Screening and quantification of pesticide residues in fruits and vegetables making use of gas chromatography–quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization

An atmospheric pressure chemical ionization source has been used to enhance the potential of gas chromatography coupled with quadrupole time-of-flight (QTOF) mass spectrometry (MS) for screening and quantification purposes in pesticide residue analysis. A screening method developed in our laboratory for around 130 pesticides has been applied to fruit and vegetable samples, including strawberries, oranges, apples, carrots, lettuces, courgettes, red peppers, and tomatoes. Samples were analyzed together with quality control samples (at 0.05 mg/kg) for each matrix and for matrix-matched calibration standards. The screening strategy consisted in first rapid searching and detection, and then a refined identification step using the QTOF capabilities (MS^E and accurate mass). Identification was based on the presence of one characteristic m/z ion (Q) obtained with the low collision energy function and at least one fragment ion (q) obtained with the high collision energy function, both with mass errors of less than 5 ppm, and an ion intensity ratio (q/Q) within the tolerances permitted. Following this strategy, 15 of 130 pesticides were identified in the samples. Afterwards, the quantitation capabilities were tested by performing a quantitative validation for those pesticides detected in the samples. To this aim, five matrices were selected (orange, apple, tomato, lettuce, and carrot) and spiked at two concentrations (0.01 and 0.1 mg/kg), and quantification was done using matrix-matched calibration standards (relative responses versus triphenyl phosphate used as an internal standard). Acceptable average recoveries and relative standard deviations were obtained for many but not all pesticide–matrix combinations. These figures allowed us to perform a retrospective quantification of positives found in the screening without the need for additional analysis. Taking advantage of the accurate-mass full-spectrum data provided by QTOF MS, we searched for a higher number of compounds (up to 416 pesticides) in a second stage by performing extra data processing without any new sample injection. Several more pesticides were detected, confirmed, and/or tentatively identified when the reference standard was unavailable, illustrating in this way the potential of gas chromatography–QTOF MS to detect pesticides in addition to the ones targeted in quantitative analysis of pesticides in food matrices. Figure

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Controlled pesticide release from biodegradable polymers

Polymers have been widely used in agriculture for applications including controlled release of pesticides and other active ingredients. The ability to predict their delivery helps avoid environmental hazards. Macromolecular matrices used as carriers in controlled release of agricultural active agents, especially pesticides, are reviewed. The review focuses on the advantages and mechanisms of controlled release. It includes biodegradable polymers in agriculture, their manufacturing methods, and their degradation mechanisms and kinetics. The article also presents a critical account of recent release studies and considers upcoming challenges.      

Rapid detection of pesticides not amenable to multi-residue methods by flow injection–tandem mass spectrometry

Flow injection combined with tandem mass spectrometry (MS/MS) was investigated for the rapid detection of highly polar pesticides that are not amenable to multi-residue methods because they do not partition into organic solvents and require dedicated chromatographic conditions. The pesticides included in this study were amitrole, chlormequat, cyromazine, daminozide, diquat, ethephon, fosetyl-Al, glufosinate, glyphosate and its metabolite aminomethylphosphonic acid, maleic hydrazide, mepiquat and paraquat. The composition of the flow-injection solvent was optimized to achieve maximum MS/MS sensitivity. Instrumental limits of detection varied between <0.05 and 1 pg. Fruit, vegetable, cereal, milk and kidney samples were extracted with water (1 % formic acid in case of paraquat/diquat) and ten times diluted in either methanol/0.1 % formic acid, methanol/0.1 % ammonia or acetonitrile/0.1 % ammonia, depending on the pesticide. The ion suppression observed depended strongly on both the matrix and the pesticide. This could be largely compensated for by matrix-matched calibration, but more accurate quantification was obtained by using isotopically labelled standards (commercially available for most of the pesticides studied). The method detection limits ranged from 0.02 mg/kg for chlormequat and mepiquat to 2 mg/kg for maleic hydrazide and were 0.05–0.2 mg/kg for most other pesticide/matrix combinations. This was sufficiently low to test compliance with EU maximum residue limits for many relevant pesticide/commodity combinations. The method substantially reduces the liquid chromatography–MS/MS capacity demand which for many laboratories is prohibitive for inclusion of these pesticides in their monitoring and surveillance programmes. Figure

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Vortex-assisted ionic liquid based liquid-liquid microextraction of selected pesticides from a manufacturing wastewater sample

