Utilisation of liquid chromatography in aquatic photodegradation studies of pesticides: A comparison between distilled water and seawater

Summary The advantages of liquid chromatography with diode array and mass spectrometric detection are described for the direct characterization of the photodegradation products of Fenitrothion, Atrazine and Diuron in distilled water and artifical seawater samples. The photodegradation (UV >290 nm) of the herbicides Atrazine and Diuron was examined in distilled water and in artificial seawater containing humic acids. Major photodegradation products were hydroxyatrazine and Monuron, respectively. The results showed a faster degradation in seawater as compared to distilled water for Atrazine whereas for Diuron a quenching effect was observed thus retarding photodegradation. The photodegradation of Fenitrothion was also investigated. For this pesticide, hydrolysis predominates in seawater and photolysis is very slow in distilled water, so that acetone was needed as photosensitizer.Presented at the 5th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region, Blanes, Spain, 2–6 October, 1989.     

Phenylurea and Triazine Herbicides in the Garonne River (France) During High Flood and Low Water Periods

Abstract

Phenylureas and triazines were analysed by reversed-phase liquid chromatography using UV detection at 254 nm after an on-line preconcentration step on a PRP-1 copolymer in order to determine pesticides in river water at μg/1 level or lower. Running water was sampled in the Garonne from a station located at La Réole, upstream from Bordeaux and from a small tributary, the Dropt. Water samples were collected mainly at several periods between December 1989 and September 1990 at a low water time (December 1989) and during two high flood periods (February 1990 and May 1990). Atrazine, simazine, de-ethylatiazine, diuron, chlortoluron and isoproturon were detected and quantified. In the Garonne river, atrazine, simazine, de-ethylatrazine and diuron were usually present at the sampling time, whereas chlortoluron and isoproturon maximised during the winter flood (February). In the Dropt river, triazine concentrations were normally between 1.0 and 0.1 μg/1 and maximised at 2.2 μg/1 during the spring flood (June 1990). De-ethylatrazine/(Atrazine + Simazine) ratio seems to be significantly higher than in the Mississippi river and may be in relation to the use of simazine in the drainage basin. These data are in agreement with seasonal applications of phenylurea and triazine herbicides and hydrologic and pluviometric conditions.     

Comparative photodegradation study of atrazine and desethylatrazine in water samples containing titanium dioxide/hydrogen peroxide and ferric chloride/hydrogen peroxide

Results are reported for a comparative photodegradation study of atrazine and desethylatrazine in water using TiO2/H2O2, FeCl3/H2O2, and photolysis. Deionized water and ground water spiked with atrazine or desethylatrazine at 36 micrograms/L were irradiated by using a xenon arc lamp and/or sunlight. After irradiation, the water samples containing the spiked pesticides were preconcentrated by using C18 solid-phase extraction disks and analyzed by gas chromatography with nitrogen-phosphorus and mass spectrometric detection. A relative percentage of 7% desethylatrazine was detected in samples removed after 20 and 4 min of sensitized photodegradation with TiO2 and Fe3+, respectively. Atrazine and desethylatrazine did not degrade when solar irradiation (in winter) and deionized water were used. Atrazine degraded faster than desethylatrazine when a xenon arc lamp or sunlight plus FeCl3 was used, with half-lives varying from 5 to 11 min and from 19 to 26 min, respectively. In other photodegradation experiments, the degradation of atrazine was slightly higher than that of desethylatrazine. This study shows that desethylatrazine has slightly higher stability than atrazine in environmental water samples; this stability accounts for the frequent detection of desethylatrazine together with atrazine in natural waters.     

Univariate method for background correction in liquid chromatography-Fourier transform infrared spectrometry

An univariate method is proposed for background correction in on-line gradient liquid chromatography-Fourier transform infrared (LC-FTIR) spectrometry using acetonitrile:water as mobile phase components. The method is based on the calculation of the ratio of absorbances (AR) at two characteristic wavenumbers for each spectrum. This parameter is subsequently used to locate the most appropriated eluent spectrum within a reference spectra matrix (RSM) to be subtracted from each spectrum included in the sample chromatogram. To correct minor changes in eluent spectra intensity during the elution of analytes, a correction factor (Kf), defined as the ratio of the absorbance of the sample and the selected eluent spectrum at a defined wavenumber was determined. The performance of the procedure was evaluated by correcting an on-line gradient LC-FTIR injection of a mixture of two pesticides (Atrazine and Diuron). Using the AR of the absorbance at 2248.6 and 2256.3 cm(-1) and a Kf at 2248.6 cm(-1), the correlation factors between FTIR spectra extracted at the peak apex from the LC-FTIR chromatogram and those obtained from pure pesticide standards were 0.975 and 0.94 for Atrazine and Diuron, respectively.     

