Determination of glyphosate and aminomethylphosphonic acid in natural water using the capillary electrophoresis combined with enrichment step

A previously elaborated capillary electrophoresis (CE) method used for the determination of glyphosate and aminomethylphosphonic acid (AMPA) was slightly modified in order to improve the sensitivity. However, detection limits attained (5 μg mL⁻¹ for glyphosate and 4 μg mL⁻¹ for AMPA) were still not satisfactory for analytical purposes, thus the addition of a preconcentration step before the CE analysis was proposed. AMBERLITE^®IRA-900, a strong anion-exchange resin, was used to preconcentrate both analytes in environmental aqueous samples. The experimental conditions optimised in a previous work were readapted, by decreasing the eluent concentration due to CE limitations. Satisfactory results were attained when spiked ultrapure water was applied, with recoveries from 84 to 87% for glyphosate (R.S.D. < 6%) and from 85 to 98% for AMPA (R.S.D. < 5%). Enrichment factors up to 65 were achieved with this system, allowing the determination of 85 ng mL⁻¹ of glyphosate and 60 ng mL⁻¹ of AMPA. The extraction efficiency varied when four different natural water samples of varying conductivity were applied. Especially the strong dependence on ion concentration in samples on AMPA recovery was found. For glyphosate, good recoveries (86-99%) were obtained for samples of low and medium conductivity (0-800 μS). The effect of sample salt content on extraction efficiency was studied and a linear relationship could be established for AMPA (r² = 0.996). An important improvement on recoveries was observed when lower volumes of sample were treated.A HPLC method with UV-vis detection and pre-column derivatisation with p-toluensulphonyl chloride was compared to the CE method. No significant differences in results were found when t- and F-statistical tests were applied.     

In-capillary derivatization and laser-induced fluorescence detection for the analysis of organophosphorus pesticides by micellar electrokinetic chromatography

We developed a rapid and sensitive method using in-capillary derivatization and laser-induced fluorescence (LIF) detection for the fully automated analysis of organophosphorus pesticides (OPPs), including glufosinate, aminomethylphosphonic acid (AMPA) and glyphosate by micellar electrokinetic chromatography (MEKC). The potential of 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as in-capillary derivatization reagent is described for the first time. The unique feature of this MEKC method is the capillary being used as a small reaction chamber. In in-capillary derivatization, the sample and reagent solutions were injected directly into the capillary by tandem mode, followed by an electrokinetic step to enhance the mixing efficiency of analytes and reagent plugs in accordance with their different electrophoretic mobilities. Standing a specified time for reaction, the derivatives were then immediately separated and determined. Careful optimization of the derivatization and separation conditions allowed the determination of glufosinate, AMPA and glyphosate with detection limits of 2.8, 3.6 and 32.2 ng/mL, respectively. These detection limits were comparable to those of 1.4, 1.9 and 23.8 ng/mL obtained from conventional pre-capillary derivatization. Furthermore, repeatability better than 0.40% for migration time and 3.4% for peak area, as well as shorter migration time, was obtained. The method was successfully applied to the analysis of spiked river water sample with satisfactory results.     

Residue determination of glyphosate, glufosinate and aminomethylphosphonic acid in water and soil samples by liquid chromatography coupled to electrospray tandem mass spectrometry

