drugs in the range 25-1000 ng/ml. The reported RSD values were below 15%. Storage of oral fluid as dried spots on alginate and chitosan foam have been investigated for the first time. The extract obtained after electromembrane extraction was directly compatible with LC-MS, and apparently free from coextracted matrix components.

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.

Comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry for the identification of organobrominated compounds in bluefin tuna

This study evaluates comprehensive two-dimensional gas chromatography (GC × GC) coupled to time-of-flight mass spectrometry (GC × GC–ToF MS) for the simultaneous analysis of several classes of organobromines (OBs), including polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), methoxylated PBDEs (MeO-PBDEs), several halogenated naturally produced compounds (HNPs) and eight novel brominated flame retardants (NBFRs), polybrominated hexahydroxanthene derivates (PBHDs), 2,4,6-tribromoanisole and a mixed halogenated compound (MHC-1), in bluefin tuna muscles. The proposed methodology maximised separation of both within and among OB families, and among these and other halogenated micropollutants detected in these samples and co-extracted matrix components. Special attention has been paid to solve co-elution problems observed during the analysis of OBs with one-dimensional GC-based techniques. Satisfactory separation among several relevant PBDEs and MeO-PBDEs has been obtained allowing their unambiguous determination in a single run. Additional studies were conducted to identify selected NBFRs and HNPs. 2,4-Dibromoanisole, a dibromophenol isomer and hexabromobenzene were identified in the investigated samples. Several new tri- and tetra-BHD derivates were also identified, indicating that these compounds could apparently exist as structured families in nature. In addition, a tetrabrominated diMeO-biphenyl and two tetrabrominated diMeO-BDEs were also tentatively identified.

Complexity and pitfalls of mass spectrometry-based targeted metabolomics in brain research

Current quantitative metabolomic research in brain tissue is challenged by several analytical issues. To compare data of metabolite pattern, ratios of individual metabolite concentrations and composed classifiers characterizing a distinct state, standardized workup conditions, and extraction medium are crucial. Differences in physicochemical properties of individual compounds and compound classes such as polarity determine extraction yields and, thus, ratios of compounds with varying properties. Also, variations in suppressive effects related to coextracted matrix components affect standards or references and their concentration-dependent responses.The selection of a common tissue extraction protocol is an ill-posed problem because it can be regarded as a multiple objective decision depending on factors such as sample handling practicability, measurement precision, control of matrix effects, and relevance of the chemical assay. This study systematically evaluates the impact of extraction solvents and the impact of the complex brain tissue on measured metabolite levels, taking into account ionization efficiency as well as challenges encountered in the trace-level quantification of the analytes in brain matrices. In comparison with previous studies that relied on nontargeted platforms, consequently emphasizing the global behavior of the metabolomic fingerprint, here we focus on several series of metabolites spanning over extensive polarity, concentration, and molecular mass ranges.

LC-MS/MS Quantitation of Hop-Derived Bitter Compounds in Beer Using the ECHO Technique

A new quantification method for hop-derived bitter compounds in beer was developed. By means of LC-MS/MS operating in the multiple reaction monitoring mode, a total of 26 hop-derived bitter compounds, namely, the post-, co-, n-, ad-, pre-, and adpre-congeners of iso-alpha-acids, alpha-acids, and beta-acids, as well as the prenylflavonoid isoxanthohumol and the chalcone xanthohumol, could be simultaneously detected for the first time in a single HPLC run in authentic beer samples without any cleanup procedures. To compensate for the effect of coextracted matrix components in LC-MS/MS analysis, the so-called ECHO technique was applied for the first time as a suitable strategy for the quantitative analysis of the hop-derived bitter compounds in fresh and stored beer. On the basis of quantitative data, the remarkable instability of alpha-acids and trans-iso-alpha-acids was confirmed, and it was observed that the degradation of trans-iso-alpha-acids during the storage of beer is not dependent from the nature of the alkanoyl side chain of the congeners. In contrast, an increase of the concentrations of beta-acids and of the prenylflavonoid isoxanthohumol as well as of the chalcone xanthohumol during the storage of beer was observed.

Mycotoxin analysis: An update

Mycotoxin contamination of cereals and related products used for feed can cause intoxication, especially in farm animals. Therefore, efficient analytical tools for the qualitative and quantitative analysis of toxic fungal metabolites in feed are required. Current methods usually include an extraction step, a clean-up step to reduce or eliminate unwanted co-extracted matrix components and a separation step with suitably specific detection ability. Quantitative methods of analysis for most mycotoxins use immunoaffinity clean-up with high-performance liquid chromatography (HPLC) separation in combination with UV and/or fluorescence detection. Screening of samples contaminated with mycotoxins is frequently performed by thin layer chromatography (TLC), which yields qualitative or semi-quantitative results. Nowadays, enzyme-linked immunosorbent assays (ELISA) are often used for rapid screening. A number of promising methods, such as fluorescence polarization immunoassays, dipsticks, and even newer methods such as biosensors and non-invasive techniques based on infrared spectroscopy, have shown great potential for mycotoxin analysis. Currently, there is a strong trend towards the use of multi-mycotoxin methods for the simultaneous analysis of several of the important Fusarium mycotoxins, which is best achieved by LC–MS/MS (liquid chromatography with tandem mass spectrometry). This review focuses on recent developments in the determination of mycotoxins with a special emphasis on LC–MS/MS and emerging rapid methods.

Alternative calibration approaches to compensate the effect of co-extracted matrix components in liquid chromatography–electrospray ionisation tandem mass spectrometry analysis of pesticide residues in plant materials

The aim of this study was to evaluate the applicability of different calibration approaches in a multi- and single-residue analysis of modern pesticides in plant matrices using liquid chromatography–electrospray mass spectrometry (HPLC–ESI-MS). In the first set of experiments the determination of eight pesticides representing different groups of polar/unstable pesticides (carbamates, benzimidazoles, azoles, benzoylphenylurea) in apple samples was performed. The trueness and precision of data obtained by using: (i) external solvent standard calibration, (ii) external matrix-matched standard calibration and (iii) echo-peak internal standard calibration was compared. The last mentioned method is a novel technique providing the possibility to inject internal standard of the same identity as a target analyte, so that its retention time is close to the analyte from the sample. According to expectation, when using external standard solvent calibration the results were under- or overestimated due to suppression or enhancement of analyte’s signal by matrix components. On the other hand with the use of matrix-matched calibration accurate data were obtained. With echo-peak technique accurate results comparable to those obtained by matrix calibration were obtained for six out of eight pesticides. In the second set of experiment we used the echo-peak technique to overcome the problem with the response instability in the analysis of chlormequat in pear concentrate samples. As an internal standard method the echo-peak technique provided the possibility of monitoring of signal decrease during the analytical sequence and to compensate this decrease by relating sample peak area relatively to this internal standard.