Special Issue "Applications of Stable Isotope Analysis".

The isotopic composition of matter is controlled by different physical, chemical, and biological mechanisms [...].

Quality assessment of environmental water by a simple and fast non-ionic hydrophobic natural deep eutectic solvent-based extraction procedure combined with liquid chromatography tandem mass spectrometry for the determination of plastic migrants.

A non-ionic hydrophobic natural deep eutectic solvent (HNADES) based on thymol and menthol was proposed for the liquid-liquid microextraction of fourteen phthalates and one adipate from environmental water samples. Separation, identification, and quantification were achieved by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry. The main factors affecting the extraction efficiency were thoroughly studied. Sample pH of 8 and 100 µL of thymol:menthol at molar ratio 2:1 were selected as the best conditions, while ionic strength and type of dispersant solvent were not relevant for the extraction of the target compounds. The whole methodology was validated for treated wastewater, runoff, and pond water matrices, using di-n-butyl phthalate-3,4,5,6-d4 and dihexyl phthalate-3,4,5,6-d4 as surrogates. Recovery ranged from 70 to 127% with relative standard deviation values lower than 14%. Limits of quantification of the method were in the range 0.042-0.425 µg/L for treated wastewater, 0.015-0.386 µg/L for runoff, and 0.013-0.376 µg/L for pond water. The methodology was applied for the analysis of real treated wastewater, runoff, and pond water samples from different places of Tenerife and Gran Canaria (Canary Islands) finding the presence of diethyl phthalate, diallyl phthalate, dipropyl phthalate, benzylbutyl phthalate, di-n-butyl phthalate, bis-(2-n-butoxyethyl) phthalate, di-n-pentyl phthalate, dicyclohexyl phthalate, and bis-(2-ethylhexyl) phthalate at concentrations between 105.2 and 3414 ng/L.

Investigating Hydrogen Isotope Variation during Heating of n-Alkanes under Limited Oxygen Conditions: Implications for Palaeoclimate Reconstruction in Archaeological Settings.

This paper reports on a series of heating experiments that focus on n-alkanes extracted from leaf, bark, and xylem tissues of the Celtis australis plant. These lipid biomarkers were analysed for their compound-specific hydrogen isotopic composition (δ2Hwax) under limited oxygen conditions at 150, 250, 350, and 450 °C. Our results reveal isotopic variations in wax lipids of different plant organs during short-term low-temperature combustion. We conclude that, in the absence of a detailed characterisation of the depositional environment in advance of sampling, δ2Hwax values in archaeological or otherwise highly anthropogenic environments should be interpreted cautiously. In addition, we observed that variation in δ2Hwax of leaves is minimal at temperatures ≤ 350 °C, highlighting the potential for δ2Hwax in thermally altered combustion substrates to yield palaeoclimate information, which could allow researchers to investigate links between archaeological and climatic records at a high spatial and temporal resolution.

Application of a Liquid-Liquid Microextraction Method Based on a Natural Hydrophobic Deep Eutectic Solvent for the Extraction of Plastic Migrants from Kombuchas.

A vortex-assisted liquid-liquid microextraction, based on a natural hydrophobic deep eutectic solvent made from the monoterpene thymol and octanoic fatty acid, was employed for the analysis of 11 phthalate esters and one adipate in kombucha (a tea-based fermented beverage). Separation and determination were performed using an ultra-high performance liquid chromatography (UHPLC) system coupled to a single quadrupole mass spectrometer. Confirmatory analyses were carried out through UHPLC tandem mass spectrometry. The full method was validated in terms of matrix effect, matrix-matched calibration, sensitivity, recovery, limits of detection and quantification and repeatability. Satisfactory determination coefficients for quadratic calibration curves (≥0.9938), recovery values (67-120%) and limits of detection (0.07-5.45 µg/L) were obtained. Analysis of 26 kombucha samples reported concentrations for dibutyl phthalate and dimethyl phthalate in the range between the limit of quantification (LOQ) and 16.18 ± 1.14 µg/L, although these phthalates were also detected under the LOQ in some of the analyzed samples. Only one of the samples bottled in plastic containers (7) did not present residues while only five of the 19 samples in glass bottles contained any plasticizer. However, the highest concentration was found in a kombucha bottled in food-grade glass. This work represents the first application in which phthalates and adipates are analyzed in kombuchas.