This paper describes a method for the sensitive and selective determination of glyphosate, glufosinate and aminomethylphosphonic acid (AMPA) residues in water and soil samples. The method involves a derivatization step with 9-fluorenylmethylchloroformate (FMOC) in borate buffer and detection based on liquid chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS). In the case of water samples a volume of 10 mL was derivatized and then 4.3 mL of the derivatized mixture was directly injected in an on-line solid phase extraction (SPE)-LC-MS/MS system using an OASIS HLB cartridge column and a Discovery chromatographic column. Soil samples were firstly extracted with potassium hydroxide. After that, the aqueous extract was 10-fold diluted with water and 2 mL were derivatized. Then, 50 microL of the derivatized 10-fold diluted extract were injected into the LC-MS/MS system without pre-concentration into the SPE cartridge. The method has been validated in both ground and surface water by recovery studies with samples spiked at 50 and 500 ng/L, and also in soil samples, spiked at 0.05 and 0.5 mg/kg. In water samples, the mean recovery values ranged from 89 to 106% for glyphosate (RSD <9%), from 97 to 116% for AMPA (RSD < 10%), and from 72 to 88% in the case of glufosinate (RSD < 12%). Regarding soil samples, the mean recovery values ranged from 90 to 92% for glyphosate (RSD <7%), from 88 to 89% for AMPA (RSD <5%) and from 83 to 86% for glufosinate (RSD <6%). Limits of quantification for all the three compounds were 50 ng/L and 0.05 mg/kg in water and soil, respectively, with limits of detection as low as 5 ng/L, in water, and 5 microg/kg, in soil. The use of labelled glyphosate as internal standard allowed improving the recovery and precision for glyphosate and AMPA, while it was not efficient for glufosinate, that was quantified by external standards calibration. The method developed has been applied to the determination of these compounds in real water and soil samples from different areas. All the detections were confirmed by acquiring two transitions for each compound.     

直接进样超高效液相色谱-三重四极杆质谱法快速测定环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利残留

建立了一种简便、直接进样的超高效液相色谱-三重四极杆质谱法（UPLC-MS/MS）快速测定环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利的残留。环境水样经0.22 μm滤膜过滤或冷冻离心去除杂质后,滤液无需衍生化直接进行定量分析。4种农药通过Metrosep A Supp 5柱（150 mm×4.0 mm,5 μm）分离,以碳酸氢铵-氨水溶液为流动相进行梯度洗脱,在负离子模式下以MRM方式进行检测。结果表明,4种农药在0.50~50.0 μg/L范围内相关系数（r）均大于0.999,线性关系良好,方法检出限为0.05~0.09 μg/L。实际水样在低、中、高3种加标浓度水平下,回收率分别为76.3%~108%、83.0%~107%和87.0%~105%,相对标准偏差分别为2.0%~12.3%、2.4%~5.6%和2.7%~6.8%。使用该方法对海南省34个水样进行测定,其中30个饮用水源地水样中均未检出4种农药,槟榔园附近3个水样均检出草甘膦和氨甲基膦酸,香蕉园附近的1个水样检出草铵膦和氨甲基膦酸。与传统的衍生化方法比较,该方法操作简便,重现性好,准确性高,不受基体干扰,适用于环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利的残留检测。     

Determination of Glyphosate and Aminomethylphosphonic Acid in Water by LC Using a New Labeling Reagent, 4-Methoxybenzenesulfonyl Fluoride

A rapid, low-cost, and highly sensitive analytical method to detect glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA), in water samples has been developed, involving a derivatization with a new labeling reagent, 4-methoxybenzenesulfonyl fluoride, followed by reverse phase liquid chromatography with ultraviolet detection. The limits of detection of both of glyphosate and AMPA in real water samples are 0.1 μg L^?1 with simple pre-concentration. This method has proven to be sensitive and reliable for determination of glyphosate and AMPA in water samples.     

Rapid determination of glyphosate, glufosinate, bialaphos, and their major metabolites in serum by liquid chromatography-tandem mass spectrometry using hydrophilic interaction chromatography

We developed a simple and rapid method for the simultaneous determination of phosphorus-containing amino acid herbicides (glyphosate, glufosinate, bialaphos) and their major metabolites, aminomethylphosphonic acid (AMPA) and 3-methylphosphinicopropionic acid (MPPA), in human serum. Serum samples were filtrated through an ultrafiltration membrane to remove proteins. The filtrate was then washed with chloroform, and injected into a liquid chromatography-tandem mass spectrometry (LC-MS/MS) system. Chromatographic separation was achieved on a hydrophilic interaction chromatography (HILIC) column. Determination of the target herbicides and metabolites was successfully carried out without derivatization or solid phase extraction (SPE) cartridge clean-up. The recoveries of these compounds, added to human serum at 0.2μg/mL, ranged from 94% to 108%, and the relative standard deviations (RSDs) were within 5.9%. The limits of detection (LODs) were 0.01μg/mL for MPPA, 0.02μg/mL for AMPA, 0.03μg/mL for both glyphosate and glufosinate, and 0.07μg/mL for bialaphos, respectively.     