Synthesis of a molecularly imprinted polymer on mSiO2@Fe3O4 for the selective adsorption of atrazine

Atrazine contamination of water is of considerable concern because of the potential hazard to human health. In this study, a magnetic molecularly imprinted polymer for atrazine was prepared by the surface‐imprinting technique using Fe₃O₄ as the core, mesoporous silica as the carrier, atrazine as the template, and itaconic acid as the functional monomer. The magnetic molecularly imprinted polymer was characterized by Fourier‐transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, and vibration‐sample magnetometry. The binding properties of the magnetic molecularly imprinted polymer toward atrazine were investigated by adsorption isotherms, kinetics, and competitive adsorption. It was found that the adsorption equilibrium was achieved within 2 h, the maximum adsorption capacity of atrazine was 8.8 μmol/g, and the adsorption process could be well described by the Langmuir isotherm model and pseudo‐second‐order kinetic model. The magnetic molecularly imprinted polymer exhibited good adsorption selectivity for atrazine with respect to structural analogues, such as cyanazine, simetryne, and prometryn. The reusability of the magnetic molecularly imprinted polymer was demonstrated for at least five repeated cycles without a significant decrease in adsorption capacity. These results suggested that the magnetic molecularly imprinted polymer could be used as an efficient material for the selective adsorption and removal of atrazine from water samples.     

Free energy perturbation study of water dimer dissociation kinetics

An efficient approach is described for using accurate ab initio calculations to determine the rates of elementary condensation and evaporation processes that lead to nucleation of aqueous aerosols. The feasibility of the method is demonstrated in an application to evaporation rates of water dimer at 230 K. The method, known as ABC-FEP (ab initio/classical free energy perturbation), begins with a calculation of the potential of mean force for the dissociation (evaporation) of small water clusters using a molecular dynamics (MD) simulation with a model potential. The free energy perturbation is used to calculate how changing from the model potential to a potential calculated from ab initio methods would alter the potential of mean force. The difference in free energy is the Boltzmann-weighted average of the difference between the ab initio and classical potential energies, with the average taken over a sample of configurations from the MD simulation. In principle, the method does not require a highly accurate model potential, though more accurate potentials require fewer configurations to achieve a small sampling error in the free energy perturbation step. To test the feasibility of obtaining accurate potentials of mean force from ab initio calculations at a modest number of configurations, the free energy perturbation method has been used to correct the errors when some standard models for bulk water (SPC, TIP4P, and TIP4PFQ) are applied to water dimer. To allow a thorough exploration of sampling issues, a highly accurate fit to results of accurate ab initio calculations, known as SAPT-5s, as been used a proxy for the ab initio calculations. It is shown that accurate values for a point on the potential of mean force can be obtained from any of the water models using ab initio calculations at only 50 configurations. Thus, this method allows accurate simulations of small clusters without the need to develop water models specifically for clusters.     

Voltammetric method for direct determination of nickel in natural waters in the presence of surfactants

Voltammetric procedures for direct Ni(II) determination in natural water samples are described. The procedures are based on nickel deposition to the metallic state and then its oxidation in the presence of dimethylglyoxime with the formation of the complex adsorbed on the electrode. Reduction of the complex is exploited in the detection step. Due to the application of a sufficiently negative deposition potential the interference from surfactants is minimized. The detection limits for Ni(II) are 2x10(-9) and 2x10(-10) mol l(-1) for deposition times of 30 and 120 s, respectively. The influence of foreign ions is also presented.     