The ionic liquid based vortex-assisted liquid-liquid microextraction (IL-VALLME) procedure was developed and validated for determination of four pesticides in a manufacturing wastewater sample: acetamiprid, imidacloprid, linuron and tebufenozide. The following ILs were tested as extractants: 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-methyl-3-octylimidazolium hexafluorophosphate. The extraction efficiency and the enrichment factor dependencies on the type and amount of ionic liquids, extraction and centrifugation time, volume, pH and the ionic strength of the sample, were investigated. The concentration of pesticides in the aqueous and IL phases was determined by HPLC-DAD. The optimal conditions for extraction of the pesticides were determined: the aqueous sample volume of 10 mL with the addition of 0.58 g NaCl, 40 µL of the 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as extractant, 2 min extraction under vigorous mixing applying the vortex agitator, and separation of the phases by centrifugation for 2 min at 1000 rpm. The calibration curves of the pesticides showed good linear relationship (r² ≥ 0.9996) in the concentration range from 0.005 to 1.00 mg L^?1. Determined LOD values are 1.8, 2.3, 4.8 and 8.6 µg L^?1 for Tebf, Linr, Acet and Imid, respectively. The optimized IL-VALLME was applied for determination of the pesticides in the pesticide manufacturing wastewater.      

Multiresidue determination of pyrethroid pesticide residues in pepper through a modified QuEChERS method and gas chromatography with electron capture detection

This study developed and used a modified quick, easy, cheap, efficient, rugged and safe (QuEChERS) method coupled with gas chromatography with electron capture detection to determine eight pyrethroid pesticide residues in green, red and dehydrated red peppers. Pyrethroids were extracted with acetonitrile, partitioned with sodium chloride and purified with primary secondary amino and graphitized carbon black in hexane. The QuEChERS extraction conditions were optimized, and the matrix effects that might influence recoveries were evaluated and minimized using matrix‐matched calibration curves. Under the optimized conditions, the calibration curves for pyrethroid pesticides showed good linearities in the concentration range of 0.05–20 µg/mL with determination coefficients (R²) >0.997. The limits of quantification of eight pyrethroids were 0.004–0.04 mg/kg for green and red pepper and 0.04–0.5 mg/kg for dehydrated red pepper. These values are below the suggested regulatory maximum residue limits. The mean recoveries ranged between 79.0 and 104%, and the relative standard deviations were <11%. The developed method was successfully applied to commercial samples. Some samples were found to contain pyrethroid pesticides with levels below the legal limits. Copyright © 2015 John Wiley & Sons, Ltd.     

DNA-based biosensors with external Nafion and chitosan membranes for the evaluation of the antioxidant activity of beer,coffee, and tea

Novel electrochemical DNA-based biosensors with outer-sphere Nafion and chitosan protective membranes were prepared for the evaluation of antioxidant properties of beverages (beer, coffee, and black tea) against prooxidant hydroxyl radicals. A carbon working electrode of a screen-printed three-electrode assembly was modified using a layer-by-layer deposition technique with low molecular weight double-stranded DNA and a Nafion or chitosan film. The membrane-covered DNA biosensors were initially tested with respect to their voltammetric and impedimetric response after the incubation of the beverage and the medium exchange for the solution of the redox indicator [Fe(CN)₆]^3?/4?. While the Nafion-protected biosensor proved to be suitable for beer and black tea extracts, the chitosan-protected biosensor was successfully used in a coffee extract. Afterwards, the applicability was successfully verified for these biosensors for the detection of a deep degradation of the surface-attached DNA at the incubation in the cleavage agent (hydroxyl radicals generated via Fenton reaction) and for the evaluation of antioxidant properties of coffee and black tea extracts against prooxidant hydroxyl radicals. The investigation of the novel biosensors with a protective membrane represents a significant contribution to the field of electrochemical DNA biosensors utilization.      

Enantioselective inhibition of immobilized acetylcholinesterase in biosensor determination of pesticides

Chiral effects for the inhibition of acetylcholinesterase by organophosphorus pesticides were investigated for insecticide malathion and malaoxon, which is a metabolic product of malathion in living organisms. Studies were carried out using a bienzymatic biosensor with immobilized acetylcholinesterase, choline oxidase, and with Prussian Blue used as a mediator. In both cases the R enantiomers accelerate acetylocholinesterase inhibition. The chiral effect in inhibition was much more pronounced in fast flow measurements than in batch measurements.      