Multiresidue analysis of oestrogenic compounds in cow, goat, sheep and human milk using core-shell polydopamine coated magnetic nanoparticles as extraction sorbent in micro-dispersive solid-phase extraction followed by ultra-high-performance liquid chromatography tandem mass spectrometry.

In this work, the suitability of Fe3O4 nanoparticles coated with polydopamine was evaluated as sorbent for the extraction of a group of 21 compounds with oestrogenic activity including seven phytoestrogens, six mycotoxins as well as four synthetic and four natural oestrogens from different types of milk, including sheep milk, in which the evaluation of oestrogenic compounds have never been developed before. Extraction was carried out using magnetic micro-dispersive solid-phase extraction after a previous deproteinisation step. Separation, determination and quantification of the target analytes were achieved by ultra-high-performance liquid chromatography coupled to triple quadrupole-tandem mass spectrometry. The methodology was validated for five milk samples using 17ß-estradiol-2,4,16,16,17-d5 as internal standard for natural and synthetic oestrogens, ß-zearalanol-10,10,11,12,12-d5 for mycotoxins and prunetin for phytoestrogens. Recovery values ranged from 70 to 120% for the five types of matrices with relative standard deviation values lower than 18%. Limits of quantification of the method were in the range 0.55-11.8 µg L-1 for all samples. Graphical abstract General scheme of the multiresidue analysis of oestrogenic compounds in milk using core-shell polydopamine coated magnetic nanoparticles as extraction sorbent in µ-dSPE.

Determination of phthalic acid esters in different baby food samples by gas chromatography tandem mass spectrometry.

In this work, a new method has been developed for the determination of 14 phthalic acid esters (i.e., benzylbutyl phthalate (BBP), bis-2-n-butoxyethyl phthalate (DBEP), dibutyl phthalate (DBP), dicyclohexyl phthalate (DCHP), bis-2-ethoxyethyl phthalate (DEEP), diethyl phthalate (DEP), diisodecyl phthalate (DIDP), diisononyl phthalate (DINP), bis-isopentyl phthalate (DIPP), bis (2-methoxyethyl) phthalate (DMEP), dimethyl phthalate (DMP), di-n-octyl phthalate (DNOP), bis-n-pentyl phthalate (DNPP), dipropyl phthalate (DPP)) and one adipate (bis (2-ethylhexyl) adipate (DEHA)) in different baby foods. Separation was carried out by gas chromatography triple quadrupole tandem mass spectrometry while the previous extraction of the samples was carried out using the QuEChERS method. The methodology was validated for four baby food samples (two fruit compotes of different compositions and two meat and fish purees with vegetables) using dibutyl phthalate-3,4,5,6-d4 (DBP-d4) as internal standard. Determination coefficients (R2) of matrix-matched calibration curves were above 0.9922 in all cases while relative recovery values ranged between 70 and 120%, with relative standard deviation values below 19%. The limits of quantification of the method ranged between 0.03 and 1.11 µg/kg. Finally, the analysis of commercially available samples was carried out finding the presence of BBP, DEHA, DEP, DIDP, and DPP in some of the studied samples.

Addition of docosahexaenoic acid, but not arachidonic acid, activates glutathione and thioredoxin antioxidant systems in murine hippocampal HT22 cells: potential implications in neuroprotection.

Docosahexaenoic acid (DHA, 22:6n-3) is a major constituent of nerve cell membrane phospholipids. Besides a role in membrane architecture, DHA is a pleiotropic molecule involved in multiple facets of neuronal biology and also in neuroprotection. We show here that supplementation with DHA (but not arachidonic acid) to mouse hippocampal HT22 cells modulates the expression of genes encoding for antioxidant proteins associated with thioredoxin/peroxiredoxin and glutathione/glutaredoxin systems. Thus, within the thioredoxin system, DHA increased Txn1-2, Trxrd1-2, Prdx3, and Srxn1 gene expression. Paralleling these changes, DHA increased thioredoxin reductase activity, the main enzyme involved in thioredoxin regeneration. For the glutathione system, the most important change triggered by DHA was the upregulation of Gpx4 gene, encoding for the nuclear, cytosolic and mitochondrial isoforms of phospholipid-hydroperoxide glutathione peroxidase (PH-GPx/GPx4, the main enzyme protecting cell membranes against lipid peroxidation), which was followed by a significant increase in total glutathione peroxidase and GPx4 activities. Noticeably, DHA also upregulated a new Gpx4 splicing variant that retained part of the first intronic region. Finally, we demonstrate that DHA treatment, under the same time course, protects HT22 cells from the oxitoxic exposure to amyloid beta (Aß25-35 ) peptide. Altogether, our data pinpoint to a role of DHA as Indirect Antioxidant that modulates neuronal defences in neuroprotection. DHA improves the antioxidant capacity of cultured hippocampal HT22 cells. We propose that DHA supplementation induces the remodelling of membrane phospholipids, and also triggers a transcriptional program to increase the expression of members of the glutathione and thioredoxin systems. We postulate that this transcriptional effect is mediated by a signal arising from non-enzymatic oxidation of DHA.