Sensitive SPE GC-MS-SIM screening of endocrine-disrupting herbicides and related degradation products in natural surface waters and robustness study

This paper describes a very sensitive capillary gas chromatographic mass spectrometric selective ion monitored method for the simultaneous determination of three chloro-s-triazine herbicides, Atrazine (AT), Simazine (SI) and Propazine (PP), three thiomethyl-s-triazine ones: Ametryn (AM), Prometryn (PM) and Terbutryne (TB) and three chloro-s-triazine degradation products, Deethyl-atrazine (DEA), Deisopropyl-atrazine (DIA) and Deethyldeisopropyl-atrazine (DD) with herbicide activity too. The instrumental parameters affecting GC separation and MS/SIM detection were investigated and from this study the best conditions were selected. A previous extraction and preconcentration step was applied by means of an off-line solid phase extraction process getting so an enrichment factor of 10⁴. The analytical performance characteristics of our method (stability, precision, linearity, LODs, LOQs, accuracy and robustness) were evaluated by means of a validation study on tap and deionised water samples using di-phenyl amide (DPA) as internal standard to achieve quantification. Natural water samples from different locations suspected to contamination were analysed by this off line SPE-GC-MS-SIM procedure and the results were also confirmed by an HPLC method.     

Equivalent potential of water for electronic structure of asparagine

The equivalent potential of water for the electronic structure of asparagine(Asn) is constructed by using the first‐principles, all‐electron, ab initio calculation. The process is composed of three steps. The first step is to determine the geometric structure of Asn+nH₂O system with a minimum energy. The second step is to calculate the electronic structure of Asn with the potential of water molecules by using the self‐consistent cluster‐embedding (SCCE) method, based on the result obtained in the first step. The last step is to calculate the electronic structure of Asn with the potential of dipole after replacing water molecules with dipoles. The results show that the major effect of water molecules on Asn' electronic structure be raising the occupied electronic states by 0.034 Ry on average and narrowing energy gap by 0.91%. The effect of water on the electronic structure of Asn can be well simulated by using dipole potential. The obtained equivalent potential can be applied directly to the electronic structure calculation of protein in solution by using the SCCE method. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Preparation and characterization of dicarboxylic acid modified starch-clay composites as carriers for pesticide delivery

Modified starch based composites were prepared with bentonite/organobentonite for their potential use as carriers for pesticide delivery. Soluble starch was esterified with dicarboxylic acid chlorides. Mean degree of substitution of modified starches varied from 0.101 to 0.353. Composites were prepared by solution intercalation method using these esterified starches and bentonite or cetyltrimethylammonium bentonite as filler materials. TEM analysis of composites showed well exfoliated/intercalated structures. Atrazine as a model pesticide was encapsulated in them and encapsulation was found to be 83.52–92.83%. These composites were also found to be acted as controlled release matrices for atrazine and release pattern was diffusion controlled. As compared to the commercially available wettable powder formulation, the composites were able to release encapsulated atrazine in water for a longer period. The research showed that the prepared composites could be further investigated as carriers for controlled release formulations of pesticides to minimize dose and number of applications.     

A simple method for the spectrophotometric determination of atrazine using p-aminoacetophenone and its application in environmental and biological samples

A spectrophotometric method is described for the determination of the widely used herbicide, atrazine. Atrazine reacts with pyridine and forms a quaternary halide which adds a hydroxyl group in the presence of alkali to form a carbinol base. The heterocyclic ring of the resulting carbinol breaks forming a glutaconic dialdehyde which is subsequently coupled with p-aminoacetophenone (PMP) to form a yellow orange polymethine dye. Beer's law is obeyed in the range 0.16–1.6 ppm of atrazine at 470 nm. The method is sensitive and free from the interference of most of the foreign species. The analytical parameters have been optimised and the method has been successfully applied to the determination of atrazine in various environmental and biological samples.     

Comportement polarographique et solvatation de quelques cations dans le mélange binaire diméthylsulfoxyde-carbonate de propylène

