Negative Matrix Effect Research Articles

Comprehensive assessment of clean-up strategies for optimizing an analytical multi-method to determine pesticides and mycotoxins in Brazilian medicinal herbs using QuEChERS-LC-TQ-MS/MS.

The use of medicinal herbs has increased significantly. However, the presence of pesticide residues and mycotoxins in medicinal herbs has generated constant discussion and concern among regulatory agencies. Developing and validating an analytical method for determining pesticides and mycotoxins in medicinal plants is challenging due to the naturally occurring substances in these plants. The purpose of this work was to develop and to optimize a sensitive, accurate, precise, effective QuEChERS method for simultaneous determination of over 160 pesticide and mycotoxin residues in complex medicinal plant matrices using LC-TQ-MS/MS. A comprehensive comparison of clean-up procedures and other parameters was conducted to achieve this goal. The validation procedure was performed according to SANTE 11312/2021. More polar analytes, such as acephate, methamidophos and omethoate, presented a higher negative matrix effect in both Melissa officinalis L. and Malva sylvestris L. However, other molecules, such as spirodiclofen, showed a 24% signal enhancement in M. officinalis and a 46% signal suppression in M. sylvestris, indicating that a representative matrix-matched calibration would lead to inaccurate quantification of the analyte. Accuracy and precision were satisfactory according to SANTE 11312/2021 for 157 pesticide residues and mycotoxins in M. officinalis and for 152 molecules in M. sylvestris. LOQs at 10 µg kg-1 were achieved for 117 pesticides in M. officinalis and 99 pesticides in M. sylvestris. Among the mycotoxins, all four aflatoxins (B1, B2, G1 and G2) presented LOQs of 5 µg kg-1, and ochratoxin A had an LOQ of 10 µg kg-1 in M. officinalis. The same LOQ values were shown for these mycotoxins in M. sylvestris, except for aflatoxin B2 and ochratoxin A, which had LOQs of 20 µg kg-1. Moreover, in Southern Brazil, there has been no previous study on mycotoxin and pesticide contamination in medicinal herbs. Therefore, the application of this method was assessed through the analysis of forty-two real samples. Imidacloprid was found in M. officinalis, and methyl pirimiphos was found in M. sylvestris. The proposed method not only serves as a helpful tool for routine monitoring but also offers a basis for further research on risk assessment and control in food safety.

Occurrence and Consequences of Matrix Effects in Simultaneous Multi-class LC-MS/MS Determination of Pesticides, Pharmaceuticals and Perfluoroalkylsubstances in Different Types of Groundwater

Matrix effects are a recent remarkable feature in quantitative LC-MS/MS analysis. In this work, the matrix effects of a multiclass mixture of 46 analytes - pesticides, pharmaceuticals and perfluoroalkylsubstances in different types of natural groundwater were studied. Groundwater samples were spiked with different standards from different chemical groups and determined by direct injection and liquid chromatography coupled to tandem mass spectrometry. Matrix effects were assessed by matrix factors calculated using the slope ratio technique. Groundwater samples were sampled in different boreholes in several places in Slovakia. The relationship with the various detected inorganic parameters was investigated and discussed. Most of the studied analytes showed negative matrix effects. Some analytes showed weak negative or positive matrix effects. The results show that average matrix factors obtained from different sampling sites are not a reliable tool and matrix effects need to be monitored depending on the sampling location. Only weak or no correlation of the matrix factors with the determined inorganic parameters was found. Geochemical composition of boreholes samples was determined and the differences in the macrochemical composition of the samples was evaluated. Model samples of ultrapure water enriched with NaCl, Na2CO3 and NaNO3 at various concentration levels were tested and the matrix effects were not observed. Other content of sample than cations Na+ were responsible for the matrix effects. It was found that the most affected compounds are sulfamethoxazole, sulfadiazine, metamitron, chloridazon and also caffeine. The results show that the detailed study is suitable as a tool for a deeper understanding of matrix effects in different types of groundwater. The proper ground water sample must be selected for reliable results of quantitative analysis.Graphical

