Atrazine and simazine determination in river water samples by micellar electrokinetic capillary chromatography

Determination of imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by application of micellar electrokinetic capillary chromatography with solid-phase extraction

A method is described for the analysis of the insecticide imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] and its metabolite 6-chloronicotinic acid by micellar electrokinetic chromatography with diode-array detection at 270 and 227 nm, respectively. The best results were obtained using sodium dodecyl sulphate at a concentration of 60 mM and a running buffer of NH4Cl/NH3 at 15 mM (pH 8.5). The selection of instrumental parameters such as voltage at 30 kV with an injection time of 20 s gave the best resolution with an analysis time of less than 6 min. The method yields similar sensitivity for the parent compound and for the metabolite, with detection limits of 0.71 and 1.18 microg/ml for imidacloprid and 6-chloronicotinic acid, respectively. The sampling and analysis of these two pesticides in greenhouse air was carried out using personal samplers connected to XAD-2 cartridges as sampling media, investigating the dissipation of analytes in a 24-h period after their application.

Analysis of glycopeptide antibiotics using micellar electrokinetic chromatography and borate complexation

Micellar electrokinetic chromatography (MEKC) was investigated as a technique for the separation and analysis of the following related glycopeptide antibiotics: alpha-avoparcin, beta-avoparcin, ristocetin A, ristocetin B and vancomycin. Sodium dodecyl sulfate (SDS) micelles were employed as the pseudostationary phase in conjunction with borate or CHES buffers at pH 9.2. A complete separation of the glycopeptides was achieved only when two separation mechanisms were employed simultaneously: (i) differential partitioning of the glycopeptides into SDS micelles; and (ii) differential complexation of the glycopeptides with the borate anion from the borate buffer. Quantitatively, linearity was confirmed for each antibiotic from 0.5 to 40 ppm, with correlation coefficients (r(2)) ranging from 0.9996 (vancomycin and beta-avoparcin) to 0.9986 (alpha-avoparcin). Detection limits ranging from 0.01 ppm (vancomycin) to 0.2 ppm (avoparcin) were achieved, and the mean recovery of avoparcin at the 10 ppm level was 99.2%.

On-line concentration of s-triazine herbicides in micellar electrokinetic chromatography using a cationic surfactant

On-line concentration of neutral species of s-triazine herbicides in micellar electrokinetic chromatography using tetradecylammonium bromide (TTAB) as a cationic surfactant was investigated. Factors affecting the stacking of analytes were examined. The results indicate that the stacking efficiency is markedly improved with addition of phosphate buffer in the sample matrix. It was found that, depending on the nature of the analytes, the most effective stacking of these analytes occurs when the ratio of the conductivity of buffer electrolyte to that of sample matrix is in the range 1.4-1.2, with sample matrix containing phosphate buffer. Micelle concentration in the separation buffer is also a crucial factor to enhance the stacking efficiency and detection sensitivity of analytes. Moreover, the stacking efficiency of each individual analyte depends on its binding constant to TTAB micelles. The concentration effect is primarily based on sweeping mechanism which is operated in a normal stacking mode with reversed electrode polarity in the presence of reversed electroosmotic flow. As a result of concentration enhancement, the detection limits of these herbicides can reach about 9-15 ng/ml with UV detection.

Investigation of atrazine metabolism in river sediment by high-performance liquid chromatography/mass spectrometry

Microbial degradation processes play an important role in chemical water clearance taking place in river sediments. Bacteria remove not only easily degradable organic species, but various xenobiotics as well, producing clear and xenobiotic free water for bank-filtered wells. Atrazine is a widely used herbicide, and it is one of the most common xenobiotics present in Danube water. In this study the pathway and kinetics of atrazine metabolism of sedimental microbiota were studied. Samples were collected from river sediment and from pure microbial growth cultures. An analytical scheme including sample preparation, chromatography and mass spectrometry was developed and optimised. Solid-phase extraction (SPE) was found to be satisfactory for sample preparation. For qualitative analysis of samples both reversed-phase and normal-phase high-performance liquid chromatography/mass spectrometry (HPLC/MS) methods were developed and used. Selectivity, detection limits and accuracy of the two methods were compared. Using this analytical scheme, the full atrazine metabolism of the organism Comamonas acidovorans was explored. Altogether, 12 metabolites were identified from the original compound to the urea end product. Detection limits in the range of 50 ng L(-1)-1 microg L(-1) were obtained for different metabolites.

Herbicide and plant growth regulator analysis by capillary electrophoresis

Capillary electrophoresis (CE) is a relatively new analytical technique that is just beginning to be employed in the area of pesticide residue analysis. With the development of more sensitive detectors and in conjunction with CE separation powers, it should be a well accepted technique for pesticide residue analysis in the future. This review describes CE methods that have been developed to analyze herbicides and grow regulators in water, soil and food.