The electrochemical oxidation of 2,4,6-tri-tert-butylphenol as well as the phenoxide and phenoxy radical derived from it has been investigated in acetonitrile and ethanol+water. The ease of oxidation decreases in the order phenoxide, phenoxy radical, phenol with the separation between potentials for phenoxide oxidation and phenoxy radical oxidation being 1.2 V in acetonitrile. The phenoxide is oxidized to the stable phenoxy radical in a highly reversible reaction in acetonitrile and alkaline ethanol+water. Oxidation of the radical produces a phenoxonium ion which is attacked by water giving 2,4,6-tri-tert-butyl-4-hydroxy-2,5-cyclohexadienone. This two electron product is also formed upon oxidation of the phenol in either solvent. However, in acidic media the hydroxydienone dealkylates give 2,6-di-tert-butylhydroquinone which is oxidized to the final product 2,6-di-tert-butyl-1,4-benzoquinone. The dealkylation is quite rapid in anhydrous acetonitrile but the rate is depressed by the addition of water.A novel double potential step experiment was used to characterize the oxidation of the phenoxy radical. A step to a potential where the phenoxide is oxidized to the phenoxy radical is followed by a step to a potential where the phenoxy radical is oxidized. The current during the second step is unusually small because protons produced by the oxidation of the radical deactivate the phenoxide. The current-time curve was found to agree with that predicted by digital simulation.     

气相色谱法测定水生植物中的阿特拉津残留

确立了一套检测水生植物中阿特拉津残留量的方法.样品经石油醚-二氯甲烷混合液振荡萃取,经硅镁吸附剂层析柱净化后,采用气相色谱-电子捕获检测器检测水生植物中阿特拉津的残留量.该方法在0.062～1.0mg/L范围内峰面积与阿特拉津浓度的线性关系良好(r~2=0.9993).在0.5mg/L、1.0mg/L、1.5mg/L ...     

Development of a microparticle-based on-site immunoassay for the detection of atrazine in soil and water samples

Atrazine is widely used as a herbicide in agriculture and has been identified as a major groundwater contaminant in the US. Because of the possible hazard associated with its usage, there is a need for an efficient and economic screening method for on-site field testing of atrazine and other s-triazine herbicides in soil and water. We have developed a rapid, on-site test for the detection of atrazine based on the principle of microparticle agglutination inhibition immunoassay. The test detects 50 microg kg(-1) (0.050 ppm) atrazine in soil samples with direct extraction and 1.0 microg L(-1) atrazine in water samples when coupled with solid phase extraction.     

A New Versatile Water‐Soluble Iniferter Platform for the Preparation of Molecularly Imprinted Nanoparticles by Photopolymerisation in Aqueous Media

The multi‐step synthesis of a new water‐soluble dithiocarbamate iniferter platform for the preparation of nanoparticles and ‐gels in aqueous solvents by photoinduced living‐radical polymerisation is described herein. The water solubility of the dithiocarbamate iniferter was achieved by incorporating two unprotected glucose units into the iniferter structure by copper(I)‐catalysed azide–alkyne cycloaddition (“click chemistry”). Molecularly imprinted nanoparticles (MIPs) specific for 2,4‐dichlorophenoxyacetic acid and the corresponding non‐imprinted particles (NIPs) were prepared in pure water by using the prepared iniferter as photoinitiator. Radioligand binding tests confirmed a high imprinting factor, and the living character of the iniferter was demonstrated by re‐initiating a second photochemical polymerisation on the NIP nanoparticles in water by using ethylene glycol methacrylate phosphate. Our newly synthesised structure is a promising tool for iniferter‐mediated photopolymerisations in aqueous media for the preparation of biocompatible nanomaterials with high potential for biomedical applications in a bottom‐up fashion.     

Hydroxide oxidation and peroxide formation at embedded binuclear transition metal sites; TM = Cr, Mn, Fe, Co

Key steps in electro-catalytic water oxidation on binuclear Transition Metal (TM) sites are addressed. These comprise (a) two one-electron oxidation steps of TM-OH moieties to form the corresponding two TM=O oxy-groups, and (b) a chemical step whereby the two oxy-species form a TM-O-O-TM peroxy-bridge. A test rig representing a generic low crystal field oxide support is described and employed. The energetics for homo-nuclear Cr(III-V), Mn(III-V), Fe(II-IV) and Co(II-IV) sites are compared. The uniqueness of the tyrosine/tyrosyl-radical (TyrOH/TyrO˙) reference potential for driving the oxidation steps is demonstrated. The oxidation of adsorbed TM-OH moieties on binuclear Mn and Co candidates requires an overpotential of approximately 0.5 V relative to the chosen reference potential. Correspondingly, the subsequent O-O bond formation becomes strongly exothermic, of the order of 1 eV. The hydroxide oxidation steps on binuclear CrCr and FeFe systems are, in total, exothermic by 1.21 and 0.61 eV, respectively, relative to the TyrOH/TyrO˙ reference potential. Consequently, the chemical step for transforming the TM=O moieties to the peroxo species is found to be endothermic by the order of 0.7 eV. Based on these findings, a catalyst containing one TM from each class is suggested. The validity of this concept is demonstrated for the FeCo binuclear site. The results are discussed in the context of experimental observations, which display a preference for mixed oxide systems.     

