Multi-residue method for trace pesticide analysis in soils by LC-QQQ-MS/MS and its application to real samples

ABSTRACT

A method for the simultaneous determination of 30 pesticides residues in soil was developed and validated. Among the studied agrochemicals, there are herbicides (auxines, sulfonylureas, fops, imidazolinones), fungicides (azoles) and insecticides (organophosphorus) widely used in extensive agricultural activities in Uruguay. Five methods with different extraction times, type and amount of solvent, as well as the possibility of a clean-up step were compared in terms of percentage of recovery and repeatability. The final method was based on the extraction of the pesticides’ residues from soil using two successive solvent extraction steps. First, the soil was extracted with methanol in an orbital shaker for 4 h. Secondly, the solid residue was re-extracted overnight with ultrapure water. The methanolic extract was concentrated under vacuum, whereas the aqueous solution was passed through an OASIS HLB® cartridge, eluted with an appropriate solvent and concentrated under nitrogen stream. Both extracts were finally combined and analysed by LC-QQQ-MS/MS using the Document SANTE/11,945/2015 criteria. Recovery percentages at 1 and 10 μg kg^?1 for the studied compounds were in the range 70106% with relative standard deviations below 19 %. The quantification was performed using matrix-matched calibration curves as some compounds presented very strong signal suppression. Residuals of the matrix-matched calibration curves were below 20% for all the validated analytes. The quantification limit was1 μg kg^?1. The method also allows the screening of 11 pesticides in soil. Sixty-five real samples collected from regions where the use of pesticides is intensive were analysed. Quinclorac, tebuconazole, penoxsulam and clomazone were the most frequently pesticides detected.     

Extraction,purification by cation exchange supermacroporous cryogel and physico-chemical characterization of γ-conglutin from lupin seeds (Lupinus albus L.)

This study focused on the extraction, purification, and physicochemical characterization of γ-conglutin, a protein present in lupin seeds with properties of reducing blood glucose levels. Total protein was extracted with an alkaline-saline solvent, followed by isoelectric precipitation. Chromatographic purification of the precipitated fraction was performed using a cation exchange supermacroporous cryogel column. Electrophoresis of the eluted fraction from chromatography presented a single band of ∼48 kDa under non-reducing conditions (two bands of ∼30 and ∼17 kDa, under reducing conditions) confirming the success of the purification protocol. Liquid chromatography-tandem mass spectrometry analysis confirmed the identity of the protein as γ-conglutin. The purified γ-conglutin had an isoelectric point of 7.51, β-sheets prevailing as a secondary structure, and denaturation temperature close to 68°C. The outcome of this work showed that γ-conglutin was obtained with a high degree of purity. The proposed purification protocol is simple and can be easily scaled up.     

Development and validation of an HPLC-DAD analytical procedure for quality control of damiana (Turnera diffusa), using an antioxidant marker isolated from the plant

Damiana is a shrub used as a dietary supplement and as an additive in several foods. This report presents the first validated analytical method for QC of products made from damiana. Through bioassay-guided fractionation, the compound showing the best antioxidant activity, determined using 2,2-diphenyl-1-picryl-hydrazyl assay in TLC, was purified and identified as 8-C-beta-[6-deoxy-2-O-(alpha-1-rhamnopyranosyl)-xylo- hexopyranos-3-uloside] (Cl50 5.56 g/mL). This is the only natural source from which this compound has been reported, and has been found in all native damiana samples analyzed. Therefore, it was used as a biomarker to develop an HPLC-diode-array detection analytical procedure using the first-order derivative of the chromatograms. Separation was achieved using an AccQ Tag C18 150 x 3.9 mm (4 microm) column, with a gradient of methanol and 0.1% trifluoroacetic acid in water. The method was shown to be accurate, sensitive, and reproducible, providing a useful quantitative means to apply QC to damiana products.     