Determination of estrogens in environmental water samples using 1,3-dipentylimidazolium hexafluorophosphate ionic liquid as extraction solvent in dispersive liquid-liquid microextraction.

In this work, the potential of a symmetric dialkyl-substituted ionic liquid (IL), 1,3-dipenthylimidazolium hexafluorophosphate ([PPIm][PF6 ]), as extraction solvent in dispersive liquid-liquid microextraction (DLLME) has been studied for the analysis of a group of three natural (estriol, 17ß-estradiol, and 17α-estradiol) and four synthetic (17α-ethynylestradiol, diethylstibestrol, dienestrol, and hexestrol) estrogenic compounds as well as one mycotoxin with estrogenic activity (zearalenone) in different types of water samples (Milli-Q, mineral, and wastewater). Separation, determination, and quantification were developed by HPLC-DAD and a fluorescence detector (FD) connected in series. Factors influencing the IL-DLLME procedure (sample pH, amount of IL, type and volume of disperser solvent, ionic strength, and assistance of vortex agitation) were investigated and optimized by means of a step-by-step approach. Once the optimum extraction conditions were established (10 mL of water at pH 8, 60 mg of [PPIm][PF6 ], 500 µL of ACN as disperser solvent and vortex agitation for 1 min), the calibration curves of the whole method (IL-DLLME-HPLC-DAD/FD) were obtained and precision and accuracy were evaluated. It was demonstrated that the developed methodology was repeatable, accurate, and selective with limits of detection in the 0.30-0.57 µg/L and 13.8-37.1 µg/L range for FD and DAD, respectively. Relative recovery values were higher than 85% for the different types of water samples and the Student's t test demonstrated that there were not significant differences between the added and the found concentration.

Fecal biomarkers and micromorphological indicators of sheep penning and flooring at La Fortaleza pre-Hispanic site (Gran Canaria, Canary Islands).

This study explores the lipid content and micromorphological features of sediment samples from two dwelling structures at the pre-Hispanic site of La Fortaleza in Santa Lucía de Tirajana (Gran Canaria, Spain). Previous field identification of possible sedimentary excrements inside the dwellings motivated chromatographic fecal biomarker analysis and micromorphology. The micromorphological samples reveal a complex dung-rich stratified sequence involving different layers of mixed composition, including reworked dung, clay, wood ash, and domestic refuse. The results of the lipid analysis corroborate the fecal nature of the sample and indicate the source animal: sheep. Coupled with the field evidence, the data suggest that the deposit is anthropogenic and represents a sequence of floor foundations, dung floors, and domestic and architectural refuse. This study provides valuable taxonomic and site use data for the understanding of the aboriginal societies of the Canary Islands and shows the efficacy of combining field observations with high-resolution geoarchaeological methods.

Microstratigraphic, lipid biomarker and stable isotope study of a middle Palaeolithic combustion feature from Axlor, Spain.

Archaeological research has increasingly focused on studying combustion features as valuable sources of information regarding past technological and cultural aspects. The use of microstratigraphic and biomolecular techniques enables the identification of combustion residues and substrate components, and infer about past fire-related activities and the environments. Our study conducted on a combustion feature (Level N, ∼100 Ka) at the Axlor cave, a Middle Paleolithic site in northern Iberia, exemplifies the interdisciplinary approach to combustion features. Micromorphological features revealed depositional activities associated with occupations such as hearth rake-out and trampling. Through molecular (n-alkanes, n-alcohols, and n-fatty acids) and isotopic analysis (δ13C16:0 and δ13C18:0), we infer the good preservation of organic matter, the contributions of non-ruminant fats, and the dead-wood gathering strategies by Neanderthal groups. By combining microstratigraphic and biomolecular approaches, our study significantly contributes to the advancement of our current understanding of Neanderthal pyrotechnology.

