Gas chromatographic behaviour of urea herbicides

Summary Gas chromatographic conditions for determining eight phenylurea (chlortoluron, diuron, fluometuron, isoproturon, linuron, metabenzthiazuron, metobromuron and monuron) and one sulfonylurea (chlorsulfuron) herbicides were assessed. Degradation products of the herbicides formed in the injector were used for identification. Most phenylureas formed their respective carbamic acid methyl esters, metabenzthiazuron formed an aminobenzothiazol and chlorsulfuron formed an aminotriazine plus a phenylsulfonamide. On-column injection of standards using a BP10 capillary column was evaluated to identify the chromatographic behaviour. Detection limits ranged from 0.05 ng for chlorsulfuron to 3 ng for monuron with the NPD and, from 0.01 ng for chlorsulfuron to 5 ng for metabenzthiazuron with the ECD. The RSDs (n=4) were lower than 4% at the 12–25 ng level. The method was applied to the analysis of surface waters extracted with C18 Empore disks with recoveries higher than 85%. Each herbicide could be determined in water down to 0.1 μg·L⁻¹. Chlortoluron was found (11.4 μg·L⁻¹) in a water sample and its presence was confimed by gas chromatography-mass spectrometry.     

Analysis of phenylurea herbicides from plants by GC/MS

Seven phenylurea herbicides (chlorbromuron, fluometuron, diuron, linuron, metobromuron, monolinuron, monuron) were isolated from weed plant materials by extraction with acidic aqueous solutions-the aqueous extract preconcentrated and cleaned-up by using a continuous SPE module. Elution with ethyl acetate resulted in >95% recovery of the herbicides from the LiChrolut-EN sorbent column. Separation of the seven herbicides was easily achieved working under fixed gas-chromatographic conditions and, although other peaks were also detected (corresponding to isocyanate degradation products), they showed different retention times and lower intensity than the parent compounds; in addition, as reproducible chromatograms in terms of herbicide-to-isocyanate product peak areas ratio were obtained, no derivatization was required. The analytical figures of merit of the GC/MS method in the selective ion monitoring mode are as follows: limits of detection from 0.5 to 5.0 ng ml(-1); precision (R.S.D.) approximately 7.0%; and preconcentration factor 100 (using 10 ml of sample extract). The proposed GC/MS method offers better resolution and selectivity than the conventional LC-UV method.     

Multiresidue Analysis of Phenylurea Herbicides in Environmental and Drinking Water by Capillary Electrophoresis

The present paper describes the application of capillary electrophoresis in the micellar mode to the separation and quantitative determination of five phenylurea herbicides, viz. monuron, linuron, diuron, isoproturon, and monolinuron, in water samples. Using uncoated fused silica capillary and phosphate-borate buffer (pH 7.0) containing SDS, the five pesticides are resolved in less than 15 min and quantitatively determined by an ultraviolet detector at 244 nm. Method optimization and validation parameters are presented. Good linearity and repeatability were observed for all the compounds studied (correlation coefficients 0.999). The feasibility of the method developed was tested by simultaneous determination of these herbicides in environmental and drinking water samples at the minimum residue levels (MRLs) (0.1 μg/L) after solid-phase extraction (SPE) preconcentration procedure.     

Effect of ammonium formate as ionizing additive in thermospray liquid chromatography-mass spectrometry for the determination of triazine,phenylurea and chlorinated phenoxyacetic acid herbicides

A comparison between the use of ammonium acetate and ammonium formate in thermospray liquid chromatography-mass spectrometry with positive and negative ion modes using ‘filament-on’ mode has been applied for the determination of simazine, atrazine, propazine, monuron, diuron, linuron, 2,4,-D, 2,4,5-T and silvex. By using ammonium formate, the positive ion mode showed for triazine and phenylurea herbicides [M + H]⁺ and [M + NH₄]⁺, respectively, and the formation of other adduct ions different from ammonium acetate. In the negative ion mode, chlorinated phenoxyacetic acid herbicides exhibited [M + acetate]^? or [M + formate]^?, depending on the ionizing additive. Applications are reported for the determination of triazine and chlorinated phenoxyacetic acid herbicides in spiked soil and water samples, respectively.     