Vertical Mobility of Soil Contaminants: Preliminary Results of a Survey on the Herbicide Atrazine

Abstract

Atrazine is considered a potential contaminant of water bodies, where it has been repeatedly detected. Its use in Italy is almost limited to the Northern part of the country where corn monocultures are common. Northern Italy is characterized by the presence of an area with soil quite permeable and where ground waters are often present at not very deep levels. In this area well waters, which represent the main source of drinking water, have been frequently found contaminated by atrazine. A program has been started aimed at studying the role of soil nature and local factors in the process of groundwater contamination. Two atrazine application rates were used at two sites with loamy and loamy-sandy soils. Results clearly show a different mobility of atrazine in the two soil types. Since the two sites have similar organic carbon levels, the major proportion of clay to sand and the lower pH of loamy soil may explain the lower vertical mobility of atrazine in this soil. Work is in progress to study atrazine behaviour to a soil depth of 30cm and the effect of repeated atrazine applications on ground water pollution.     

Fabrication of Atrazine Molecularly Imprinted Polymer Microsphere by Two Step Seed Swelling Polymerization Method

Atrazine molecularly imprinted polymer microspheres (MIPMs) were fabricated by two step seed swelling polymerization method, using atrazine as a template molecule, methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EDMA) as a crosslinking agent and toluene/dodecanol as a porogenic agent and a series of MIPMs with even particle size of 3‐5 μm and good dispersivity could be obtained under the optimal condition. Equilibrium binding experiments were comparably studied about the binding capacity of the resulted polymers. We packed the polymers into empty chromatographic steel tube columns (2.1 mm I.D. × 10 cm) to prepare liquid chromatographic columns used for the evaluation of specificity with similar structure compounds. The proposed method has been successfully applied to the determination of limited atrazine in water samples. The results showed that a good linear relationship of atrazine was maintained within 0.1‐20 mg/L (r = 0.9992), the sample recovery was in a range of 92.1‐102.0%, with a RSD lower than 5% (n = 6) and a detection limit of 0.041 mg/L.     

Mixed-level orthogonal array design for the optimization of solid-phase extraction of some pesticides from surface water

An orthogonal array design (OAD), OA32(4(1) x 2(28)), was employed as a chemometric method for the optimization of the solid-phase extraction (SPE) of atrazine, diazinon, ametryn and fenthion in surface water. Seven parameters: the type of eluting solvent, type of sorbent, flow-rate of eluting solvent, sample pH, sample volume, elution volume, addition of modifier and flow-rate of water sample were studied and optimized by a mixed-level OAD. The effects of these factors and some two-variable interactions on the recovery of the pesticides were quantitatively evaluated by the analysis of variance and percentage contribution techniques. The final optimized condition was employed for the SPE of selected micro-organic pollutants from Karoun river water, south of Iran. Atrazine and ametryn were tentatively identified and determined at the 0.7 and 0.9 microg l(-1) level, respectively.     

Homogeneous immunoassay of atrazine in water by terbium-entrapping liposomes as fluorescent markers

Atrazine (Atr) was conjugated to mastoparan (Mast) cytolytic peptide; Mast-Atr derivative was used as cytolytic agent on liposomes trapping Tb/citrate complex. This was applied in a time-resolved fluoroimmunoassay for detection of Atr in water. The cytolytic activity was read by means of time-resolved fluorescence after adding an excess of dipicolinic acid (DPA). Tb/citrate-entrapping liposomes are easy to prepare, and the assay is carried out in a short incubation time and in a range between 10 pg and 100 ng. The procedure was applied to analyse samples taken from Adda River and from irrigation ditches in an agricultural area around the town of Lodi. Recovery in samples spiked with two different Atr concentrations was between 95 and 105%.