Removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions by partially characterized organophilic sepiolite: thermodynamic and kinetic calculations

The adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) on organophilic sepiolite (dodecylammonium sepiolite, DAS) was studied as a function of solution concentration and temperature. The observed adsorption rates were found to be equal to the first-order kinetics. The rate constants were calculated for temperatures ranging between 25 and 40 degrees C at constant concentration. The adsorption energies, E, and adsorption capacity, q(m), for 2,4-D adsorption on organophilic sepiolite was estimated using the Dubinin-Radushkevic equation. Thermodynamic parameters (Deltag(a), Deltah(a), Deltas(a)) were determined by a new approximation from the isotherm of 2,4-D adsorption on DAS. Also, DeltaS(0) and DeltaH(0) values were calculated from the van't Hoff equation. These isotherms were modeled according to the Freundlich and Dubinin-Radushkevic adsorption equations. The amount of adsorption of this herbicide on organophilic sepiolite was found to be dependent on the relative energies of adsorbent-adsorbate, adsorbate-solvent, and adsorbate-adsorbate interaction.     

Characterization and adsorption properties of tetrabutylammonium montmorillonite (TBAM) clay: thermodynamic and kinetic calculations

The montmorillonite has been subjected to modification through ion-exchange reaction by tetrabutylammonium bromide (TBAB). The modified sample was studied by X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) methods. The basal spacing of modified montmorillonite was determined as 14.40 A. The IR spectra of modified montmorillonite showed CH vibrations. The characterization of tetrabutylammonium montmorillonite (TBAM) and the adsorption of p-chlorophenol (p-CP) on organomontmorillonite was studied as a function of the solution concentration and temperature. The observed adsorption rates were found to fit to the pseudo-second-order kinetics. The rate constants were calculated for temperatures ranging between 25.0-35.0 degrees C at constant concentration. The adsorption energy, E, and adsorption capacity, (q(m)), for phenolic compounds adsorbing on organomontmorillonite were estimated using the Dubinin-Radushkevich (D-R) equation. Thermodynamic parameters (delta g(a) = -11.063 and -11.802 kJ/mol, delta h(a) = -30.032 and -30.789 kJ/mol, delta s(a) = -0.0636 and -0.0637 kJ/mol K for 298 and 308 K, respectively) were calculated by a new approximation from the adsorption isotherms of p-CP on organomontmorillonite. These isotherms were modeled according to Freundlich and Dubinin-Radushkevich adsorption isotherms, through which the first-order and second-order coefficients (K(1ads) = 0.0152 and 0.0127 micromol/g min, K(2ads) = 0.0130 and 0.0108 L/min micromol, respectively) were obtained at 298 and 308 K.     

Optimizing Separation Conditions for Chlorophenoxycarboxylic Acid Herbicides in Natural and Potable Water Using Capillary Zone Electrophoresis

Chlorophenoxycarboxylic acid herbicides were separated and determined by capillary electrophoresis. An analysis of a six-component mixture containing 2,4-dichlorophenoxybutyric (2,4-DB), 2,4-dichlorophenoxypropionic (2,4-DP), 2,4,5-trichlorophenoxyacetic (2,4,5-T), 2,4-dichlorophenoxyacetic (2,4-D), and phenoxyacetic (PA) acids and 2,4-dichlorophenol (2,4-DCP), the product of their degradation in aqueous media, took no longer than 15 min. Solid-phase extraction on Diapak C-16 cartridges was used for sample preparation. The detection limits for herbicides in water samples with account for preconcentration (K = 250) were found to be 0.0005 mg/L for 2,4-DB, 2,4-DP, 2,4,5-T, and 2,4-D and 0.001 mg/L for PA. It was shown that humic acids (< 50 mg/L) do not interfere with the determination of chlorophenoxycarboxylic acids.     