Analysis of pesticides residues in environmental water samples using multiwalled carbon nanotubes dispersive solid-phase extraction.

In this manuscript, a dispersive SPE method based on the use of multiwalled carbon nanotubes has been developed for the determination of 15 organophosphorus pesticides residues including some of their metabolites (disulfoton sulfoxide, ethoprophos, cadusafos, dimethoate, terbufos, disulfoton, chlorpyrifos-methyl, malaoxon, fenitrothion, pirimiphos-methyl, malathion, chlorpyrifos, terbufos sulfone, disulfoton sulfone, and fensulfothion) from real environmental waters (run-off, mineral and tap water) by GC with nitrogen phosphorus detection. Factors that affect the enrichment efficiency such as sample volume, multiwalled carbon nanotubes amount, and volume of eluent were studied. The optimized method was validated in terms of matrix-matched calibration, recovery, precision, and accuracy for the three analyzed samples. In this last case, the developed Student's t test demonstrated that there were no significant differences between real and spiked concentrations. Optimum dispersive SPE conditions (extraction of 200 mL of water, pH 6.0, with 130 mg of multiwalled carbon nanotubes, elution with 25 mL of dichloromethane for run-off and tap water and 30 mL for mineral water) allowed the quantitative extraction of analytes at levels lower than the maximum residues limits legislated by the European Union, with LODs between 1.16 and 93.6 ng/L. Absolute recovery values achieved were in the range of 67-107% (RSD values <10.1%).

Compound-specific carbon isotope analysis of short-chain fatty acids from Pine tissues: characterizing paleo-fire residues and plant exudates.

Different types of plant tissues and resin can account for the wax lipids found in sedimentary contexts and archaeological samples. Consequently, there is increasing research to characterize the fatty acid carbon isotope ratios of different plant anatomical parts and their plant exudates (resin). With the aim to explore isotopic differences between plant tissues, state of the fine organic matter, effect of thermal degradation, and to identify plant residues we measured the δ13C values of short-chain fatty acids (δ13C16:0 and δ13C18:0) in: i) dead and fresh (collected and immediately dried) pine needles and branches (Pinus canariensis) and pine resin from laboratory-controlled heating experiments and ii) sediment and charred pine tissue samples from a wild pine forest fire. Our results are compared to previously published experimental open-air fire experiments and pine-fuelled archaeological combustion features. We found that for both fatty acid types, there are differences in δ13C signatures among anatomical parts and initial moisture content. These data allow us to characterize the isotopic signature of pine tissue and the effect of degradation on isotopic biomarkers, as well as to estimate combustion temperatures in pine-fuelled anthropogenic fires. Supplementary Information: The online version contains supplementary material available at 10.1007/s12520-023-01815-3.

Monitoring of the presence of plasticizers and effect of temperature and storage time in bottled water using a green liquid-liquid microextraction method.

In this work, a natural deep eutectic solvent was used for the liquid-liquid microextraction of fourteen phthalates and one adipate from bottled waters. The methodology was validated in terms of matrix effect, linearity, recovery, and limits of quantification (LOQs). Optimum extraction conditions (10 mL of water at pH 8.0 with 100 µL of thymol: menthol 2:1 (n/n) as solvent) provided satisfactory determination coefficients (≥ 0.9977), recovery values (82-127%), and LOQs (0.018-0.523 µg/L). The effects of temperature and storage time on plasticizer presence were studied for 36 different brands stored at 4 °C, room temperature, and 45 °C, and analyzed at 0, 24, 48, 72 h, and 1 week. Only diethyl-, dibutyl-, bis-(2-ethylhexyl) phthalates, and bis-(2-ethylhexyl) adipate were detected. The results showed that there is no relationship between the storage conditions, the bottle material or water carbonation, and the occurrence of these plasticizers, suggesting that residues are introduced during production or by the water supply. The estimated daily intake was lower than the total daily intake set by the European Food Safety Authority.

Assessment of endocrine disruptor pollutants and their metabolites in environmental water samples using a sustainable natural deep eutectic solvent-based analytical methodology.