Synthesis and characterization of nanosized NiO2 and NiO using Triton® X-100

Nanosized NiO₂ particles with an average diameter of 15 nm are prepared by treating of Ni(NO₃)₂ · 6H₂O with an aqueous solution of KClO in the presence of Triton® X-100. This black fine powder of nickel peroxide was characterized by XRD diffraction, energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The as-prepared NiO₂ can be easily transformed to nanosized NiO merely by washing it with acetone. The obtained NiO has an average diameter of 40 nm and was characterized by the same means used for NiO₂. The nanoparticles of NiO₂ and NiO were obtained in high yields and purities.      

Aqueous photocatalytic oxidation of prednisolone

The research into the aqueous photocatalytic oxidation of the anti-inflammatory drug prednisolone was undertaken with P25 titanium dioxide (Evonik) and visible light-sensitive sol-gel synthesized titania-based photocatalysts containing carbon, sulphur, and iron. Possible prednisolone photocatalytic oxidation reaction pathways were proposed based on a number of oxidation by-products determined in the present study. The prednisolone adsorption properties, effects of initial prednisolone concentration, pH, usual wastewater matrix admixtures, like carbamide and sucrose, were studied. The nontoxicity of doped catalysts towards Tetrahymena thermophila, a ciliate protozoa present in the activated sludge, indicated their lower oxidative ability compared to P25, but also implied their potential application in pre-treatment of toxic hazardous materials under VIS or solar radiation before the biological degradation stage.      

Copper(I) π-complexes with allyl derivatives of heterocyclic compounds: structural survey of their crystal engineering

In this review an exhaustive crystallochemical analysis of copper(I) π-complexes with allyl derivatives of heterocyclic compounds has been performed. Structural genesis of inorganic constituents starting from the simplest units to the most complicated aggregates was considered taking into account the specific role of Cu-(C=C) interaction, the construction of the organic ligands, the basicity and nucleophilic activity of their heteroatoms, as well as olefin Cu(I) π-complex preparation route.      

Voltammetric behavior and quantitative determination of ambazone concentrations in urine and in a pharmaceutical formulation

The use of square wave adsorptive stripping voltammetry (SWAdSV) in conjunction with a cyclic renewable silver amalgam film electrode (Hg(Ag)FE) for the analytical determination of ambazone in urine samples and pharmaceutical formulations is described. A single reduction peak in Britton-Robinson buffer at pH 4.0 was detected at about ?1.4 V versus Ag/AgCl. Mechanistic studies have shown that the compound can act as an electrocatalyst. The method was validated. The analytical curve was linear in the concentration range from 1.0×10^?9 to 1.0×10^?7 mol L^?1. The detection and quantification limits were found to be 3.0×10^?10 mol L^?1 and 1.0×10^?9 mol L^?1, respectively. The proposed method was successfully applied to ambazone determination in real samples.      

Multiresidue determination of 29 pesticide residues in pepper through a modified QuEChERS method and gas chromatography–mass spectrometry

This study describes the development and use of a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with gas chromatography with mass spectrometry to determine 29 pesticide residues in green, red and dehydrated red peppers. Pesticides were extracted with acetonitrile (1% acetic acid), partitioned with sodium chloride and purified with primary secondary amino and octadecyl silane in acetone. The QuEChERS extraction conditions were optimized, and the matrix effects that might influence recoveries were evaluated and minimized using matrix‐matched calibration curves. Under the optimized conditions, the calibration curves for 29 pesticides showed good linearity in the concentration range of 0.1–10 μg/mL with determination coefficient R² > 0.998. The limits of quantification of the 29 pesticides were 0.006–0.06 mg/kg for green pepper, 0.005–0.039 mg/kg for red pepper and 0.014–0.25 mg/kg for dehydrated red pepper. These values are below the suggested regulatory maximum residue limits. The mean recoveries ranged between 70.1 and 110%, and the relative standard deviations were <13%. The developed method was successfully applied to commercial samples. Some samples were found to contain the 29 pesticides with levels below the legal limits. Copyright © 2016 John Wiley & Sons, Ltd.     

Quantification of sunscreen 2-phenylbenzimidazole-5-sulfonic acid in cosmetic products and water samples by HPTLC/densitometry with fluorescent detection

The water-soluble sunscreen 2-phenylbenzimidazole-5-sulfonic acid (PBS) was quantified in a sun-care product and water samples by thin layer chromatography followed by densitometric scanning in fluorescence mode (cut-off filter 370 nm, wavelength of excitation — 300 nm). Normal phase TLC was performed on silica gel 60 as stationary phase. Mobile phase used was ethyl acetate-ethanol-water 70:35:30 (v/v/v). The limit of detection (LOD) was 0.0004 μg spot-1, and the limit of quantification (LOQ) was — 0.001 μg spot^?1 without any sample pre-concentration.      