A Method for Determination of Low Levels of Exposure to 2,4-D and 2,4,5-T

A method has been developed for the determination of trace quantities of 2,4-dichloro-phenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2,4-dichlorophenol (2,4-DCP), and 2,4,5-trichlorophenol (2,4,5-TCP) in human and rat urine. The method involves acid hydrolysis of the phenolic conjugates, extraction of the free phenols and acids, ethylation with diazoethane, silica-gel column chromatography clean-up of the derivatized urine extract, and gas chromatographic determination using the electron-capture detector. The average recoveries of 2,4-D, 2,4,5-T, 2,4-DCP, and 2,4,5-TCP from rat urine spiked with known amounts of the herbicides and their phenols were 94%, 98%, 92%, and 90%, respectively. The limits of detection for 2,4-D, 2,4,5-T, DCP, and TCP in rat urine were: 0.05, 0.01, 0.10, and 0.01 ppm, respectively. The method was used to analyze urine of rats given various levels of 2,4-D and 2,4,5-T by gavage. Results showed that levels of exposure of 3.75 mcg/kg for 2,4-D and 5.0 mcg/kg for 2,4,5-T in rats can be detected in urine within 24 hr from exposure. Urine samples from occupationally exposed people were analyzed and found to contain 0.2 to 1.0 ppm 2,4-D and 0.05 to 3.6 ppm 2,4,5-T.     

Sorption behavior of acidic herbicides on carbon nanotubes

Carbon nanotubes and graphitized carbon are investigated as adsorbents for solid phase extraction of dicamba and 2,4,5-T, two phenoxyalkanoic acid herbicides. These adsorbents have much greater adsorption capability than that of C₁₈ bonded silica, which was also tested for comparison studies. The adsorption capacity increases remarkably at lower pH of the sample solution. Freundlich isotherms were applied to analyze the data. Our studies suggest that carbon nanotubes have great potential applications in environmental analysis.     

Separation and determination of 2,4-D, dicamba and 2,4,5-T in tobacco by nonaqueous capillary electrophoresis

A practical method for residue analysis of 2,4-D, dicamba and 2,4,5-T in baked tobacco leaves has been developed using nonaqueous CE (NACE). The herbicide residues of 2,4-D, dicamba and 2,4,5-T in tobaccos were extracted by ultrasonication with ethyl acetate, followed by a cleanup procedure with gel permeation chromatography. The separation of 2,4-D, dicamba and 2,4,5-T by NACE was optimized based on orthogonal experiment design with four factors at three levels. The optimal NACE condition was established with the running buffer of 40.0 mmol/L ammonium acetate in 90% CH3CN (apparent pH 10.2), and the applied voltage of -25 kV over a capillary of 50 microm id x 46 cm (37.5 cm to the detector window), which gave a baseline separation of 2,4-D, dicamba and 2,4,5-T within 15 min. The LOD were ca. 0.4-0.6 microg/mL for the three herbicides, whereas the overall recovery ranged from 80.8 to 84.1%. The proposed method has been successfully applied to measure 300 real tobacco samples, and the residue profiles of the three herbicides in tobacco samples were obtained and evaluated.     

Solid-phase extraction of acidic herbicides

A discussion of solid-phase extraction method development for acidic herbicides is presented that reviews sample matrix modification, extraction sorbent selection, derivatization procedures for gas chromatographic analysis, and clean-up procedures for high-performance liquid chromatographic analysis. Acidic herbicides are families of compounds that include derivatives of phenol (dinoseb, dinoterb and pentachlorophenol), benzoic acid (acifluorfen, chloramben, dicamba, 3,5-dichlorobenzoic acid and dacthal--a dibenzoic acid derivative), acetic acid [2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)], propanoic acid [dichlorprop, fluazifop, haloxyfop, 2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and silvex], butanoic acid [4-(2,4-dichlorophenoxy)butanoic acid (2,4-DB) and 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB)], and other miscellaneous acids such as pyridinecarboxylic acid (picloram) and thiadiazine dioxide (bentazon).     

Adsorption of Pesticides on Soil Components

The adsorption of two pesticides (2,4-phenoxy acetic acid (2,4D) and thiabendazol) on silica, alumina, kaolin and montmorillonite is studied from adsorption isotherms and enthalpies. 2,4D is not adsorbed by silica, kaolinite and montmorillonite even in the presence of 0.01 mol l?1 divalent cations. On alumina, the energy of adsorption is comparable with that of the formation of an acid-base complex. Thiabendazol can be adsorbed on silica and clays from an ethanol solution. Most adsorption isotherms are of the Langmuir type and correspond to roughly constant adsorption enthalpies as a function of coverage except for kaolin where adsorption on both lateral and basal faces can be involved. Adsorption after introducing humic acids to the system was also studied for kaolin.     

