Highly efficient microextraction of chlorophenoxy acid herbicides in natural waters using a decanoic acid-based nanostructured solvent prior to their quantitation by liquid chromatography–mass spectrometry

Solvents used in microextraction require high solubilising capability to efficiently extract the target compounds. In this article, nanostructured solvents made up of alkyl carboxylic acids (ACAs) aggregate are proposed for the efficient microextraction of acidic pesticides from natural waters. The target compounds were chlorophenoxy acid herbicides (CPAHs) widely used in agriculture, forestry and gardening (viz. 2,4-D, MCPA, MCPP, 2,4,5-T and MCPB). The supramolecular solvents (SUPRASs) tested were generated from solutions of reverse micelles of octanoic (OcA), decanoic (DeA) and dodecanoic (DoA) acid in THF by the addition of water, which acted as the coacervating agent. The DeA-based SUPRAS was the most efficient extractant for CPAHs; actual concentration factors (ACFs) of 260 for 2,4-D, 290 for MCPA, and 400 for MCPP, 2,4,5-T and MCPB were obtained. The explanation for so high ACFs can be found in the extremely efficient retention mechanisms that the DeA-based SUPRAS provides for CPAHs (i.e. formation of hydrogen bonds and hydrophobic interactions), and the high number of binding sites that it contains (i.e. the concentration of biosurfactant in the SUPRAS was 0.56 mg μL⁻¹). Both characteristics permitted to effectively extract the target analytes in a low volume of solvent (about 2 μL of solvent per mL of sample). Others assets of the proposed supramolecular solvent-based microextraction (SUSME) approach included recoveries no dependent on matrix composition, rapidity (sample treatment spent about 15 min), use of low volume of sample (63 mL per analysis) and simplicity (no special lab equipments was needed). Combination with liquid chromatography/ion–trap mass spectrometry [LC–(IT)MS] afforded method quantitation limits for CPAHs within the interval 22–30 ng L⁻¹. The precision of the method, expressed as relative standard deviation (n = 11, [CPAH] = 200 ng L⁻¹), was in the range 2.9–5.8%. The applicability of the method to the analysis of natural waters was assessed by determining the target analytes in fortified river and underground water samples.     

Determination of Some Bipyridylium Herbicides by Ring-Oven Techniques

Abstract

The development of a rapid and a simple “Weisz ring-oven” method is described for the semiquantative determination of diquat and paraquat. In this method column chromatography is used for the separation of herbicides from water and soil samples. Further evidence of the identity of individual residues is provided by thin layer chromatography.     

Sensitive and Selective Fluorescence Detection of Phenoxyacid Herbicides by Liquid Chromatography with On-Line Ion-Pair Extraction

Abstract

Fluorescent probes, especially a newly synthesized N-substituted 1-cyanobenz[f]-isoindole quaternary ammonium fluorophore, were used as counter ions in a reaction detector for on-line ion-pair extraction of phenoxyacid herbicides. The probe was used in an on-line post-column set-up coupled to a reversed-phase chromatographic system. After separation on an C-8-bonded silica column using an aqueous methanol (pH 2.5) mobile phase, the herbicides were on-line deprotonated by post-column addition of a 10mM sodium phosphate buffer (pH 8.0), in which the probe was dissolved. Subsequently, the ion-pairs were extracted on-line with chloroform-1-butanol (80:20, v/v) and were monitored by fluorescence detection. Using this system, at least seven herbicides could be separated. The detection limits of 2,4-dichlorophe xyacetic acid and 2,4,5-trichlorophenoxyacetic acid were 400 pg (S/N = 3). The repeatability, based on peak height measurements, for 100ng injections was about 0.5%. Calibration curves were linear over the investigated range of 1–100ng, with correlation coefficients of 0.999 for the two analytes. Application to a drinking water sample is presented.     

4‐Hydroxyphenylpyruvate Dioxygenase Inhibitors in Combination with Safeners: Solutions for Modern and Sustainable Agriculture

Inhibitors of 4‐hydroxyphenylpyruvate dioxygenase (HPPD) prevent plant carotenoid pigment formation, which in turn leads to chlorophyll degradation. This “bleaching” herbicide mode of action provides weed‐control products for various crops, such as rice, corn, and cereals. Combinations with suitable safeners allow the full exploitation of the potential of this compound class to selectively control major weed problems, including rapidly increasing cases of resistance against other important herbicide classes.     