Metal-organic framework-templated synthesis of magnetic nanoporous carbon as an efficient absorbent for enrichment of phenylurea herbicides

Nanoporous carbon with a high specific surface area and unique porous structure represents an attractive material as an adsorbent in analytical chemistry. In this study, a magnetic nanoporous carbon (MNC) was fabricated by direct carbonization of Co-based metal-organic framework in nitrogen atmosphere without using any additional carbon precursors. The MNC was used as an effective magnetic adsorbent for the extraction and enrichment of some phenylurea herbicides (monuron, isoproturon, diuron and buturon) in grape and bitter gourd samples prior to their determination by high performance liquid chromatography with ultraviolet detection. Several important experimental parameters that could influence the extraction efficiency were investigated and optimized. Under the optimum conditions, a good linearity was achieved in the concentration range of 1.0–100.0 ng g⁻¹ for monuron, diuron and buturon and 1.5–100.0 ng g⁻¹ for isoproturon with the correlation coefficients (r) larger than 0.9964. The limits of detection (S/N = 3) of the method were in the range from 0.17 to 0.46 ng g⁻¹. The results indicated that the MNC material was stable and efficient adsorbent for the magnetic solid-phase extraction of phenylurea herbicides and would have a great application potential for the extraction and preconcentration of more organic pollutants from real samples.     

Indirect analysis of urea herbicides from environmental water using solid-phase microextraction

We described here a solid-phase microextraction procedure used to extract six urea pesticides — chlorsulfuron, fluometuron, isoproturon, linuron, metobromuron and monuron — from environmental samples. Two polydimethylsiloxanes and a polyacrylate fiber (PA) are compared. The extraction time, pH control, addition of NaCl to the water and the influence of organic matter such as humic acid on extraction efficiency were examined to achieve a sensitive method. Determination was carried out by gas chromatography with nitrogen–phosphorus detection. The proposed method requires the extraction of 2 ml of sample (pH 4, 14.3%, w/v, NaCl) for 60 min with the PA fiber. The limits of detection range from 0.04 for linuron to 0.1 μg/l for fluometuron and monuron and the relative standard deviations at the 1 μg/l level are between 15% and 9%. The apparent fiber–water distribution constants (K_fw) calculated in the proposed conditions were in the order of 10³. Phenylurea herbicides were indirectly determined in the form of their derived anilines and chlorsulfuron in the form of an aminotriazine as confirmed by gas chromatography–mass spectrometry. Natural waters were utilized to validate the final procedure. However, a unequivocal identification in unknown environmental samples should be done by LC–MS. The presence of dissolved organic matter such as humic acid produces losses during the extraction step. Adding sodium chloride to the sample compensates for this effect.     

Solid-phase microextraction coupled with high-performance liquid chromatography for the determination of phenylurea herbicides in aqueous samples

Solid-phase microextraction coupled with high-performance liquid chromatography was successfully applied to the analysis of nine phenylurea herbicides (metoxuron, monuron, chlorotoluron, isoproturon, monolinuron, metobromuron, buturon, linuron, and chlorbromuron). Polydimethylsiloxane-divinylbenzene (PDMS-DVB, 60 microm) and Carbowax-templated resin (CW-TPR, 50 microm) fibers were selected from four commercial fibers for further study because of their better extraction efficiencies. The parameters of the desorption procedure were studied and optimized. The effects of the properties of analytes and fiber coatings, carryover, duration and temperature of absorption, pH, organic solvent and ionic strength of samples were also investigated. External calibration with an aqueous standard can be used for the analysis of environmental samples (lake water) using either PDMS-DVB or CW-TPR fibers. Good precisions (1.0-5.9%) are achieved for this method, and the detection limits are at the level of 0.5-5.1 ng/ml.     