A dilute-and-inject liquid-gas chromatography-mass spectrometry method for the analysis of sixteen polycyclic aromatic hydrocarbons in extra-virgin olive oil

BackgroundPolycyclic aromatic hydrocarbons (PAHs) represent a diverse group of organic compounds characterized by the fusion of two or more benzene rings arranged in various structural forms. Due to their harmful effects on human health, it is essential to implement monitoring systems and preventive measures to regulate human exposure. Given the affinity of PAHs for lipids, extensive research has been focused on their presence in vegetable oils. This study aimed to develop an on-line liquid-gas chromatography (LC-GC) method (using tandem mass spectrometry) with minimized solvent consumption for the determination of 16 PAHs in extra-virgin olive oil (EVOO). ResultsA side-by-side comparison of the selected-ion-monitoring and the pseudo multiple-reaction-monitoring (p-MRM) acquisition modes was performed, in terms of specificity and detectability. The results obtained using the p-MRM mode were superior, and for this reason it was selected. The method was linear over the concentration range 1–200 μg kg−1 (except in five cases, over 2–200 and 5–200 μg kg−1 ranges). Accuracy (at the 2 μg kg−1 and 20 μg kg−1 concentration levels) was in the 86.9–109.3 % range, with an RSD <10 %. Intra-day and inter-day precision (at 2 μg kg−1 and 20 μg kg−1 concentration levels) were in the 1.2–9.7 % and 3.2–10.8 % ranges, respectively. For all the PAHs, a negative matrix effect was observed. Three out of sixteen PAHs were detected in three EVOOs (among ten samples), albeit at the low ppb level. Limits of quantification were satisfactory in relation to EU legislation on the presence of PAHs in vegetable oils. SignificanceA dilute-and-inject LC-GC-tandem mass spectrometry method is herein proposed fulfilling EU legislation requirements; sample preparation was very simple, inasmuch that it involved only a dilution step, thus avoiding extraction, clean-up, and thus a high consumption of organic solvents. In fact, considering both oil dilution and the LC mobile phase, less than 8 mL of solvents were used.

Interaction between Six Waxy Components in Summer Black Grapes (Vitis vinifera) and Mancozeb and Its Effect on the Residue of Mancozeb.

Mancozeb, an antifungal typically used for the growth of fruits, has the characteristic of non-internal absorption, and has a risk of binding to the waxy components of fruits. This work investigated the interaction of pesticide molecules with the waxy layer on the grape surface and their effects on pesticide residues in grapes. The study observed significant changes in the compositions of the waxy layer on the grape surface after soaking in a mancozeb standard solution. The six substances-oleanolic acid, ursolic acid, lupeol, octacosanol, hexacosanal, and γ-sitosterol-with discernible content differences were chosen for molecular docking. Docking results were further visualized by an independent gradient model based on Hirshfeld partition (IGMH). Hydrogen bonds and van der Waals forces were found between mancozeb and the six waxy components. Moreover, the negative matrix effects caused by the presence or absence of wax for the determination of mancozeb were different through the QuEChERS-HPLC-MS method. Compared with the residue of mancozeb in grapes (5.97 mg/kg), the deposition of mancozeb in grapes after dewaxing was significantly lower (1.12 mg/kg), which further supports that mancozeb may interact with the wax layer compositions. This work not only provides insights into the study of the interaction between pesticides and small molecules but also provides theoretical guidelines for the investigation of the removal of pesticide residues on the surface of fruits.