Capillary zone electrophoretic separation of neutral species of chloro-s-triazines in the presence of cationic surfactant monomers

Chloro-s-triazines are difficult to separate by capillary zone electrophoresis (CZE), due to their low pKa values. However, these analytes can be effectively separated by CZE in the presence of cationic surfactant monomers, such as tetradecylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB). The separation mechanism based on a 1:1 binding of analytes to cationic surfactant monomers is proposed. The binding constants of chloro-s-triazines to cationic surfactant monomers are estimated. The results show that the strength of the interactions of these analytes with TTAB monomers is considerably strong, whereas that of the corresponding analyte with DTAB monomers is about 12- to 14-fold weaker. A linear correlation of binding constants with log P(ow) (the logarithm of the partition coefficient of analytes between 1-octanol and aqueous phases) indicates that the migration order of these chloro-s-triazines depends primarily on their hydrophobicity. Moreover, the skewed peaks of chloro-s-triazines observed may reveal the occurrence of adsolubilization of these analytes in the adsorbed cationic surfactant layer on the capillary surface.

Trace-level determination of triazines and several degradation products in environmental waters by disk solid-phase extraction and micellar electrokinetic chromatography

An analytical method combining disk solid-phase extraction with micellar electrokinetic chromatography has been developed for the determination of atrazine, simazine, hydroxyatrazine, deisopropylatrazine, deethylatrazine, propazine and prometryn in water samples. The influence of the buffer and sodium dodecyl sulfate (SDS) concentration, pH and organic modifier on the separation has been studied. Baseline separation of the seven triazines was achieved under the following conditions: 10 mM borate buffer, 60 mM SDS, 20% methanol and pH 9.2. C18-bonded silica and poly(styrene-divinylbenzene) (PS-DVB) disks were evaluated for solid-phase extraction of the selected pesticides (11 of water sample). Using two PS-DVB disks, quantitative recoveries were obtained for all pesticides tested. The method was successfully applied for the determination of the seven triazines in drinking and well water at the 0.1 microg l(-1) and 0.5 microg l(-1) concentration levels, respectively. The detection limits for these analytes using the proposed analytical method were within the 0.02-0.06 microg l(-1) range in drinking water and the 0.06-0.30 microg l(-1) range in well water.

Determination of triazine herbicides in natural waters by solid-phase extraction and non-aqueous capillary zone electrophoresis

Capillary zone electrophoresis (CZE) in an organic medium was used to analyse triazines at sub-ppb concentration levels in natural waters after a preconcentration step using conventional C18 cartridges and new Oasis HLB devices. With both sorbents, satisfactory results were obtained on analysing deionized water. However, on analysing natural waters, both sorbents showed very different types of behaviour. The different variables affecting the elution of both sorbents were studied, resulting in the choice of Oasis HLB as the most suitable for later separation by CZE in non-aqueous medium. Combination of a preconcentration step with electrokinetic injection revealed that capillary electrophoresis with simple UV detection can also be used satisfactorily for the quantification of micropollutants in natural waters. The detection limits obtained varied between 0.01 and 0.05 microg l(-1), depending on the type of matrix analysed. The day-to-day precision varied between 0.9% and 2.3%, expressed as the relative standard deviation.

Analysis of atrazine, terbutylazine and their N-dealkylated chloro and hydroxy metabolites by solid-phase extraction and gas chromatography-mass spectrometry and capillary electrophoresis-ultraviolet detection

Solid-phase extraction (SPE) with the styrene-divinylbenzene adsorbent LiChrolut EN was investigated for the extraction of the s-triazine herbicides atrazine and terbutylazine, their polar N-dealkylated degradation products deethylatrazine (DEA), deisopropylatrazine (DIA) and deethylterbutylazine (DET) and for the hydrophilic hydroxytriazine degradation products (HTDPs) hydroxyatrazine (HA), hydroxyterbutylazine (HT), deethylhydroxyatrazine (DEHA), deisopropylhydroxyatrazine (DIHA) and deethyldeisopropylhydroxyatrazine (ameline). The optimum pH value for the extraction of the HTDPs from fortified tap water at 2 micrograms/l is 3.0. Recovery values with 200 mg LiChrolut EN are > 80% for HA, HT, DEHA and 30% for DIHA from 200 ml spiked tap and river water. Atrazine, terbutylazine, DEA, DIA and DET are quantitatively extracted by LiChrolut EN. The chlorotriazines are analyzed by GC-MS and the HTDPs by capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC) with an acetate buffer at pH 4.6 or a sodium borate-sodium dodecyl sulfate buffer at pH 9.3. The combined method of SPE enrichment and CE analysis allows the determination of HTDPs in the low microgram/l range.

Determination of hexazinone and its metabolites in groundwater by capillary electrophoresis

A micellar electrokinetic chromatographic method was developed to separate and quantify hexazinone and metabolites C, A1, E, B and D in groundwater. Hexazinone and its metabolites were extracted from water using Supelclean ENVI-Carb solid-phase extraction tubes. Quantitation was performed using UV photodiode detection at 220, 225, 230 and 247 nm. Intra-assay and inter-assay reproducibility studies run at 0.5, 1.0, 2.0 and 5.0 ppb indicated the procedure was reproducible. Groundwater samples collected from US Geological Survey monitoring wells were analyzed for hexazinone and its metabolites by CE. A comparison was made between CE and an established HPLC method of the hexazinone and metabolite B. The linear regression for hexazinone was y = 1.007x + 0.219 with a correlation coefficient of 0.96 while the linear regression for metabolite B was y = 1.100x-0.057 with a correlation coefficient of 0.91.