Determination of linuron and related compounds in soil by microwave-assisted solvent extraction and reversed-phase liquid chromatography with UV detection

The combination of microwave-assisted solvent extraction (MASE) and reversed-phase liquid chromatography (RPLC) with UV detection has been investigated for the efficient determination of phenylurea herbicides in soils involving the single-residue method (SRM) approach (linuron) and the multi-residue method (MRM) approach (monuron, monolinuron, isoproturon, metobromuron, diuron and linuron). Critical parameters of MASE, viz, extraction temperature, water content and extraction solvent were varied in order to optimise recoveries of the analytes while simultaneously minimising co-extraction of soil interferences. The optimised extraction procedure was applied to different types of soil with an organic carbon content of 0.4-16.7%. Besides freshly spiked soil samples, method validation included the analysis of samples with aged residues. A comparative study between the applicability of RPLC-UV without and with the use of column switching for the processing of uncleaned extracts, was carried out. For some of the tested analyte/matrix combinations the one-column approach (LC mode) is feasible. In comparison to LC, coupled-column LC (LC-LC mode) provides high selectivity in single-residue analysis (linuron) and, although less pronounced in multi-residue analysis (all six phenylurea herbicides), the clean-up performance of LC-LC improves both time of analysis and sample throughput. In the MRM approach the developed procedure involving MASE and LC-LC-UV provided acceptable recoveries (range, 80-120%) and RSDs (<12%) at levels of 10 microg/kg (n=9) and 50 microg/kg (n=7), respectively, for most analyte/matrix combinations. Recoveries from aged residue samples spiked at a level of 100 microg/kg (n=7) ranged, depending of the analyte/soil type combination, from 41-113% with RSDs ranging from 1-35%. In the SRM approach the developed LC-LC procedure was applied for the determination of linuron in 28 sandy soil samples collected in a field study. Linuron could be determined in soil with a limit of quantitation of 10 microg/kg.     

液相微萃取／高效液相色谱法测定环境水样中的痕量苯脲类除草剂

建立了液相微萃取／高效液相色谱联用(LPME／HPLC)技术同时测定环境水中痕量异丙隆、秀谷隆和灭草隆除草剂的分析方法.考察了不同萃取条件及测定条件对检测结果的影响.优化后的萃取条件为:6μL正辛醇作萃取剂,液滴体积3μL,搅拌速度450 r/min,萃取30 min.结果表明,在优化条件下,3种除草剂的质量浓度在0....     

Phenylurea herbicides-selective polymer prepared by molecular imprinting using N-(4-isopropylphenyl)-N′-butyleneurea as dummy template

A phenylurea herbicides-selective molecularly imprinted polymer (MIP) was prepared using N-(4-isopropylphenyl)-N′-butyleneurea as a dummy template and toluene as a porogen. The experimental results showed that the optimum molar ratio of template, functional monomer (MAA) and cross-linker (EDMA) was 1:8:20. Scatchard analysis showed that two classes of binding sites were formed in the imprinted polymer with dissociation constants of 26.81 μmol l⁻¹ and 1.428 mmol l⁻¹. The affinity and selectivity of MIP for phenylurea herbicides were studied. Among the 14 phenylurea herbicides tested, the MIP prepared showed obviously high affinity and selectivity for 10 chemicals (monuron, diuron, isoproturon, fenuron, chlortoluron, difenoxuron, metoxuron, neburon, buturon and fluometuron) with dichloromethane containing 10% hexane as mobile phase while non-imprinted polymer showed very low affinity for all the phenylurea herbicides tested. The experimental and calculated results also indicated that the size and property of the group at the N′ position of phenylurea molecules have great influence on the affinity of MIP for them and the recognition site is mainly located at the N′ position of phenylurea herbicides.     

Development of a rapid, specific fluorescence polarization immunoassay for the herbicide chlorsulfuron

A strategy for design of a derivative of chlorsulfuron, which mimics half of the herbicide molecule, was proposed. The 1-[(2-chloro)phenylsulfonyl]monoamidosuccinic acid was synthesized as a derivative of chlorsulfuron for conjugation to carrier proteins. Rabbits were immunized and the resulting polyclonal antibodies were assessed by the fluorescence polarization technique. The antibodies were highly specific to chlorsulfuron. Cross-reactivity to the structurally similar sulfonylurea and urea herbicides chlorbromuron, amidosulfuron, chlortoluron, isoproturon, diuron and linuron was less than 0.1%. A rapid fluorescence polarization immunoassay (FPIA) for chlorsulfuron detection in water samples was developed and optimized. The detection limit of chlorsulfuron in 50 μl of sample was 10 ng ml⁻¹. Total time for the measurement of 10 samples is 7 min. The proposed FPIA is suitable for rapid testing for pesticide contamination where the highest sensitivity is not critical or in combination with pre-concentration techniques.     

