Simultaneous quantification of acetanilide herbicides and their oxanilic and sulfonic acid metabolites in natural waters

Determination of alachlor, metolachlor, and their acidic metabolites in soils by microwave-assisted extraction (MAE) combined with solid phase extraction (SPE) coupled with GC-MS and HPLC-UV analysis

A well-validated analytical method based on microwave-assisted extraction (MAE) and SPE is presented for the combined analysis of alachlor, alachlor-oxanilic acid (OXA), alachlor-ethanesulfonic acid (ESA), metolachlor, metolachlor-OXA, metolachlor-ESA residues in soils. Extraction of solutes by soil sample was carried out by MAE for 20 min at 100 degrees C in the presence of 50 mL solution (methanol/water 50:50), the extract was subsequently passed through C18 cartidges and fractionated into two fractions, the first with parent compounds (PCs) analyzed with GC-MS and the second one containing the metabolites analyzed with HPLC. For the SPE step, various types of sorbents (Environmental C18, tC18, Supelclean ENVI-carb, and LiChrolut EN) have been used, and their respective advantages and disadvantages are discussed. After the method optimization, average recovery values of all solutes were > 71% in the 50-500 microg/kg fortification range with RSD <10%. The LOQ and LOD were 10-50 and 5-10 microg/kg, respectively. The method was validated with two types of soils (1 and 2.4% organic matter) and in fresh (12 h aging), intermediate (1 wk aging), and aged (1 month aging) spiked samples. Moreover, residue levels determined after field application of alachlor or metolachlor were higher when soils were processed using this method than with a comparison method based on an overnight flask shaking (FS) of soil suspension.

Determination of chloroacetanilides, triazines and phenylureas and some of their metabolites in soils by pressurised liquid extraction, GC–MS/MS, LC–MS and LC–MS/MS

Pressurised liquid extraction (PLE) technique was used for the simultaneous extraction of phenylureas, triazines and chloroacetanilides and some of their metabolites from soils. Extractions were performed by mixing 15 g of dried soil with 30 mL of acetone under 100 atm at 50 degrees C, during 3 min and with three PLE cycles. Prior to the analysis of naturally contaminated soils, each of the five representative soil matrices used as blanks (of different depths) was spiked in triplicate with standards of each parent and degradation compound at about 10, 30 and 120 microg/kg. For each experiment, isoproturon-D6 and atrazine-D5 were used as surrogates. Analysis of phenylureas and metabolites of triazines and phenylureas was carried out by reversed phase liquid chromatography/mass spectrometry (LC-MS) and LC-MS/MS in the positive mode. Gas chromatography (GC)/ion trap mass spectrometry was used in the MS/MS mode for the parent triazines and chloroacetanilides. The average extraction recoveries were above 85%, except for didesmethyl-isoproturon, and quantification limits were between 0.5 and 5 microg/kg. The optimised multi-residue method was applied to soils and solids below the root zone, sampled from agricultural plots of a small French hydrogeological basin.

Quantification of the new triketone herbicides, sulcotrione and mesotrione, and other important herbicides and metabolites, at the ng/l level in surface waters using liquid chromatography-tandem mass spectrometry

The LC/ESI/MSMS method allows the trace quantification (ng/l) of the new triketone herbicides, i.e. sulcotrione and mesotrione, and important herbicides and metabolites, in natural waters. Solid phase extraction (SPE) for sample enrichment is performed with OASIS (recoveries 94-112% for parent herbicides). Neutral and acidic compounds were analyzed separately with ESI in positive and negative mode, respectively. Quantification limits varied between 0.5 and 10 ng/l. The acidic herbicides detection was improved by a neutralizing post-column addition solution. The influence of ion suppression on quantification is discussed in detail. It is shown that we could overcome this problem and achieve reliable quantification using isotope labeled internal standards (ILIS) for every single analyte. The methods performance is illustrated with samples from a lake depth profile.