Frontiers of protected areas versus forest exploitation: Assessing habitat network functionality in 16 case study regions globally

Exploitation of natural forests forms expanding frontiers. Simultaneously, protected area frontiers aim at maintaining functional habitat networks. To assess net effects of these frontiers, we examined 16 case study areas on five continents. We (1) mapped protected area instruments, (2) assessed their effectiveness, (3) mapped policy implementation tools, and (4) effects on protected areas originating from their surroundings. Results are given as follows: (1) conservation instruments covered 3–77%, (2) effectiveness of habitat networks depended on representativeness, habitat quality, functional connectivity, resource extraction in protected areas, time for landscape restoration, “paper parks”, “fortress conservation”, and data access, (3) regulatory policy instruments dominated over economic and informational, (4) negative matrix effects dominated over positive ones (protective forests, buffer zones, inaccessibility), which were restricted to former USSR and Costa Rica. Despite evidence-based knowledge about conservation targets, the importance of spatial segregation of conservation and use, and traditional knowledge, the trajectories for biodiversity conservation were generally negative.

Prompt-gamma activation analysis and neutron imaging of layered metal structures

We present here Monte Carlo computer simulations to broaden the scope of the prompt-gamma activation analysis (PGAA) from the elemental composition measurement of ideal, point-like, homogeneous samples towards non-homogeneous or heterogeneous but still regularly-shaped samples. The successful correction for the negative matrix effect related to the neutron self-shielding and gamma self-absorption is a key step in the quantitative analysis of layered metal structures. This geometry is relevant to practical cases where corrosion layer, patina, paint, coating, gilding, or segregation are present on the surface of a core metal. Linear neutron attenuation coefficients are measured in a polychromatic neutron beam by radiography, while the gamma attenuation calculations by MCNP6 simulations were validated by gamma transmission measurements. Finally, the method was successfully applied to correct for the PGAA matrix effect in double- and triple-layer metal stacks and a real structured numismatic sample.

A Simple and Efficient Extraction Method for the Preconcentration of Copper in Tap Water and Linden Tea Samples Prior to FAAS Measurement

AbstractIn this study, a simple, low‐cost and eco‐friendly analytical method namely syringe assisted pipette tip dispersive solid phase extraction (SA‐PT‐DSPE) combined with slotted quartz tube‐flame atomic absorption spectrometry (SQT‐FAAS) system was presented for the determination of copper at trace levels in linden tea and tap water samples. Under the optimal experimental conditions, limit of detection (LOD) and quantification (LOQ) values obtained for the SA‐PT‐DSPE‐SQT‐FAAS system were calculated as 3.7 and 12.5 μg/L, respectively. The SA‐PT‐DSPE‐SQT‐FAAS system provided a 44.0‐folds improvement in detection power of the conventional FAAS. The recovery results for tap water samples were calculated close to 100 % via external calibration strategy. Negative matrix effects on the analyte were observed for linden tea samples. Therefore, recovery studies were performed by matrix matching calibration strategy and percentage recoveries were found to be between 88.0–102.0 % with low standard deviation values.

Combination of an Efficient Photochemical Vapor Generation System and Flame Atomic Absorption Spectrophotometry for Trace Nickel Determination in Wastewater Samples

A photochemical vapor generation – atomic absorption spectrometry combination was applied for the determination of nickel. Optimizations of low molecular weight organic acid type, concentration of low molecular weight organic acid, ultraviolet irradiation period, mixing type and period, flow rate of carrier gas, and temperature of atomizer were conducted in order to maximize analytical signals. Under the optimum conditions, analytical performance of the photochemical vapor generation – atomic absorption spectrometry system was evaluated; the limits of detection and quantification were determined to be 3.5 and 11.6 µg/L, respectively. Spiking experiments were carried out in wastewater samples to investigate the applicability and accuracy of the developed method. Matrix matching calibration was used to calculate the recovery since negative matrix effects (approximately 45%) were observed on the analyte with external calibration. The recovery results for 40, 60 and 80 µg/L of spiked concentration were determined to be 106.2%, 101.4% and 99.0%, respectively, indicating the high accuracy of the developed method for the selected matrix.