Ultratrace-level determination of glyphosate,aminomethylphosphonic acid and glufosinate in natural waters by solid-phase extraction followed by liquid chromatography–tandem mass spectrometry: performance tuning of derivatization,enrichment and detection

A sensitive and robust analytical method for the quantification of glyphosate, aminomethylphosphonic acid (AMPA) and glufosinate in natural water has been developed on the basis of a derivatization with 9-fluorenylmethylchloroformate (FMOC-Cl), solid-phase extraction (SPE) and liquid chromatography followed by electrospray tandem mass spectrometry (LC-ESI-MS/MS). In order to maximize sensitivity, the derivatization was optimized regarding organic solvent content, amount of FMOC-Cl and reaction time. At an acetonitrile content of 10% a derivatization yield of 100% was reached within two hours in groundwater and surface water samples. After a twofold dilution the low acetonitrile content allowed solid-phase extraction of a sample of originally 80 mL over 200 mg Strata-X cartridges. In order to decrease the load of the LC column and mass spectrometer with derivatization by-products (e.g., 9-fluorenylmethanol FMOC-OH), a rinsing step was performed for the SPE cartridge with dichloromethane. Acidification of the sample and addition of EDTA was used to minimize complexation of the target compounds with metal ions in environmental samples. Due to the large sample volume and the complete FMOC-OH removal, limits of quantification of 0.7 ng/L, 0.8 ng/L and 2.3 ng/L were achieved in surface water for glyphosate, AMPA and glufosinate, respectively. The limits of detection were as low as 0.2 ng/L, 0.2 ng/L and 0.6 ng/L for glyphosate, AMPA and glufosinate, respectively. Surface water and ground water samples spiked at 2 ng/L showed recoveries of 91–107%. Figure LC-MS/MS chromatogram of a water sample from a remote alpine region spiked at 1 ng/L     

Qualitative/quantitative strategy for the determination of glufosinate and metabolites in plants

A simple method for the simultaneous determination of glufosinate and its metabolites in plants based on liquid chromatography–ultraviolet (LC–UV) absorption detection after derivatization with fluorenylmethoxycarbonyl chloride (FMOC-Cl) of some analytes to facilitate separation is reported here. Nonavailable standard metabolites were identified by LC–TOF/mass spectrometry (MS), which also confirmed all target analytes. Ultrasound-assisted extraction was used for sample preparation (power of 70 W and duty cycle of 0.7 s/s for 10 min) with subsequent evaporation of the extractant, reconstitution and filtration as the cleanup/concentration step prior to derivatization, and chromatographic separation and detection at 270 nm for underivatized analytes and 340 nm for those that were derivatized. The chromatographic analysis was completed in 40 min using a Luna® column (C18 phase). The analytical characteristics of the method were linear dynamic range of the calibration curves within 0.047–700 μg/mL with a regression coefficient (rc) of 0.999 for glufosinate, 0.077–700 μg/mL with a rc of 0.998 for N-acetyl-glufosinate, and 0.116–600 μg/mL with a rc of 0.998 for 3-(methylphosphinico)propanoic acid. The precision for the determination of glufosinate (studied at two levels, 0.1 and 5 μg/mL) was 2.7 and 6.0 % for repeatability and 4.7 and 7.2 % for within-laboratory reproducibility, respectively. Identification and confirmatory analysis of the presence of glufosinate and metabolites in the extracts from treated plants was carried out by LC–TOF/MS in high-resolution mode for the precursor ion. The method was validated by analyzing wheat (Triticum aestivum) samples (resistant and susceptible biotypes) treated with 300 g of glufosinate/ha following conventional agronomical practices.     