In this work, an evaluation of the occurrence of fifteen phthalates, four metabolites and one adipate in different groundwater, seawater and wastewater samples has been carried out due to their relevance on human health as they act as endocrine disruptors. For this purpose, a sustainable, fast and easy-handling vortex-assisted liquid-liquid microextraction method using a natural hydrophobic deep eutectic solvent based on menthol and carvacrol as extraction agent, combined with ultra-high performance liquid chromatography-mass spectrometry technique, has been developed and applied for the first time. An optimization was performed to evaluate four important factors affecting the extraction performance, and an analytical validation was carried out in terms of matrix effect, linearity, extraction efficiency, and sensitivity. Recovery values were obtained in the range 72-119% for all analytes (except for monoethyl phthalate: 61.1-72.3%) with relative standard deviation values lower than 17%. Limits of quantification were found between 0.91 and 8.09 µg L-1. As a result of the assessment of 31 different environmental water samples, monoethyl phthalate, diethyl phthalate, dibutyl phthalate and bis (2-ethylhexyl) phthalate were detected and quantified at different concentrations in the range 2.59-21.17 µg L-1 in 6 samples, and diallyl phthalate, butyl benzyl phthalate, dipentyl phthalate, dicyclohexyl phthalate, dihexyl phthalate and bis (2-ethylhexyl) adipate were detected in 20 more, showing the exposition of the population to these hazardous substances.

Assessment of pesticide residues contamination in cereals and pseudo-cereals marketed in the Canary Islands.

In this work, the development of an analytical method for the evaluation of a wide variety of pesticide residues in cereals and pseudo-cereals widely consumed has been carried out. A QuEChERS method was used as extraction and clean-up procedure prior to separation and quantification of the target analytes by ultra-high performance liquid chromatography coupled to mass spectrometry using a single quadrupole-time-of-flight analyser. The methodology was validated for oat, rye, spelt, barley and quinoa matrices, following the European Commission guidelines (SANTE/11312/2021), achieving good absolute recovery values in the range 60-124% with relative standard deviation values lower than 20% and providing limits of quantification of the method in the low mg/kg range, in accordance with the maximum residue limits established by European policies. Finally, considering the importance of cereals in general population diet, the analysis of 60 samples was carried out in order to assure their safe consumption.

Pesticide residue analysis in cereal-based baby foods using multi-walled carbon nanotubes dispersive solid-phase extraction.

In the present study, a new analytical method has been developed for the simultaneous quantification of 15 organophosphorus pesticides, including some of their metabolites, (disulfoton-sulfoxide, ethoprophos, cadusafos, dimethoate, terbufos, disulfoton, chlorpyrifos-methyl, malaoxon, fenitrothion, pirimiphos-methyl, malathion, chlorpyrifos, terbufos-sulfone, disulfoton-sulfone and fensulfothion) in three different types of commercial cereal-based baby foods. Dispersive solid-phase extraction (dSPE) with multi-walled carbon nanotubes (MWCNTs) was used together with gas chromatography with nitrogen phosphorus detection. Most favorable conditions involved a previous ultrasound-assisted extraction of the sample with acetonitrile containing formic acid. After evaporation of the extract and redissolution in water, a dSPE procedure was carried out with MWCNTs. The whole method was validated in terms of repeatability, linearity, precision and accuracy and matrix effect was also evaluated. Absolute recoveries were in the range 64-105 % with relative standard deviation values below 7.6 %. Limits of quantification achieved ranged from 0.31 to 5.50 µg/kg, which were lower than the European Union maximum residue limits for pesticide residues in cereal-based baby foods.

Analysis of alkylphenols, bisphenols and alkylphenol ethoxylates in microbial-fermented functional beverages and bottled water: Optimization of a dispersive liquid-liquid microextraction protocol based on natural hydrophobic deep eutectic solvents.

In this work, the analysis of alkylphenols, bisphenols and alkylphenol ethoxylates in bottled waters, kombuchas and water kefir was performed through a vortex-assisted dispersive liquid-liquid microextraction method based on a natural hydrophobic eutectic solvent. For this purpose, mixtures of monoterpenes and fatty acids were employed. Different factors affecting extraction were optimized and the method was validated in terms of matrix effect, linearity, limits of detection and recovery. Recovery values varied between 70.0 and 124.3% (except for 4-tert-butylphenol: 67.0% and 4-n-nonylphenol: 60.8% in water kefir) and limits of detection were in the range 0.10 ng/L - 2.99 µg/L. Finally, 8 bottled waters, 8 kombuchas and 4 water kefirs were analyzed and 4-tert-octylphenol monoethoxylate was detected in water (20.28 ± 0.99 - 62.08 ± 3.63 µg/L). This is the first application analyzing xenobiotic contaminants in kombucha and water kefir and the first time in which the three types of compounds are simultaneously extracted by dispersive liquid-liquid microextraction.