Matrix effect evaluation and validation of the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) radical cation scavenging assay, as well as its application using a tejate, an ancient beverage in Mexico

Nowadays, consumers, food industries, and researchers have a great interest in evaluating the total antioxidant value of foodstuffs and plasma samples. The 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging assay is one of the most common antioxidant evaluations. However, this assay shows a great variability in its methodology, e.g., the use of a phosphate buffered saline (PBS) matrix. Moreover, all prior assays did not describe a complete validation procedure. This study demonstrated that the matrix of calibration standards had a significant effect on the accuracy of antioxidant measurements, under the ABTS radical cation scavenging assay. A PBS matrix should only be used in this assay during plasma analysis due to a negative matrix effect on calibration curves. Meanwhile, a PBS-free matrix should be used during analyses of water-based beverages. Our analytical validation showed that the current assay had an inverse lineal relationship, acceptable range, sensitivity, precision, accuracy, short and long-term stability, selectivity, identity, and short time of analysis. Additionally, this study showed that a traditional Southern Mexico beverage (tejate) had antioxidant properties (inhibition of the ABTS radical cation and ability to reduce the ferric ion) due to the presence of polyphenol compounds. The biological relevance was supported by a high plasma antioxidant activity in rats after a 7-day period of tejate consumption.

Analytical validation of a conventional cardiac troponin I assay for dogs and cats.

Cardiac troponins are gold-standard biomarkers of myocardial injury. There is a need for validation of assays with higher availability and lower costs in veterinary medicine. The primary aim of the present study was to perform an analytical validation of the IMMULITE 2000 TnI assay for use in dogs and cats. A secondary aim was to evaluate its agreement with the previously validated and sensitive Siemens ADVIA Centaur TnI-Ultra assay. Intra- and inter-assay variation, detection limits, the linearity under dilution, and a sample addition study (modified spike-and-recovery analysis) were investigated to assess analytical performance in 15 canine and 15 feline serum samples. Agreement between the assays was evaluated by correlation and Bland-Altman analyses including an additional 99 canine serum samples. Intra-assay variation of cTnI in canine and feline serum was 3.71% and 4.68%, while inter-assay variation was 5.88% and 6.54%, respectively. The assay performed with acceptable linearity within a clinically relevant range of serum cTnI concentrations. The sample addition study revealed insufficient recovery in the range of 71.9%-81.4% for dogs and 62.6%-75.7% for cats. This was considered to be due to a negative matrix effect. A significant correlation between the assays was found, and the Bland-Altman analysis showed acceptable agreement for a wide range of concentrations, but revealed a proportional error, with the IMMULITE TnI assay consistently measuring a higher concentration than the Centaur TnI-Ultra assay. This was relevant only at high serum cTnI concentrations. The IMMULITE TnI assay is considered acceptable for clinical use in dogs and cats.

Analysis of polyhalogenated carbazoles in sediment using liquid chromatography–tandem mass spectrometry

The purpose of this study was to develop a novel and sensitive method for the analysis of carbazole and polyhalogenated carbazoles (PHCs) in sediment using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Briefly, 5.0 g of freeze-dried sediment samples were extracted with dichloromethane using pressurized liquid extraction (PLE). The extract was purified with Florisil solid phase extraction cartridge, filtered through 0.22 µm polytetrafluoroethylene filter using a glass syringe, followed by LC-MS/MS analysis. Besides parameters for LC-MS/MS analysis, sample preparation procedures (including solvents for PLE, sorbents for cleanup, and filters for sample filtration) were optimized. The limits of detection and limits of quantification of target compounds were in the ranges of 3.0 × 10−3 to 0.22 ng g−1 dry weight (d.w.) and 1.0 × 10−2 to 0.75 ng g−1 d.w., respectively. The recoveries of target compounds in the spiked sediments at 2.0 ng g−1 d.w. and 10 ng g−1 d.w. were 64.8–91.8% and 70.9–124.7%, respectively, with relative standard deviations being less than 13.2%. Except that 36-BCZ had positive matrix effects of 63.3%, the sediment matrices generally displayed low or medium negative matrix effects on the other target compounds during LC-MS/MS analysis. The developed method was applied in the analysis of carbazoles and PHCs in sediment samples from Jiulong River, Fujian, China and all the target compounds were detected in the samples.