Carbon nanotube-ionic liquid nanocomposite modified carbon-ceramic electrode for determination of dopamine in real samples

Room temperature 1-butyl-3-methylimidazolium tetraflouroborate ([BMIM][BF₄]) ionic liquid was employed for dispersion of multi walled carbon nanotubes (MWCNTs) and the formation of nanocomposite on the surface of a carbon-ceramic electrode. The surface of the modified electrode was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The modified electrode exhibited excellent electrochemical activity to oxidation of dopamine (DA); whereas electro oxidation of ascorbic acid (AA) was not seen and electro oxidation of uric acid (UA) appeared at a more positive potential than DA. The multi walled carbon nanotube-ionic liquid nanocomposite modified carbon-ceramic electrode was used for the selective determination of DA in the presence of high levels of AA and UA using differential pulse voltammetry. The calibration curve for DA was linear in the range of 3.00 to 130 µM with the detection limit (S/N=3) of 0.87 µM. The present electrode was successfully applied to the determination of DA in some commercial pharmaceutical samples and human blood serum.      

Characteristics of polyurethane-based sustained release membranes for drug delivery

This paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications.      

Susceptibility to hydrolysis of phenylboronic pinacol esters at physiological pH

Boronic acids and their esters are highly considered compounds for the design of new drugs and drug delivery devices, particularly as boron-carriers suitable for neutron capture therapy. However, these compounds are only marginally stable in water. Hydrolysis of some phenylboronic pinacol esters is described here. The kinetics is dependent on the substituents in the aromatic ring. Also the pH strongly influences the rate of the reaction, which is considerably accelerated at physiological pH. Therefore, care must be taken when considering these boronic pinacol esters for pharmacological purposes.      

Inactivation of cholinesterases by silver and gold ions in vitro

The main goal of the present study was to investigate the effects of silver and gold ions on cholinesterases (ChEs) activity due to increasing application of these metals in a wide variety of nanomaterials. A chromogenic assay using the substrate o-nitrophenyl acetate/butyrate made it possible to conclude unmistakably that both metals inhibit ChEs. Addition of bovine serum albumin (BSA) indicates that binding of metal ions to albumin could serve to scavenge metals and consequently reduce their amount for reaction with ChEs. The effects of metal ions on ChE should be taken into consideration when using this enzyme as an environmental biomarker.      

Effect of hydrothermal treatment on the structure of an aluminosilicate polymer

The effect of hydrothermal treatment on the structure of an aluminosilicate polymer prepared by a polycondensation reaction between silicate and hydroxoaluminate in alkaline aqueous solution was studied. The structural changes were investigated using X-ray diffraction analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy imaging and thermogravimetric analysis. The results indicated that the amorphous aluminosilicate polymer transformed into a crystalline product during the hydrothermal treatment at 145°C. The crystalline phase was identified as a mineral of the zeolite group, most likely phillipsite. This transformation required an alkaline environment during the hydrothermal treatment.      

Simultaneous analysis of first-line anti-tuberculosis drugs in tablets by UV spectrophotometry compared to capillary zone electrophoresis

The development and optimization of a novel UV spectrophotometric methodology was proposed for simultaneous analysis of ethambutol (ETB), isoniazid (ISO), rifampicin (RIF) and pyrazinamide (PYR), using multivariate calibration based on the partial least squares method (PLS). The methodology was successfully applied for analysis of four-drug fixed dose combination (4-FDC) tablets used for tuberculosis treatment. A 3⁴ Box-Behnken design, with triplicate in central point, was used for sample preparation in the calibration step. In the present case, nine latent variables were chosen for the model development that presented the smallest RMSECV and explain 98.76% of data variance in Y block (concentrations of ETB ISO, RIF and PYR) and 99.93% of data variance in X block (spectral data). PLS models for ETB, ISO, RIF and PYR presented RMSEP and R² values of 0.23 mg L^?1 and 0.971; 0.14 mg L^?1 and 0.731; 0.11 mg L^?1 and 0.990 and 0.57 mg L^?1 and 0.972, respectively. A validation step was performed based on the comparison between the UV spectrophotometric proposed methodology and capillary zone electrophoresis (CZE) in 4-FDC real samples and no significant difference was found between two methodologies at 95% of confidence level.