Clean up of phenylurea herbicides in plant sample extracts using molecularly imprinted polymers

Two different molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using linuron or isoproturon (phenylurea herbicides) as templates and trifluormethacrylic acid as functional monomer. These materials were used as selective sorbents in the development of molecularly imprinted solid-phase extraction (MISPE) procedures for the determination of several phenylurea herbicides (fenuron, metoxuron, chlortoluron, isoproturon, metobromuron, and linuron) in plant samples extracts. The MISPE procedures were fully optimized and applied to the clean up of selected phenylurea herbicides in carrot, potato, corn, and pea sample extracts and finally determined by HPLC-UV at 244 nm. Although a high degree of clean up was obtained, a decrease of the MIP recognition capabilities was observed in subsequent runs. Thus, a previous clean up protocol based on the use of a non-imprinted polymer was used to prevent the loss of MIP performance and to ease the removal of interferences. Following this procedure, namely two-step MISPE, matrix compounds were almost completely removed by the non-imprinted polymer retaining the ability of MIPs to selectively rebind target analytes unaltered. The developed MISPE procedures allowed the screening of phenylurea herbicides in plant samples at concentration levels required by established European maximum residue limits.     

苯基脲类除草剂分子印迹聚合物的合成和识别性能研究

以N-(4-异丙基苯基)-N′-亚丁基脲为模板, 甲基丙烯酸为功能单体, 乙二醇二甲基丙烯酸酯为交联剂制备了分子印迹聚合物(MIP). 研究了MIP对苯基脲类除草剂的亲和性和选择性. 在二氯甲烷流动相中制备的MIP对异丙隆(IP)、 非草隆(FN)、 甲氧隆(MX)、 敌草隆(DU)、 绿麦隆(CT)、 枯莠隆(DF)、 灭草隆(MN)、 草不隆(NB)、 播土隆(BT)和伏草隆(FU)等除草剂呈现出较高的亲和性, 而非印迹聚合物(NIP)对文中所用的14种苯基脲类除草剂均表现出非常低的保留或几乎没有保留. 实验及Mulliken电荷计算的结果显示， 苯基脲除草剂分子中的N′原子是主要的识别位点.     

Polar herbicides,pharmaceutical products,perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA), and nonylphenol and its carboxylates and ethoxylates in surface and tap waters around Lake Maggiore in Northern Italy

A survey of contamination of surface and drinking waters around Lake Maggiore in Northern Italy with polar anthropogenic environmental pollutants has been conducted. The target analytes were polar herbicides, pharmaceuticals (including antibiotics), steroid estrogens, perfluorooctanesulfonate (PFOS), perfluoroalkyl carboxylates (including perfluorooctanoate PFOA), nonylphenol and its carboxylates and ethoxylates (NPEO surfactants), and triclosan, a bactericide used in personal-care products. Analysis of water samples was performed by solid-phase extraction (SPE) then liquid chromatography–triple-quadrupole (tandem) mass spectrometry (LC–MS–MS). By extraction of 1-L water samples and concentration of the extract to 100 μL, method detection limits (MDLs) as low as 0.05–0.1 ng L⁻¹ were achieved for most compounds. Lake-water samples from seven different locations in the Southern part of Lake Maggiore and eleven samples from different tributary rivers and creeks were investigated. Rain water was also analyzed to investigate atmospheric input of the contaminants. Compounds regularly detected at very low concentrations in the lake water included: caffeine (max. concentration 124 ng L⁻¹), the herbicides terbutylazine (7 ng L⁻¹), atrazine (5 ng L⁻¹), simazine (16 ng L⁻¹), diuron (11 ng L⁻¹), and atrazine-desethyl (11 ng L⁻¹), the pharmaceuticals carbamazepine (9 ng L⁻¹), sulfamethoxazole (10 ng L⁻¹), gemfibrozil (1.7 ng L⁻¹), and benzafibrate (1.2 ng L⁻¹), the surfactant metabolite nonylphenol (15 ng L⁻¹), its carboxylates (NPE₁C 120 ng L⁻¹, NPE₂C 7 ng L⁻¹, NPE₃C 15 ng L⁻¹) and ethoxylates (NPE _n Os, n = 3-17; 300 ng L⁻¹), perfluorinated surfactants (PFOS 9 ng L⁻¹, PFOA 3 ng L⁻¹), and estrone (0.4 ng L⁻¹). Levels of these compounds in drinking water produced from Lake Maggiore were almost identical with those found in the lake itself, revealing the poor performance of sand filtration and chlorination applied by the local waterworks.     