Validation of a method for extraction of polycyclic aromatic hydrocarbons from sewage sludge and analysis by GC-MS

ABSTRACTIn the present study, the solid–liquid extraction with low temperature purification was validated for the determination of 16 polycyclic aromatic hydrocarbons from sewage sludge by gas chromatography-mass spectrometry. Recoveries ranged 70–114% for naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene and chrysene, while the compounds benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene and benzo[g,h,i]perylene showed recoveries of between 40 and 70%. The relative standard deviation was less than 13% for all of the compounds. Negative matrix effect was observed on the 10 compounds with less retention time in the chromatographic analysis and positive matrix effect noticed on the others. The limits of quantification were from 2 to 20 μg kg−1, about 30 times less than the maximum residue limit allowed in sludge by the European Union. The validated method produced quantification of 11 PAHs in one sludge sample at concentrations ranging 20–2000 μg kg−1.

Evaluation of the TLC quantification method and occurrence of deoxynivalenol in wheat flour of southern Brazil

ABSTRACTThe study evaluated a QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) extraction method for use with a TLC quantification procedure for deoxynivalenol (DON). It also surveyed DON occurrence in wheat flour from the southern region of Brazil. Forty-eight wheat flour samples were analysed, divided into 2 different harvest lots, each consisting of 24 different brands. The detection and quantification limits of the method were 30 and 100 ng of DON on the TLC plate. The various concentrations of DON presented high linearity (R2 = 0.99). A negative matrix effect (−28%) of the wheat flour was verified, with suppression of the chromatographic signal of DON, and 80.2–105.4% recovery. The TLC method was reliable for DON evaluation, with a coefficient of variation of less than 10%. High-performance liquid chromatography of lot 2 samples confirmed the presence of DON in all samples identified DON-positive by the TLC technique. Of the 48 wheat flour samples in lots 1 and 2 analysed by TLC, 33.3 and 45.8% of the samples respectively were above the Brazilian legislation limit. Correlations were observed between the water activity and DON content, and between the fungal count and moisture content of the wheat flours.

Evaluation and prevention of the negative matrix effect of terpenoids on pesticides in apples quantification by gas chromatography–tandem mass spectrometry

The sample matrix can enhance the gas chromatography signal of pesticide residues relative to that obtained with the same concentration of pesticide in solvent. This paper is related to negative matrix effects observed in coupled gas chromatography-mass spectrometry ion trap (GC/MS2) quantification of pesticides in concentrated extracts of apple peel prepared by the Quick Easy Cheap Effective Rugged and Safe (QuEChERS) method. It is focused on the pesticides most frequently used on the apple varieties studied, throughout the crop cycle, right up to harvest, to combat pests and diseases and to improve fruit storage properties. Extracts from the fleshy receptacle (flesh), the epiderm (peel) and fruit of three apple varieties were studied by high-performance thin-layer chromatography hyphenated with UV–vis light detection (HPTLC/UV visible). The peel extracts had high concentrations of triterpenic acids (oleanolic and ursolic acids), reaching 25mgkg−1, whereas these compounds were not detected in the flesh extracts (<0.05mgkg−1). A significant relationship has been found between the levels of these molecules and negative matrix effects in GC/MS2. The differences in the behavior of pesticides with respect to matrix effects can be accounted for by the physicochemical characteristics of the molecules (lone pairs, labile hydrogen, conjugation). The HPTLC/UV visible method developed here for the characterization of QuEChERS extracts acts as a complementary clean-up method, aimed to decrease the negative matrix effects of such extracts.