In situ derivatization and hollow fiber membrane microextraction for gas chromatographic determination of haloacetic acids in water

An alternative method for gas chromatographic determination of haloacetic acids (HAAs) in water using direct derivatization followed by hollow fiber membrane liquid-phase microextraction (HF-LPME) has been developed. The method has improved the sample preparation step according to the conventional US EPA Method 552.2 by combining the derivatization and the extraction into one step prior to determination by gas chromatography electron captured detector (GC-ECD). The HAAs were derivatized with acidic methanol into their methyl esters and simultaneously extracted with supported liquid hollow fiber membrane in headspace mode. The derivatization was attempted directly in water sample without sample evaporation. The HF-LPME was performed using 1-octanol as the extracting solvent at 55 °C for 60 min with 20% Na₂SO₄. The linear calibration curves were observed for the concentrations ranging from 1 to 300 μg L⁻¹ with the correlation coefficients (R²) being greater than 0.99. The method detection limits of most analytes were below 1 μg L⁻¹ except DCAA and MCAA that were 2 and 18 μg L⁻¹, respectively. The recoveries from spiked concentration ranged from 97 to 109% with %R.S.D. less than 12%. The method was applied for determination of HAAs in drinking water and tap water samples. The method offers an easy one step high sample throughput sample preparation for gas chromatographic determination of haloacetic acids as well as other contaminants in water.     

An amperometric method for the detection of amitrole, glyphosate and its aminomethyl-phosphonic acid metabolite in environmental waters using passive samplers

The herbicides amitrole and glyphosate, and its metabolite aminomethyl-phosphonic acid (AMPA), in water samples have been directly analysed by high-performance liquid chromatography using an electrochemical (EC) detector. Limits of detection of 0.3 μg mL⁻¹ for glyphosate, 0.05 μg mL⁻¹ for AMPA and 0.03 μg mL⁻¹ for amitrole were comparable to those obtained by other authors using EC and also by liquid chromatography coupled to mass spectrometry, but the latter method requires derivatisation and pre-concentration of the sample whereas EC methods show similar sensitivity without the need of any derivatisation. The method was specifically designed to analyse extracts from passive samplers used for monitoring of polar herbicide residues in waters. To this purpose, three types of Empore^® disks were tested for their ability to adsorb and desorb these ionic, polar analytes. A procedure for their extraction from the membranes and reducing the interferences from other substances present in natural waters (i.e. humic acids) is described. The method is simple, does not require sophisticated equipment and is valid for the analysis and monitoring of herbicides residues using passive samplers.     

Determination of imipramine and trimipramine by capillary electrophoresis with electrochemiluminescence detection

The tricyclic antidepressants (TCA) imipramine (Imi) and trimipramine (Tri) were successfully analyzed by capillary electrophoresis (CE) coupling with Tris(2,2-bipyridyl) ruthenium(II)-based (Ru(bpy)₃²⁺) end-column electrochemiluminescence (ECL) detection. The addition of β-CD to the running buffer was found to enable baseline separation of the two analytes and the addition of acetonitrile (ACN) as an organic additive to improve the repeatability and sensitivity of the CE method. Under the optimized separation and detection conditions (50 mM PBS (pH = 7.0) and 2 mM Ru(bpy)₃²⁺ in the ECL detection cell, 20 mM Tris (pH = 2.0), 0.2 mM β-CD and 20% ACN (v/v) as running buffer), wide linear ranges of 0.1-5 μM and 0.1-5 μM were achieved, with the correlation coefficients of 0.9990 (n = 8) and 0.9980 (n = 8) for Imi and Tri, respectively. Detection limits 5 nM and 1 nM (S/N = 3) were obtained for Imi and Tri, respectively. The method was also successfully applied for the determination of Imi in pharmaceutical dosage form.     