Use of on-line liquid chromatography-nuclear magnetic resonance spectroscopy for the rapid investigation of flavonoids from Sorocea bomplandii

A HPLC method, using photochemically-induced fluorescence detection, is described for the separation and determination of four phenylurea herbicides including diuron, isoproturon, linuron and neburon. A post-column photoreactor, consisting of a reactor knitted around a 4 W xenon lamp, has been included between the column and the detector, in order to transform the non-fluorescent herbicides into fluorophors. The influence of mobile phase composition, flow-rate, pH, and buffer concentration has been studied. An acetonitrile–buffer solution of potassium phosphate dibasic of pH 7 and 0.01 M concentration (60:40, v/v), was selected as optimum. For the fluorimetric detection, optimal excitation/emission wavelengths 324/403, 301/433, 335/411 and 326/385 nm were selected for the determination of diuron, isoproturon, linuron and neburon, respectively. The detection limits ranged between 0.07 and 0.46 μg/ml, according to the compound.     

Preparation of antibodies and development of a sensitive immunoassay with fluorescence detection for triazine herbicides

Specific polyclonal antibodies against s-triazine herbicides were obtained by preparing immunogens coupling home-synthesized haptens derivatives of simazine (6-chloro-N-ethyl-N′-ethyl-1,3,5-triazine-2,4-diamine) to lysine groups of hemocyanin from keyhole limpets and bovine serum albumin carrier proteins. Three highly sensitive rabbit antisera were obtained and evaluated with a battery of six enzyme tracers derived from triazine structures in an optimized ELISA format. The antiserum As8 and the HRP-2f tracer, which yield the best assay sensitivity for simazine (detection limit 0.11 ± 0.02 μg L⁻¹, IC₅₀ 0.88 ± 0.04 μg L⁻¹), were applied to the development of a sensitive flow-through immunoassay for the analysis of this herbicide. The automated assay was based on a direct competitive immunosorbent assay and fluorescence detection. The optimized method presents an IC₅₀ value of 0.35 ± 0.04 μg L⁻¹ with a detection limit of 1.3 ± 0.9 ng L⁻¹ and a dynamic range from 0.010 to 7.5 μg L⁻¹ simazine. The generic nature of the antiserum was shown by good relative cross-reactivities with other triazines such as atrazine (420%) or propazine (130%) and a lower response to terbutylazine (6.4%) and desethyl-atrazine (2.2%). No cross-reactivity was obtained for nonrelated pesticides such as 2,4-dichlorophenoxyacetic acid or linuron and the assay could be applied as a screening method for triazine herbicides. The total analysis time was 30 min per determination and the immunosensor could be reused for more than 150 cycles without significant loss of activity. The immunosensor has been successfully applied to the direct analysis of simazine in surface water samples at the nanogram per liter level. The results obtained by comparative analysis of the immunosensor with a chromatographic procedure for triazines showed a close correspondence.     