Towards coupling dispersive liquid-liquid microextraction with hollow fibre liquid phase microextraction for extraction of organic pollutants of agricultural origin

Liquid-based miniaturized techniques have received a lot of attention recently resulting in the development of the liquid phase microextraction (LPME) and dispersive liquid-liquid microextraction (DLLME) techniques each offering unique benefits over the other technique. Herein we report a combination of the two techniques for the extraction of hexestrol and atrazine from aqueous systems. The method sets off with the DLLME thereafter a hollow fibre filled with the organic solvent is introduced for the extraction of the pre-extracted analytes in the dispersed organic solvent. The method was modified further by introducing a second extracting solvent in place of the disperser solvent. Under the optimum conditions, namely, toluene in the acceptor phase, 1:1 chloroform:toluene (v/v) as a dispersed solvent, 15% NaCl, with the 15 min extraction time, the method achieved satisfactory enrichment factors (87- and 62-fold); sufficiently low detection limits of 0.018 μg/mL and 0.016 μg/mL using the flame ionization detector, while 0.072 and 0.063 ng/mL were obtained using single ion monitoring mass spectrometry detector, for atrazine and hexestrol, respectively; with sufficient linearity (R2 ≥ 0.9959). Although the compounds were not detected in the river water sample, satisfactory recoveries (111–115%) were achieved indicating the method did not suffer any negative matrix effect.

Matrix-Matching as an Improvement Strategy for the Detection of Pesticide Residues.

More than 90% of the pesticides residues in apples are located in the peel. We developed a gas chromatography/ion trap tandem mass spectrometry method for investigating all detectable residues in the peel of 3 apple varieties. Sample preparation is based on the use of the Quick Easy Cheap Effective Rugged and Safe method on the whole fruit, the flesh, and the peel. Pesticide residues were quantified with solvent-matched and matrix-matched standards, by spiking apple sample extracts. Matrix effects dependent on the type of extract (fruit, flesh, or peel) and the apple variety were detected. The best data processing methods involved normalizing matrix effect rates by matrix-matched internal/external calibration. Boscalid, captan, chlorpyrifos, fludioxonil, and pyraclostrobin were the most frequently detected pesticides. However, their concentrations in the whole fruit were below European maximum residue levels. Despite negative matrix effects, the residues in peel were detected at concentrations up to 10 times higher than those in whole fruits. Consequently, other pesticide residues present at concentrations below the limit of quantification in the whole fruit were detected in the peel.

Non-spectral interferences due to the presence of sulfuric acid in inductively coupled plasma mass spectrometry

Results of a systematic study concerning non-spectral interferences from sulfuric acid containing matrices on a large number of elements in inductively coupled plasma–mass spectrometry (ICP-MS) are presented in this work. The signals obtained with sulfuric acid solutions of different concentrations (up to 5% w w−1) have been compared with the corresponding signals for a 1% w w−1− nitric acid solution at different experimental conditions (i.e., sample uptake rates, nebulizer gas flows and r.f. powers). The signals observed for 128Te+, 78Se+ and 75As+ were significantly higher when using sulfuric acid matrices (up to 2.2-fold for 128Te+ and 78Se+ and 1.8-fold for 75As+ in the presence of 5 w w-1 sulfuric acid) for the whole range of experimental conditions tested. This is in agreement with previously reported observations. The signal for 31P+ is also higher (1.1-fold) in the presence of sulfuric acid. The signal enhancements for 128Te+, 78Se+, 75As+ and 31P+ are explained in relation to an increase in the analyte ion population as a result of charge transfer reactions involving S+ species in the plasma. Theoretical data suggest that Os, Sb, Pt, Ir, Zn and Hg could also be involved in sulfur-based charge transfer reactions, but no experimental evidence has been found. The presence of sulfuric acid gives rise to lower ion signals (about 10–20% lower) for the other nuclides tested, thus indicating the negative matrix effect caused by changes in the amount of analyte loading of the plasma.The elemental composition of a certified low-density polyethylene sample (ERM-EC681K) was determined by ICP-MS after two different sample digestion procedures, one of them including sulfuric acid. Element concentrations were in agreement with the certified values, irrespective of the acids used for the digestion. These results demonstrate that the use of matrix-matched standards allows the accurate determination of the tested elements in a sulfuric acid matrix.