Analysis of Phenoxycarboxylic Acids and Other Acidic Compounds in Tap,Ground, Surface and Sewage Water at the Low ng/1 Level

Abstract

Solid-phase extraction with RP-C18 phase has been successfully applied for the determination of more than 30 acidic herbicides and related compounds from environmental water samples. Detection of these contaminants was performed after pentafluorobenzylation at the low ng per liter level using gas chromatography/mass spectrometry. With multiple-component SIM programming simultaneous detection of all compounds in one single gas chromatographic run was possible.

Increased reliability of acidic herbicide analysis from water samples with high matrix content was achieved by using a surrogate as well as an internal standard. 2-(4-chlorophenoxy) butyric acid, being a structural isomer of clofibric acid and mecoprop, was chosen as surrogate standard because cloflbric acid was found to be a widespread contaminant in environmental water samples from the Berlin area. Mecoprop, dichlorprop and 1-naphthylacetic acid were also found in field studies of some of these samples. A few examples of positive findings in tap, ground, surface and sewage water samples are presented.     

Dispersive liquid–liquid microextraction combined with high performance liquid chromatography-DAD detection for the determination of sulfonylurea herbicides in water samples

A new method for the determination of four sulfonylurea herbicides (metsulfuron-methyl, chlorsulfuron, bensulfuron-methyl and chlorimuron-ethyl) in water samples was developed by dispersive liquid–liquid microextraction coupled with high performance liquid chromatography-diode array detector. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction and disperser solvent, extraction time and salt addition, were investigated and optimised. Under the optimum conditions, the enrichment factors were in the range between 102 and 216. The linearity of the method was obtained in the range of 1.0–100 ng mL^?1 with the correlation coefficients (r) ranging from 0.9982 to 0.9995. The method detection limits were 0.2–0.3 ng mL^?1. The proposed method has been successfully applied to the analysis of target sulfonylurea herbicides in river, stream and well water samples with satisfactory results.     

In-Block Derivatization of Herbicidal Carboxylic Acids by Pentafluorobenzyl Bromide

Abstract

Herbicidal carboxylic acids were analyzed via ECD gas chromatography of their pentafluorobenzyl esters. The derivatives were formed by direct injection of a mixture of the acids and pentafluorobenzyl bromide in acetone; yields showed marked dependence on pKa of the acids. Carboxylic acids which have pKa values greater than 4.5 yielded the corresponding derivatives in poor yield unless triethylamine is included in the mixture. The procedure is fast and particularly convenient for low-level screening, identification and analysis of highly acidic chlorobenzoic, chlorophenoxyalkanoic, and arylacetic acids in the presence of less acidic carboxylic acids and phenols.     

New immunosensors for 2,4-D and 2,4,5-T pesticides determination

New immunosensors for 2-(2, 4-dichlorophenoxy) acetic acid (i.e. 2,4-D) and (2, 4, 5-trichlorophenoxy) acetic acid (i.e. 2,4,5-T) pesticide determination were developed using a non commercial antibody, hydrogen peroxide transducer and horseradish peroxidase as enzyme marker. The results show the full validity of these immunosensor devices, which were optimized using a ‘competition’ separation procedure. These immunosensors were also used to test pesticide recovery in common real matrices such as field grass, maize and wheat samples, for which good results were obtained. The immunosensors developed demonstrated a good selectivity versus different kinds of pesticides and may thus be considered as suitable devices for application to real matrices (LOD?=?8.0?×?10^?11?mol?L^?1; RSD%?=?5.2 for 2,4-D and LOD?=?2.8?×?10^?9?mol?L^?1; RSD%?=?6.1 for 2,4,5-T).     

络合萃取-在线衍生土壤酸性除草剂条件选择与优化

以Na4EDTA为络合剂,以五氟苄基溴为衍生试剂,采用快速溶剂萃取仪萃取,同时实现土壤酸性除草剂的络合萃取在线衍生,并以气相色谱-质谱(NCI源)进行检测。对络合条件、衍生条件、萃取条件、离子源选择进行了优化。方法的回收率为75%～95%、相对标准偏差为6.7%～13%、检测限2.8～8.4μg/Kg。     

Gas‐phase Smiles Rearrangement of Sulfonylurea Herbicides in Electrospray Ionization Mass Spectrometry

In the negative ion mode of electrospray ionization tandem mass spectrometry (ESI‐MS/MS) of four sulfonylurea herbicides, Smiles rearrangements were observed in rimsulfuron and nicosulfuron. In the case of rimsulfuron, two competitive gas‐phase Smiles rearrangements initiated by nitrogen anion and oxygen anion respectively were witnessed. The ion‐neutral complex was proposed as the reactive intermediate in the course of this unimolecular dissociation reaction of the oxygen attack Smiles rearrangement route. The density functional theory (DFT) was carried out to elucidate the mechanism as well as to show the possible transition states and the intermediates.