Dispersive liquid-liquid microextraction combined with nonaqueous capillary electrophoresis for the determination of fluoroquinolone antibiotics in waters.

Dispersive liquid-liquid microextraction (DLLME) was combined for the first time with NACE-UV for the selective determination of eight fluoroquinolone antibiotics (lomefloxacin, levofloxacin, marbofloxacin, ciprofloxacin, sarafloxacin, enrofloxacin, danofloxacin and difloxacin) in mineral and run-off waters. Field-enhanced sample injection was carried out in order to improve the sensitivity, whereas pipemidic acid was used as internal standard. The BGE that provided complete separation of the eight analytes and the internal standard was composed of 3 M acetic acid, 49 mM ammonium acetate in 55:45 v/v methanol:ACN. Optimum DLLME conditions (extraction of 5 mL of water at pH 7.6 with 685 µL of CHCl(3) and 1250 µL of ACN, extractant and disperser solvents, respectively) were achieved by means of experimental design methodology. Calibration curves of the whole method were obtained with correlation coefficients (R) higher than 0.994 in all cases. An accuracy and precision study was carried out at different levels of concentration, finding that there were no significant differences (Student's t-test) between real and spiked concentrations.

Micro-contextual identification of archaeological lipid biomarkers using resin-impregnated sediment slabs.

Characterizing organic matter preserved in archaeological sediment is crucial to behavioral and paleoenvironmental investigations. This task becomes particularly challenging when considering microstratigraphic complexity. Most of the current analytical methods rely on loose sediment samples lacking spatial and temporal resolution at a microstratigraphic scale, adding uncertainty to the results. Here, we explore the potential of targeted molecular and isotopic biomarker analysis on polyester resin-impregnated sediment slabs from archaeological micromorphology, a technique that provides microstratigraphic control. We performed gas chromatography-mass spectrometry (GC-MS) and gas chromatography-isotope ratio mass spectromety (GC-IRMS) analyses on a set of samples including drill dust from resin-impregnated experimental and archaeological samples, loose samples from the same locations and resin control samples to assess the degree of interference of polyester resin in the GC-MS and Carbon-IRMS signals of different lipid fractions (n-alkanes, aromatics, n-ketones, alcohols, fatty acids and other high polarity lipids). The results show that biomarkers within the n-alkane, aromatic, n-ketone, and alcohol fractions can be identified. Further work is needed to expand the range of identifiable lipid biomarkers. This study represents the first micro-contextual approach to archaeological lipid biomarkers and contributes to the advance of archaeological science by adding a new method to obtain behavioral or paleoenvironmental proxies.

Pesticide extraction from table grapes and plums using ionic liquid based dispersive liquid-liquid microextraction.

Room temperature ionic liquids (RTILs) have been used as extraction solvents in dispersive liquid-liquid microextraction (DLLME) for the determination of eight multi-class pesticides (i.e. thiophanate-methyl, carbofuran, carbaryl, tebuconazole, iprodione, oxyfluorfen, hexythiazox, and fenazaquin) in table grapes and plums. The developed method involves the combination of DLLME and high-performance liquid chromatography with diode array detection. Samples were first homogenized and extracted with acetonitrile. After evaporation and reconstitution of the extract in water containing sodium chloride, a quick DLLME procedure that used the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C(6)MIM][PF(6)]) and methanol was developed. The RTIL dissolved in a very small volume of acetonitrile was directed injected in the chromatographic system. The comparison between the calibration curves obtained from standards and from spiked sample extracts (matrix-matched calibration) showed the existence of a strong matrix effect for most of the analyzed pesticides. A recovery study was also developed with five consecutive extractions of the two types of fruits spiked at three concentration levels. Mean recovery values were in the range of 72-100% for table grapes and 66-105% for plum samples (except for thiophanate-methyl and carbofuran, which were 64-75% and 58-66%, respectively). Limits of detection (LODs) were in the range 0.651-5.44 microg/kg for table grapes and 0.902-6.33 microg/kg for plums, representing LODs below the maximum residue limits (MRLs) established by the European Union in these fruits. The potential of the method was demonstrated by analyzing 12 commercial fruit samples (six of each type).