Dynamic supported liquid membrane tip extraction of glyphosate and aminomethylphosphonic acid followed by capillary electrophoresis with contactless conductivity detection

A dynamic supported liquid membrane tip extraction (SLMTE) procedure for the effective extraction and preconcentration of glyphosate (GLYP) and its metabolite aminomethylphosphonic acid (AMPA) in water has been investigated. The SLMTE procedure was performed in a semi-automated dynamic mode and demonstrated a greater performance against a static extraction. Several important extraction parameters such as donor phase pH, cationic carrier concentration, type of membrane solvent, type of acceptor stripping phase, agitation and extraction time were comprehensively optimized. A solution of Aliquat-336, a cationic carrier, in dihexyl ether was selected as the supported liquid incorporated into the membrane phase. Quantification of GLYP and AMPA was carried out using capillary electrophoresis with contactless conductivity detection. An electrolyte solution consisting of 12 mM histidine (His), 8 mM 2-(N-morpholino)ethanesulfonic acid (MES), 75 μM cetyltrimethylammonium bromide (CTAB), 3% methanol, pH 6.3, was used as running buffer. Under the optimum extraction conditions, the method showed good linearity in the range of 0.01–200 μg/L (GLYP) and 0.1–400 μg/L (AMPA), acceptable reproducibility (RSD 5–7%, n = 5), low limits of detection of 0.005 μg/L for GLYP and 0.06 μg/L for AMPA, and satisfactory relative recoveries (90–94%). Due to the low cost, the SLMTE device was disposed after each run which additionally eliminated the possibility of carry-over between runs. The validated method was tested for the analysis of both analytes in spiked tap water and river water with good success.     

Simultaneous Determination of Glyphosate,Glufosinate, and Aminomethylphosphonic Acid by Capillary Electrophoresis After 9‐Fluorenylmethyl Chloroformate Derivatization

A capillary electrophoresis (CE) with UV absorption detection method is described for the simultaneous determination of glufosinate, glyphosate, and aminomethylphosphoric acid. The 9‐fluorenylmethyl chloroformate (FMOC‐Cl) was used for precolumn derivatization of the non‐absorbing herbicides. The three analytes were separated by CE in 9 min with 25 mM borate buffer at pH 9, followed by detection with a UV detector at 260 nm. We demonstrate how the detection limit can be enhanced by using acetonitrile‐salt mixtures. With acetonitrile‐salt mixtures, the limit of detection (LOD) was in the 10^?7 M range. Linearity of more than two orders of magnitude was generally obtained. Precisions of migration times and peak areas were less than 0.9% and 7.5%, respectively. The applicabilities of the method for the analysis of ground water and lake water were examined.     

Automated trace level determination of glyphosate and aminomethyl phosphonic acid in water by on-line anion-exchange solid-phase extraction followed by cation-exchange liquid chromatography and post-column derivatization.

An automated method based on the on-line coupling of anion-exchange solid-phase extraction (SPE) and cation-exchange liquid chromatography followed by post-column derivatization and fluorescence detection has been developed for the trace level determination of glyphosate and its primary conversion product aminomethyl phosphonic acid (AMPA) in water. PRP-X100 poly(styrene-divinylbenzene)-trimethylammonium anion-exchange cartridges (20 x 2 mm, 10 microm) were selected for the SPE of glyphosate and AMPA. The ionic compounds present in the samples strongly influenced the extraction of both analytes; however, when an on-line ion-exchange clean-up step was introduced before sample SPE, the problem was largely solved. By processing 100-ml samples detection limits better than 0.02 microg/l for glyphosate and 0.1 microg/l for AMPA were achieved in river water. Both analytes were unstable in solution and the approach of storing samples on the PRP-X100 SPE cartridges was evaluated for a period of 1 month under three different storage conditions (deep freeze, refrigeration and 20 degrees C).     