High-performance liquid chromatography column switching applied to the trace determination of herbicides in environmental and drinking water samples

A selective and sensitive coupled-column high-performance liquid chromatographic method is developed for the simultaneous determination of 5 phenylurea herbicides (monuron, linuron, isoproturon, monolinuron, and diuron) in environmental and drinking water samples. Sample clean-up is performed automatically by means of a column switching technique. Using 2 octadecyl silica columns connected via two programmable 6-port valves and ultraviolet detection at 244 nm, the aforementioned compounds can be determined at the low concentration levels required for pesticide residue analysis in water samples. A mobile phase consisting of a mixture of methanol-water (55:45, v/v) is pumped at 1 mL/min. For the 5 phenylureas, high recoveries ranging from 94.9 to 101.6%, good reproducibility with relative standard deviations lower than 5%, and wide linear ranges up to 20 micrograms/L are observed with determination limits of 0.05 microgram/L. The method is successfully applied to the screening of different environmental water samples such as surface, ground, rain, and drinking water.     

Analysis of phenylurea and propanil herbicides by solid-phase microextraction and liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection

This study examines the application of solid-phase microextraction coupled with high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME-HPLC-PIF-FD) for the determination of four phenylurea herbicides (monolinuron, diuron, linuron and neburon) and propanil in groundwater. Direct immersion (DI) SPME was applied using a 60 μm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber for the extraction of the pesticides from groundwater samples. An AQUASIL C₁₈ column (150 mm × 4.6 mm i.d., 5 μm) was used for separation and determination in HPLC. The method was evaluated with respect to the limits of detection (LODs) and the limits of quantification (LOQs) according to IUPAC. The limits of detection varied between 0.019 μg L⁻¹ and 0.034 μg L⁻¹. Limits of quantification ranged between 0.051 μg L⁻¹ and 0.088 μg L⁻¹. These values meet the recommended limits for individual pesticides in groundwater (0.1 μg L⁻¹) established by the EU. Recoveries ranged between 86% and 105% and relative standard deviation values between 2% and 8%.     

Determination of phenylureas herbicides in food stuffs based on matrix solid-phase dispersion extraction and capillary electrophoresis with electrochemiluminescence detection

A new method based on matrix solid phase dispersion-capillary electrophoresis with electrochemiluminescence detection (MSPD-CE-ECL) has been developed for the simultaneous determination of three kinds of phenylurea herbicides (PHUs). Poly-β-cyclodextrin (poly-β-CD) was used as an additive in the running buffer to improve the separation of three analytes. The conditions for CE separation, ECL detection and effect of poly-β-CD were investigated in detail. Under the optimal conditions, three kinds of herbicides (isoproturon, linuron and diuron) were well separated and detected within 8 min. The linear ranges of the standard solution for isoproturon and linuron were 1-300 μg L(-1) with a detection limit (S/N=3) of 0.1 μg L(-1), and for diuron was 2-500 μg L(-1) with a detection limit of 0.2 μg L(-1). The average recoveries were in the range of 86.9-102.8%, and all relative standard deviation of the migration time and the ECL intensity in intraday and interday were less than 9.0%. The proposed method was also applied to the determination of three kinds of herbicides in green vegetable and rice samples with recoveries in the range from 78.1 to 93.8%.     

Evaluation of a mixed immunosorbent for selective trace enrichment of phenylurea herbicides from plant material

A mixed immunosorbent, composed of anti-isoproturon and anti-chlortoluron antibodies immobilized on aldehyde-activated silica was evaluated for the trace enrichment and clean-up of several phenylurea herbicides from potatoes, carrots and peas. As the immunosorbent exhibited non-specific interactions with the matrix components, a previous clean-up step based on gel filtration (Sephadex G-25 PD-10 column) or anion-exchange (Power 1 × 8 Dionex column) was necessary. The coupling of gel filtration and immunosorbent with subsequent HPLC/UV determination allowed the determination of selected herbicides in potatoes in the 30 ng/g range with high precision, but for more complex samples (carrots and peas) the combination of anion-exchange resin and immunosorbent was required. With 30 ng/g spiked samples recovery rates for isoproturon, chlortoluron, metobromuron, linuron and chlorbromuron averaged 80 ± 20% (n = 5 in two consecutive days) for the whole procedure and the estimated detection limits ranged from 5 to 20 ng/g. Received: 29 January 1998 / Revised: 4 May 1998 / Accepted: 30 May 1998