A matrix solid-phase dispersion-gel permeation chromatography-programmed temperature vaporisation-GC-MS procedure for the analysis of polycyclic aromatic hydrocarbons in mussel samples

A simultaneous matrix solid-phase dispersion extraction-gel permeation chromatography cleanup with programmed temperature vaporisation GC-MS determination is proposed for the analysis of parent and alkylated polycyclic aromatic hydrocarbons (PAHs) in mussel samples. The parameters affecting the extraction and elution efficiency were studied. Final conditions were: 0.5?g of mussel sample, 0.5?g diatomaceous earth as dispersant; and 4?g of Bio-Beads S-X3 for the gel permeation chromatography. Ethyl acetate/hexane (1:1, v/v) was selected for the elimination of the lipid fraction and the elution of PAHs. The detection and quantification limits achieved with this procedure were between 0.01?μg/kg and 0.67?μg/kg and 0.02?μg/kg and 1.93?μg/kg, respectively. The linearity of the method ranged between 5?μg/kg and 1000?μg/kg for most of the studied PAHs. The method was validated by the analysis of mussel tissue reference material (SRM 2977). The repeatability, intermediate precision and accuracy of the method obtained are in excellent agreement with the certified values. The proposed method is simple, precise and robust; no special instruments or costly equipment are required, and a reduction in the total time of analysis, sample handling and solvent consumption is achieved in comparison with classic procedures.     

Synthesis and characterization of large colloidal cobalt particles

Large colloidal environmentally stable silica-coated cobalt particles were synthesized by combining the sodium borohydride reduction in aqueous solution and the St?ber method. Low size polydisperse cobalt spheres with an average size of 95 nm were synthesized by using a borohydride reduction method and were subsequently coated with a thin layer of silica by means of hydrolysis and condensation of tetraethylorothosilicate (TEOS) in an aqueous/ethanolic solution. The large uniform cobalt spheres consist of smaller metallic Co clusters, explaining the superparamagnetic behavior of the spheres. The particles were investigated by transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM).     

Determination of solute partition behavior with room-temperature ionic liquid based micellar gas-liquid chromatography stationary phases using the pseudophase model

The use of micelles in ionic liquid based gas-chromatography stationary phases was evaluated using equations derived for a "three-phase" model. This model allows the determination of all three partition coefficients involved in the system, and elucidates the micellar contribution to retention and selectivity. Four types of micellar-ionic liquid columns were examined in this study: 1-butyl-3-methylimidazolium chloride with sodium dodecylsulfate or dioctyl sulfosuccinate, and 1-butyl-3-methylimidazolium hexafluorophosphate with polyoxyethylene-100-stearyl ether or polyoxyethylene-23-lauryl ether. The partition coefficients were measured for a wide range of probe molecules capable of a variety of types and magnitudes of interactions. In general, most probe molecules preferentially partitioned to the micellar pseudophase over the bulk ionic liquid component of the stationary phase. Therefore, addition of surfactant to the stationary phase usually resulted in greater solute retention. It is also shown that the selectivity of the stationary phase is significantly altered by the presence of micelles, either by enhancing or lessening the separation. The effects of surfactant on the interaction parameters of the stationary phase are determined using the Abraham solvation parameter model. The addition of sodium dodecylsulfate and dioctyl sulfosuccinate to 1-butyl-3-methylimidazolium chloride stationary phases generally increased the phase's hydrogen bond basicity and increased the level of dispersion interaction. Polyoxyethylene-100-stearyl ether and polyoxyethylene-23-lauryl ether surfactants, however, enhanced the pi-pi/n-pi, polarizability/dipolarity, and hydrogen bond basicity interactions of 1-butyl-3-methylimidazolium hexafluorophosphate to a greater degree than the ionic surfactants with 1-butyl-3-methylimidazolium chloride. However, these nonionic surfactants appeared to hinder the ability of the stationary phase to interact with solutes via dispersion forces. Therefore, it is possible to effectively predict which analytes will be most highly retained by these micellar-ionic liquid stationary phases.     