Characterization and determination of the thermodynamic and kinetic properties of p-CP adsorption onto organophilic bentonite from aqueous solution

The characterization of tetraethylammonium bentonite and the adsorption of p-chlorophenol (p-CP) onto organophilic bentonite (tetraethylammonium bentonite) was studied as a function of the solution concentration and temperature. The observed adsorption rates were found to fit first-order kinetics. The rate constants were calculated for temperatures ranging between 15.0 and 35.0 degrees C at constant concentration. The adsorption energy E and adsorption capacity q(m) for the phenolic compound adsorbing on organophilic bentonite were estimated using the Dubinin-Radushkevic equation. Thermodynamic parameters (Deltag(a), Deltah(a), Deltas(a)) were calculated by a new approximation from the isotherms of p-CP adsorption on organophilic bentonite. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms. The amount of adsorption of p-chlorophenol on organophilic bentonite was found to be dependent on the relative energies of adsorbent-adsorbate, adsorbate-solvent, and adsorbate-adsorbate interactions.     

Plain Thin-layer Chromatography of Some Herbicides and Related Compounds on Admixture of Barium Sulfate and Calcium Sulphate in Mixed Solvents

Abstract

Some carboxylic herbicides and plant growth regulators such as benzoic acid, 4-chlorophenoxyacetic acid, cinnamic acid, 2,4-D, indole-3-acetic acid, indolepropionic acid, α-naphthalleneacetic acid, β-naphthal eneacetic acid, β-naphthoxyacetic acid, phenoxyacetic acid, TCA and 2,4,5-T have been separated on BaSO₄-CaSO₄ (1:1) coatings in mixed solvent systems.

Quantitative separations of indole-3-acetic acid (100 μg) from 50–100 μg of benzoic acid, α-naphthaleneacetic acid and 2,4,5-T have been carried out successfully.     

Preliminary Screening Method for Dioxin Contamination Using Polarization Fluoroimmunoassay for Chlorinated Phenoxyacid Pesticides

Polarization fluoroimmunoassays (PFIA) were developed for the chlorinated pesticides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). In order to optimize the PFIA procedures, a number of fluorescein-labeled 2,4-D and 2,4,5-T derivatives were synthesized and the influence of their structures on PFIA characteristics was studied. Also, several antisera were tested in developing the PFIA for 2,4,5-T. The assays were adapted for use with the Abbott TDx Analyzer and could be run in automatic mode by the adaptation of existing software and protocols. Dynamic ranges for 2,4-D and 2,4,5-T were 0.2-200 ng mL^–1 and 30-10 000 ng mL^–1, respectively. Total time for the automated assay of 20 samples was about 22 min. PFIA provides a suitable means for screening of a large number of samples. The rapid determination of 2,4,5-T, which is one of the precursors of polychlorinated dibenzo-p-dioxins, one of the most toxic groups of pollutants, may potentially be used to provide preliminary evidence of dioxin contamination.     

Behaviour of Phenoxyacetic Acids During Underground Passage with Different Redox Zones

Abstract

The behaviour of the three phenoxyacetic acid herbicides 2,4-D, 2,4,5-T and MCPA during underground passage and bankfiltration was tested in a model system consisting of laboratory filter columns filled with natural underground materials. Different redox environments were reproduced by operating the filters with natural aerobic and anaerobic groundwater. In the presence of oxygen, biodegradation of the three herbicides started after a lag phase. Under sulfate reducing conditions, no degradation could be observed. To assess the factors that may influence microbial degradation in the anaerobic environment, the concentration of herbicides, the time and the nutrient content were varied, but this did not increase degradation. The maximum retention of the herbicides in the filters was 30%, mainly due to adsorption to the filter material.     

Separation and identification of some chlorinated hydrocarbon insecticides and herbicides by two-dimensional thin-layer chromatography

Summary A simple and rapid procedure for the two-dimensional TLC separation and identification of some chlorinated insecticides and herbicides is described. The separation is carried out on silica gel G with the following solvent systems: a) benzene-glacial acetic acid-n-hexane and b) petroleum fraction b.p. 80–100°C. The identification is achieved by spraying the chromatogram with diphenylamine and irradiating with U.V. light. The following pesticides were used in the procedure: aldrin, isodrin, dieldrin, endrin, p,p-DDT, p,p-DDE, lindane, toxaphene, methoxychlor, 2,4-dichlorophenoxyacetic acid (2,4-D), 4-(2,4-dichlorophenoxyacetic acid)-butyl ester (2,4-DB), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 4-chloro-2-methylphenoxyacetic acid (MCPA), 4-chlor-2-methylphenoxypropionic acid (MCPP) and dalapon. The herbicides 2,4-DB and MCPP could not be separated.