Capillary electrophoresis of pesticides

Pesticides are important and diverse environmental and agricultural species. Their determination in pesticide formulations, in feed and food, and in complex environmental matrices (e.g., water, soil, sludge, sediments, etc.) often requires separation methods of high efficiency, unique selectivity and high sensitivity. As shown in this comprehensive review, capillary electrophoresis meets these requirements and has proved to be a suitable microseparation technique for the analysis of a wide variety of chiral and achiral pesticides. It is also shown that by combining selective precolumn derivatization schemes, sensitive detection methods (e.g., laser induced fluorescence detection) and trace enrichment techniques, capillary electrophoresis (CE) is capable of determining pesticides at trace levels as those usually encountered in environmental samples.

Combination of solid-phase extraction and field-amplified concentration for trace analysis of organonitrogen pesticides by micellar electrokinetic chromatography

An analytical method based on the combination of solid-phase extraction (SPE) and field-amplified concentration (FAC), with micellar electrokinetic chromatography (MEKC) was developed to extract, concentrate, separate, and quantitate six organonitrogen pesticides (metribuzin, bromacil, terbacil, hexazinone, triadimefon, and DEET) in drainage water. The recovery of the first five pesticides was over 85%, and the limit of detection was 0.8 ppb. Four advantages (enhanced enrichment and recoveries, reduced extraction time and interferences) of combining SPE with FAC for trace analysis of pesticides at the ppb level were demonstrated.

Micelles as pseudo-stationary phases in micellar electrokinetic chromatography

This review article describes some general comments on micellar electrokinetic chromatography (MEKC) from the viewpoint of pseudo-stationary phases and presents a compiled list of surfactants used for MEKC, prepared from published papers. We tried to give comments on some typical surfactants from the practical point of view.

Stereoselective analysis of herbicides by capillary electrophoresis using sulfobutyl ether beta-cyclodextrin as chiral selector

Capillary zone electrophoresis has been used for the enantiomeric separation of several herbicides. Different beta-cyclodextrin (CD) derivatives have been investigated for chiral separations and among them the negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) proved to be effective for the stereo-selective resolutions of the investigated herbicides. The effect of CD concentration, buffer pH and organic modifier on effective mobilities, resolution and selectivity of the analytes have been studied. Addition of SBE-beta-CD (5-50 mg/mL) to the buffer at pH 9 resulted in a general increase of migration times as well as resolution. A CD concentration as low as 5 mg/mL was effective to completely resolve napropamide and ethofumesate enantiomers. Buffer solutions containing 40 mg/mL of SBE-beta-CD were chosen to study the effect of buffer pH (7, 8, and 9) on chiral separation of the herbicides. No great differences in resolution and effective mobilities have been found in the pH 7-9 range. The addition of different organic modifiers to the background electrolyte at pH 9, containing 20 mg/mL of SBE-beta-CD, showed different effects. Methanol was the most effective in improving resolution but in some cases total loss in enantiomeric separation was observed. The qualitative analysis of an enantiomerically pure herbicide (flamprop isopropyl) commercial preparation is also shown.

Separation of fungicides by micellar electrokinetic capillary chromatography

Capillary electrophoresis with ultraviolet detection (CE/UV) of selected fungicides (carbendazim, metalaxyl, propiconazole, and vinclozolin) using different buffer compositions was investigated. Capillary zone electrophoresis (CZE) with 10 mM sodium phosphate (pH 7.0) was not useful in separating the four fungicides used in this study. However, the four fungicides were well resolved by employing micellar electrokinetic capillary chromatography (MEKC). Among the two surfactants tested in MEKC, bile salts provided better separation compared to sodium dodecyl sulfate (SDS). A buffer consisting of 10 mM sodium phosphate with 100 mM sodium cholate and 10% methanol (pH 7.0) gave best results; excellent separation of the four compounds was achieved in less than 15 min. The CE/UV method was validated by analyzing deionized and lake-water samples fortified with known concentrations for the four fungicides. Average recoveries of the fungicides in lake water of 4 micrograms/L level ranged from 42 to 87%.

Monitoring of herbicide pollution in water by capillary electrophoresis

In recent years, capillary electrophoresis (CE) has demonstrated itself to be an extremely powerful analytical technique. However, CE has not yet been fully evaluated for the environmental analysis of herbicides. In this paper, the potential and drawbacks of CE for the separation and detection of herbicides in water sources are outlined. Details are given both on the applicability of CE to trace level monitoring of herbicides in water sources and on its usefulness in studies regarding the environmental behaviour of herbicides in water systems.