Surface enhanced second harmonic generation from macrocycle, catenane, and rotaxane thin films: experiments and theory

Surface enhanced second harmonic generation (SE SHG) experiments on molecular structures, macrocycles, catenanes, and rotaxanes, deposited as monolayers and multilayers by vacuum sublimation on silver, are reported. The measurements show that the molecules form ordered thin films, where the highest degree of order is observed in the case of macrocycle monolayers and the lowest in the case of rotaxane multilayers. The second harmonic generation activity is interpreted in terms of electric field induced second harmonic (EFISH) generation where the electric field is created by the substrate silver atoms. The measured second order nonlinear optical susceptibility for a rotaxane thin film is compared with that obtained by considering only EFISH contribution to SHG intensity. The electric field on the surface of a silver layer is calculated by using the Delphi4 program for structures obtained with TINKER molecular mechanics/dynamics simulations. An excellent agreement is observed between the calculated and the measured SHG susceptibilities.     

Modulating the rate of a native ligation coupling between tripyrrole derivatives by using specific dsDNA sequences

The intrinsic recognition code associated with dsDNA allows either accelerating or retarding of a native chemical ligation reaction between tripyrrole ligands. The rate changes most probably stem from the sequence-dependent characteristics of the dsDNA-ligand complexes.     

In Line Monitoring of VAc-BuA Emulsion Polymerization Reaction in a Continuous Pulsed Sieve Plate Reactor using NIR Spectroscopy

Summary: This work deals with the in line and in situ monitoring of the changes in residual monomer concentrations and polymer particle size in the process of emulsion copolymerization of vinyl acetate (VAc) and butyl acrylate (BuA) over the sections of a novel tubular reactor (pulsed sieve plate continuous reactor, PSPC) using NIR spectroscopy. Off-line measurements (gas chromatographic, gravimetric and dynamic light scattering) were used as reference for the development of the multivariate PLS calibration model. All NIR spectra were on-line collected with an IFS 28/N Bruker spectrometer using a probe (transflectance mode) immersed into the reaction medium. The calibration model and validation data were analyzed using the OPUS/QUANT software. The results indicated that there exists a good agreement between values from the NIR calibration models and the off-line reference measured experimental data. Moreover, the on-line NIR can detect efficiently the occurrence of disturbances during the polymerization reaction, a useful tool for the improving the process safety.     

Synthesis, structure and catalase-like activity of dimanganese(III) complexes of 1,5-bis(X-salicylidenamino)pentan-3-ol (X = 3- and 5-methyl). Influence of phenyl-ring substituents on catalytic activity

The diMn(III) complexes [Mn2(5-Me-salpentO)(mu-MeO)(mu-AcO)(H2O)Br] (1) and [Mn2(3-Me-salpentO)(mu-MeO)(mu-AcO)(MeOH)2]Br (2), where salpentOH = 1,5-bis(salicylidenamino)pentan-3-ol, were synthesised and structurally characterized. The two complexes include a bis(micro-alkoxo)(micro-acetato) triply-bridged diMn(III) core with an Mn...Mn separation of 2.93-2.94 A, the structure of which is retained upon dissolution. Complexes 1 and 2 show catalytic activity toward disproportionation of H2O2, with first-order dependence on the catalyst, and saturation kinetics on [H2O2], in methanol and DMF. In DMF, the two complexes are able to disproportionate at least 1500 eq. of H2O2 without significant decomposition, while in methanol, they rapidly lose activity with formation of a non-coupled Mn(II) species. Electrospray ionisation mass spectrometry, EPR and UV/vis spectroscopy used to monitor the reaction suggest that the major active form of the catalyst occurs in the Mn2(III) oxidation state during cycling. The correlation between log(k(cat)) and the redox potentials of 1, 2 and analogous complexes of other X-salpentOH derivatives indicates that, in this series, the oxidation of the catalyst is probably the rate-limiting step in the catalytic cycle. It is also noted that formation of the catalyst-peroxide adduct is more sensitive to steric effects in DMF than in methanol. Overall, kinetics and spectroscopic studies of H2O2 dismutation by these complexes converge at a catalytic cycle that involves the Mn2(III) and Mn2(IV) oxidation states.