High-performance liquid chromatographic–nuclear magnetic resonance investigation of the isomerization of alachlor–ethanesulfonic acid

The metabolism of the acetanilide herbicide alachlor in soils leads to the formation of alachlor-ethanesulfonic acid (alachlor-ESA) as one of the major transformation products of this compound. The unique structure of alachlor and its metabolites allows the formation of two diastereomers (s-trans and s-cis) due to the hindered rotation of the amide bond connected to a rigid aromatic ring. Although these stereoisomers do interconvert by rotation about the amide bond, the rate of interconversion is slow allowing separation of the isomers on the chromatographic time scale. Once separated, the unique nuclear magnetic resonance signals of each isomer can be used to monitor the rate of isomerization. This paper reports the on-line separation and detection of the rotational diastereomers using high-performance liquid chromatography-nuclear magnetic resonance (HPLC-NMR) to efficiently measure the isomerization rate of alachlor-ESA.

Analytical method for the determination of metolachlor, acetochlor, alachlor, dimethenamid, and their corresponding ethanesulfonic and oxanillic acid degradates in water using SPE and LC/ESI-MS/MS

A Good Laboratory Practices (GLP) validated, multiresidue analytical method is presented for the determination of the chloroacetanilide herbicides metolachlor, acetochlor, and alachlor, the chloroacetamide herbicide dimethenamid, and their respective ethanesulfonic (ESA) and oxanillic (OA) acid degradates in ground and surface water. A 50-mL water sample is subjected to purification using a C-18 SPE column. The four parent components and their eight ESA and OA degradates are isolated using 80/20 methanol/water (v/v) for elution. The eluate is reduced to < 1.0 mL and reconstituted in 10/90 acetonitrile/water (v/v) to the desired final fraction volume. Final analysis is accomplished using liquid chromatography/electrospray ionization-mass spectrometry/mass spectrometry in the + (parent compounds) and - (ESA and OA degradates) ion modes by monitoring appropriate precursor/product ion pairs for each of the 12 analytes. The method limit of quantification is 0.10 ppb and the limit of detection is 0.125 ng injected for each analyte. Average procedural recovery data range from 95 to 105% for fortification levels of 0.10-100 ppb. The method validation study was performed following GLP guidelines.

Determination of oxanilic and sulfonic acid metabolites of acetochlor in soils by liquid chromatography-electrospray ionisation mass spectrometry

An analytical method is presented that describes the extraction and quantification of oxanilic and sulfonic acid metabolites of the herbicide acetochlor in soil samples. Experiments were performed on 50 g of soil using a solvent extraction technique with an acetonitrile-water (60:40) mixture in an acidic medium. Analysis was carried out by reversed-phase liquid chromatography and detection by electrospray ionisation mass spectrometry in single ion monitoring and negative modes. Four different soil matrices were spiked in triplicate with standards of each degradation compound at three concentration levels between 2 and 80 microg/kg. The average recoveries range from 90 to 120% for both the metabolites, with relative standard deviations lower than 15%. The limits of quantification are about 1 and 2 microg/kg for the ethanesulfonic acid and the oxanilic acid metabolites, respectively. The method has been applied to soils and solids recovered from the deeper unsaturated zone of a small French catchment closely monitored as part of the European project "Pesticides in European Groundwaters: detailed study of Aquifers and Simulation of possible Evolution scenarios (PEGASE)".

Analysis and detection of the herbicides dimethenamid and flufenacet and their sulfonic and oxanilic acid degradates in natural water

Dimethenamid [2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide] and flufenacet [N-(4-fluorophenyl)-N-(1-methylethyl)-2-(5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl)oxy] were isolated by C-18 solid-phase extraction and separated from their ethanesulfonic acid (ESA) and oxanilic acid (OXA) degradates during their elution using ethyl acetate for the parent compound, followed by methanol for the polar degradates. The parent compounds were detected using gas chromatography-mass spectrometry in selected-ion mode. The ESA and OXA degradates were detected using high-performance liquid chromatography--electrospray mass spectrometry (HPLC-ESPMS) in negative-ion mode. The method detection limits for a 123-mL sample ranged from 0.01 to 0.07 microg/L. These methods are compatible with existing methods and thus allow for analysis of 17 commonly used herbicides and 18 of their degradation compounds with one extraction. In a study of herbicide transport near the mouth of the Mississippi River during 1999 and 2000, dimethenamid and its ESA and OXA degradates were detected in surface water samples during the annual spring flushes. For flufenacet, the only detections at the study site were for the ESA degradates in samples collected at the peak of the herbicide spring flush in 2000. The low frequency of detections in surface water likely is due to dimethenamid and flufenacet being relatively new herbicides. In addition, detectable amounts of the stable degradates have not been detected in ground water.