---

Zusammenfassung Eine einfache und schnelle Methode zur zweidimensionalen dünnschichtchromatographischen Trennung und Identifizierung chlorierter Insecticide und Herbicide wird beschrieben. Die Trennung wird auf Silicagel G mit Benzol-Eisessig-n-Hexan bzw. der Benzinfraktion Kp 80–100°C durchgeführt. Die Identifizierung erfolgt durch Besprühen mit Diphenylamin und UV-Bestrahlung. Folgende Pesticide wurden untersucht: Aldrin, Isodrin, Dieldrin, Endrin, p,p-DDT, p,p-DDE, Lindan, Toxaphen, Methoxychlor, 2,4-Dichlorphenoxyessigsäure (2,4-D), 4-(2,4-Dichlorphenoxyessigsäure)-butylester (2,4-DB), 2,4,5-Trichlorphenoxyessigsäure (2,4,5-T), 4-Chlor-2-methylphenoxyessigsäure (MCPA), 4-Chlor-2-methylphenoxypropionsäure (MCPP) und Dalapon. Die Herbicide 2,4-DB und MCPP konnten nicht getrennt werden.

     

气相色谱–质谱法测定棉花中苯氧羧酸类除草剂

采用气相色谱–质谱联用法检测棉花中3种苯氧羧酸类除草剂[2,4-D,2,4,5-T,2-甲-4-氯丁酸(MCPB)]的残留量。样品用甲酸酸化的丙酮提取,硫酸催化甲酯化反应,用气相色谱–质谱联用仪测定。采用HPLC法与GC–MS法对提取与衍生化步骤进行优化。2,4-D,2,4,5-T,MCPB 3种化合物在0.075~7.5 mg/kg范围内线性均良好,检出限分别为0.5,0.5,0.8μg/kg,测定结果的相对标准偏差分别为4.1%,4.3%,4.0%(n=5),方法回收率分别为93.6%,95.5%,93.9%。该方法各项指标均可满足检测要求。     

Formation of derivatives of chlorophenoxy acids and some other herbicides

Summary A fuming sulphuric acid-ethanol esterification method has been applied to chlorophenoxy acids and some other herbicides. This method is compared with esterification by iodoethane and diazomethane. The chlorophenoxy acids studied were: 2,4-D, dichlorprop, MCPA, MCPB, mecoprop and 2,4,5-T. Other herbicides studied were: benazolin, bentazone, bromophenoxime, bromoxynil, chlorthal, dicamba, 3,6-dichloropicolinic acid, dinoseb, ethephon, fluroxypyr, glyphosate, haloxyfop, ioxynil, picloram, 2,3,6-TBA and triclopyr. Fuming sulphuric acid-ethanol esterification can be successfully applied to chlorophenoxy acids, benazolin, 3,6-dichloropicolinic acid, dinoseb, fluroxypyr, haloxyfop, picloram and triclopyr. The reproductibility of the method is ±5%.     

Sorption equilibrium prediction of competitive adsorption of herbicides 2,4-D and MCPA from aqueous solution on activated carbon using ANN

The simultaneous adsorption of two herbicides—2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA)—from their aqueous binary mixtures onto granular activated carbon was studied. The quantities adsorbed were determined by HPLC with UV detection. The experimental data were analysed using the Freundlich adsorption isotherm. The high correlation coefficients indicated that the adsorption equilibrium fitted the Freundlich isotherm well. A multilayer perceptron (MLP) (an artificial neural network model—ANN) was applied to describe the adsorption equilibrium in multicomponent systems. This enabled sorption isotherms to be predicted for all possible combinations of the two herbicides. The experimental results and the calculated data obtained from MLP for the solutions of the individual components and their mixtures suggest that MCPA is better adsorbed onto activated carbon than 2,4-D.     