Rapid and direct determination of glyphosate,glufosinate, and aminophosphonic acid by online preconcentration CE with contactless conductivity detection

Rapid and direct online preconcentration followed by CE with capacitively coupled contactless conductivity detection (CE‐C⁴D) is evaluated as a new approach for the determination of glyphosate, glufosinate (GLUF), and aminophosphonic acid (AMPA) in drinking water. Two online preconcentration techniques, namely large volume sample stacking without polarity switching and field‐enhanced sample injection, coupled with CE‐C⁴D were successfully developed and optimized. Under optimized conditions, LODs in the range of 0.01–0.1 μM (1.7–11.1 μg/L) and sensitivity enhancements of 48‐ to 53‐fold were achieved with the large volume sample stacking‐CE‐C⁴D method. By performing the field‐enhanced sample injection‐CE‐C⁴D procedure, excellent LODs down to 0.0005–0.02 μM (0.1–2.2 μg/L) as well as sensitivity enhancements of up to 245‐ to 1002‐fold were obtained. Both techniques showed satisfactory reproducibility with RSDs of peak height of better than 10%. The newly established approaches were successfully applied to the analysis of glyphosate, glufosinate, and aminophosphonic acid in spiked tap drinking water.     

Simultaneous Derivatization and Dispersive Liquid–Liquid Microextraction for Fatty Acid GC Determination in Water

Simultaneous derivatization and dispersive liquid–liquid microextraction technique for gas chromatographic determination of fatty acids in water samples is presented. One hundred microlitre of ethanol:pyridine (4:1) were added to 4 mL aqueous sample. Then a solution containing 0.960 mL of acetone (disperser solvent), 10 μL of carbon tetrachloride (extraction solvent) and 30 μL of ethyl chloroformate (derivatization reagent) were rapidly injected into the aqueous sample. After centrifugation, 1 μL sedimented phase with the analytes was analyzed by gas chromatography. The effects of extraction solvent type, derivatization, extraction, and disperser solvents volume, extraction time were investigated. The calibration graphs were linear up to 10 mg L^?1 for azelaic acid (R ² = 0.998) and up to 1 mg L^?1 for palmitic and stearic acids (R ² = 0.997). The detection limits were 14.5, 0.67 and 1.06 μg L^?1 for azelaic, palmitic, and stearic acids, respectively. Repeatabilities of the results were acceptable with relative standard deviations (RSD) up to 13%. A possibility to apply the proposed method for fatty acids determination in tap, lake, sea, and river water was demonstrated.     

Simultaneous fluorimetric determination of glyphosate and its metabolite, aminomethylphosphonic acid, in water, previous derivatization with NBD-Cl and by partial least squares calibration (PLS)

The reactions of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with glyphosate (GLY) and with its main metabolite, aminomethylphosphonic acid (AMPA), have been studied. The resolution of binary mixtures of glyphosate and aminomethylphosphonic acid has been accomplished by partial least squares (PLS) multivariate calibration. The method of determination is based on the fluorescence emission of the derivatives formed in presence of NBD-Cl at 90 °C, in methanol and in basic medium. The dynamic ranges of the methods were comprised between 10 and 150 μg l⁻¹ for GLY and between 10 and 200 μg l⁻¹ for AMPA, being the detection limits 2 and 5.4 μg l⁻¹ for GLY and AMPA, respectively. The total luminiscence information of the derivatives has been used to optimize the spectral data set to perform the calibration, by analysis of the three-dimensional excitation-emission matrices. A comparison between the predictive ability of the multivariate calibration method, partial least squares type 1 (PLS-1), on two spectral data sets, emission and synchronous spectra, has been performed. The PLS-1 method, applied to the emission spectra, has been selected as optimum. The proposed method has been applied to the simultaneous determination of GLY and AMPA in river water. For concentrations ranging from 100 to 600 μg l⁻¹ of each compound in the samples, analytical recoveries range from 83 to 94% for GLY and from 104 to 120% for AMPA.     