Analysis of tomato matrix effect in pesticide residue quantification through QuEChERS and single quadrupole GC/MS

The detection of pesticide in tomato (Solanum lycopersicum L.) matrix using Gas Chromatography hyphenated to Mass Spectrometry detector (GC/MS) can affect the sensitivity of the analysis by enhancement or suppression of their chromatography response, the percentages of recoveries and leading to errors in the quantification of the pesticides. In this study, the matrix effect was investigated using nine pesticides, and Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS)-GC/MS analytical technique was validated for pesticides multiresidue analysis. The matrix effect was determined using not statistical and statistical procedures including ANOVA, with similar results. Strong negative matrix effect was found for the pesticides trifluralin, 4,4'-DDT, and permethrin, resulting in the increment of the chromatogram background and a decrease in their detection responses. Contrary, an enhancement induced by the matrix presence was obtained for carbaryl and azinphos methyl, showing a positive medium matrix effect. While, dimethoate, simazine, 4,4'-DDE, and iprodione did not exhibit matrix effect. The detection limits (LOD) obtained, varied from 0.003 to 0.1 mg kg-1. Reproducibility was less than 20% for each pesticide. Recoveries were found to be between 71% and 121%, except for dimethoate, carbaryl, and azinphos methyl which reached values lower than 70%. Recoveries relative standard deviations were less than 22%. QuEChERS-GC/MS technique was used for evaluation of fresh commercial tomatoes samples, detecting carbaryl in all of them, but in concentration levels lower than the maximum residue limits according to regulations of Codex.

Matrix effect and retention efficiency of hydrophilic-lipophilic balance cartridges in multi-residual determination of veterinary drugs in river water

Matrix effect is an important interfering factor in LC-MS quantitative analysis. In this paper, matrix effects and retention efficiencies of 33 veterinary drugs spiked in river water were studied on hydrophilic-lipophilic balance (HLB) cartridges of 3 brands (Waters, Supelco, and CNW), using LC-MS/MS for detection and reverse osmosis (RO) water as the control under 500-fold concentration. In RO water, only the exogenous matrix effects were observed on three brands of HLB cartridges. Most quinolones and tetracyclines showed positive matrix effects. Estrogens showed negative matrix effects on two brands of HLB cartridges. Sulfonamides were not obviously affected by matrix effects. Chloramphenicols showed negative matrix effects on one brand of HLB cartridge. In river water, matrix effects were different from those of the RO water due to the combined exogenous and endogenous interfering substances. Sulfonamides showed slight matrix effects as those in RO water. Most quinolones and tetracyclines showed positive matrix effects. Chloramphenicols and estrogens showed negative matrix effects. Compared to the external standard method, matrix matched calibration method effectively overcame the matrix effects with better quantitative results. The recoveries of 33 target veterinary drugs spiked in river water at 50 ng/L and 200 ng/L levels were in the ranges of 40.3%-146.0% (Waters), 37.8%-104.2% (Supelco), and 52.9%-150.1% (CNW) with RSDs (n = 4) of 0.2%-14.6%. The results indicated that there was no significant difference in the retention efficiency between the 3 HLB cartridges with the matrix matched calibration method. This study provided supporting data for the HLB cartridge selection in multi-residual determination of the veterinary drugs in river water samples.

Evaluation of matrix effect on the GC response of eleven pesticides by PCA

Abstract The components of seven matrices in the analysis of 11 pesticides by GC-ECD were analysed. The matrix effect was calculated based on the changing of chromatographic response of the analyte in the presence of co-extractives of the matrices in the organic phase obtained by solid–liquid and liquid–liquid extraction with partition at low temperature (ESL-PBT and ELL-PBT), in relation to the response of it in the pure solvent. It was used the Principal Component Analysis (PCA) in evaluating the results obtained for the percentages of the matrix effect. The tomato, grape and pineapple matrices caused greater matrix effect and were grouped. The other matrices such as apple, water and potato caused small matrix effect. For most pesticides the soil matrix caused negative matrix effect. The influence of pH of the samples on the matrix effect was also evaluated showing not to have a direct effect on the phenomenon.