Analysis of phenoxyacetic acid herbicides as biomarkers in human urine using liquid chromatography/triple quadrupole mass spectrometry

Phenoxyacetic acids are widely used herbicides. The toxicity of phenoxyacetic acids is debated, but high-level exposure has been shown to be hepatotoxic as well as nephrotoxic in animal studies. An inter-species difference in toxic effects has been found, with dogs particularly susceptible. In this study a method using liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) is described for the analysis of 4-chloro-2-methylphenoxyacetic acid (MCPA), and its metabolite 4-chloro-2-hydroxymethylphenoxyacetic acid (HMCPA), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in human urine. The urine samples were treated by acid hydrolysis to degrade possible conjugations. The sample preparation was performed using solid-phase extraction. Analysis was carried out using selected reaction monitoring (SRM) in the negative ion mode. Quantification of the phenoxyacetic acids was performed using [(2)H(3)]-labeled MCPA and 2,4-D as internal standards. The method was linear in the range 0.05-310 ng/mL urine and has a within-run precision of 2-5%. The between-run precision in lower concentration ranges was between 6-15% and between 2-8% in higher concentration ranges. The limit of detection was determined to 0.05 ng/mL. The metabolites in urine were found to be stable during storage at -20 degrees C. To validate the phenoxyacetic acids as biomarkers of exposure, the method was applied in a human experimental oral exposure to MCPA, 2,4-D and 2,4,5-T. Two healthy volunteers received 200 microg of each phenoxyacetic acid in a single oral dose followed by urine sampling for 72 h post-exposure. After exposure, between 90 and 101% of the dose was recovered in the urine. In the female subject, 23%, and in the male subject 17%, of MCPA was excreted as HMCPA.     

Multivariate Optimization Approach for Chiral Resolution of Chlorophenoxy Acid Herbicides Using Teicoplanin as Chiral Selector in Capillary LC

In this paper, the selectivity and resolution of enantiomeric separation by capillary liquid chromatography (cLC) of racemates of phenoxy acid herbicides are modelled. The compounds studied were 2-(±)-(2,4,5-trichlorophenoxy)propanoic acid (2,4,5-TP), 2-(±)-(2,4-dichlorophenoxy)propanoic acid (2,4-DP), 2-(±)-(4-chloro-2-methyl)phenoxypropanoic acid (MCPP) and 2-(±)-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid] (diclofop acid), using a capillary column packed with silica particles modified with teicoplanin as chiral selector. Several mixtures of methanol (MeOH), water and triethylamine acetate (TEAA) buffer at different pHs have been tested as mobile phases, and experimental parameters such as resolution (Rs), retention factor (k) and enantioselectivity factor (α) have been measured in all tested conditions. The chemometric methods used to explore and to model the data were principal component analysis (PCA), stepwise multiple linear regression (stepwise-MLR) and response surface analysis (RSA). The results show that it is possible to quantitatively predict the quality of enantiomeric separations of related compounds in a given chromatographic system.     

A Fast,Simple Method for Analysis of Phenoxy Acid Salt and Ester Formulations by High Performance Liquid Chromatography

Abstract

Salt formulations of 2,4-D (2,4-dichlorophenoxyacetic acid), 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) and dichlorprop [2-(2,4-dichlorophenoxy)propanoic acid] have been analysed by reversed-phase HPLC using a C18-column with 50:50 (v/v) acetonitrile/2% acetic acid as eluant. Internal and external standard HPLC methods are compared.

Ester formulations of 2,4-D and 2,4,5–T are analysed, without hydrolysis, on the same column using 60:40 (v/v) acetonitrile/2% acetic acid as eluant. The method has been used in this laboratory to determine free phenoxy acid in ester formulations, and for the identification of esters in mixed ester formulations.

The methods are fast and accurate, and offer some advantages over previously-described methods.     

Development and Comparative Study of Different Immunoenzyme Techniques for Pesticides Detection

Abstract

Different ELISA techniques have been developed for the detemination of four widely used pesticides: 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), simazine and atrazine. Dependences between the assay scheme and the limiting detectable concentration of the pesticide were studied. The cases of preferential applying of the scheme with immobilized antibodies or one with immobilized pesticide-protein conjugate have been revealed. The following approaches resulting in lowering of ELISA sensitivity were proposed: preliminary incubation of the tested sample with antibodies, immobilization of antibodies via staphylococcal protein A, usage of monovalent fragments of antibodies instead of native ones and chemical modification of the pesticide molecules in the sample. Optimal combinations of these approaches permitted to lower the detection limit of the assays in about 5–30 times. The achieved sensitivities were 3 ng/mL for 2,4-D, 5 ng/mL for 2,4,5-T, 0.05 ng/mL for simazine, and 0.1 ng/mL for atrazine, being acceptable for purposes of ecological monitoring.