Improved coupled-column liquid chromatographic method for the determination of glyphosate and aminomethylphosphonic acid residues in environmental waters

An existing method for the determination of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in water has been improved. It is based on precolumn derivatization with the fluorescent reagent 9-fluorenylmethylcloroformate (FMOC) followed by large-volume injection in a coupled-column LC system using fluorescence detection (LC-LC-FD). The derivatization step was slightly modified by changing parameters such as volume and/or concentration of sample and reagents to decrease the limits of quantification (LOQ) of glyphosate and AMPA to 0.1 microg/l. Additionally, the use of Amberlite IRA-900 for preconcentration of glyphosate, prior to the derivatization step, was investigated; the LOQ of glyphosate was lowered to 0.02 microg/l. Drinking, surface and ground water spiked with glyphosate and AMPA at 0.1-10 microg/l concentrations were analysed by the improved LC-LC-FD method. Recoveries were 87-106% with relative standard deviations lower than 8%. Drinking and ground water spiked with glyphosate at 0.02 and 0.1 microg/l were analysed after preconcentration on the anion-exchange resin with satisfactory recoveries (94-105%) and precision (better than 8%).     

Determination of geosmin and 2-methylisoborneol in water and wine samples by ultrasound-assisted dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry

A fast, simple and environmentally friendly ultrasound-assisted dispersive liquid–liquid microextraction (USADLLME) procedure has been developed to preconcentrate geosmin and 2-methylisoborneol (MIB) from water and wine samples prior to quantification by gas chromatography–mass spectrometry (GC–MS). A two-stage multivariate optimization approach was developed by means of a Plackett–Burman design for screening and selecting the significant variables involved in the USADLLME procedure, which was later optimized by means of a circumscribed central composite design. The optimum conditions were: solvent volume, 8 μL; solvent type: tetrachloroethylene; sample volume, 12 mL; centrifugation speed, 2300 rpm; extraction temperature 20 °C; extraction time, 3 min; and centrifugation time, 3 min. Under the optimized experimental conditions the method gave good levels of repeatability with coefficient of variation under 11% (n = 10). Limits of detection were 2 and 9 ng L⁻¹ for geosmin and MIB, respectively. Calculated calibration curves gave high levels of linearity with correlation coefficient values of 0.9988 and 0.9994 for geosmin and MIB, respectively. Finally, the proposed method was applied to the analysis of two water (reservoir and tap) samples and three wine (red, rose and white) samples. The samples were previously analyzed and confirmed free of target analytes. Recovery values ranged between 70 and 113% at two spiking levels (0.25 μg L⁻¹ and 30 ng L⁻¹) showing that the matrix had a negligible effect upon extraction. Only red wine showed a noticeable matrix effect (70–72% recovery). Similar conclusions have been obtained from an uncertainty budget evaluation study.     

Determination of glyphosate and aminomethylphosphonic acid in aqueous soil matrices: A critical analysis of the 9‐fluorenylmethyl chloroformate derivatization reaction and application to adsorption studies

The assessment of the environmental fate of glyphosate and its degradation product (aminomethylphosphonic acid) is of great interest given the widespread use of the herbicide. Studies of adsorption–desorption and transport processes in soils require analytical methods with sensitivity, accuracy, and precision suitable for determining the analytes in aqueous equilibrium solutions of varied complexity. In this work, the effect of factors on the yield of the derivatization of both compounds with 9‐fluorenylmethyl chloroformate for applying in aqueous solutions derived from soils was evaluated through factorial experimental designs. Interference effects coming from background electrolytes and soil matrices were established. The whole method had a linear response up to 640 ng/mL (R² > 0.999) under optimized conditions for high‐performance liquid chromatography with fluorescence detection. Limits of detection were 0.6 and 0.4 ng/mL for glyphosate and aminomethylphosphonic acid, respectively. The relative standard deviation was 4.4% for glyphosate (20 ng/mL) and 5.9% for aminomethylphosphonic acid (10 ng/mL). Adsorption of compounds on four different soils was assessed. Isotherm data fitted well the Freundlich model (R² > 0.97). K_f constants varied between 93 ± 3.1 and 2045 ± 157 for glyphosate and between 99 ± 4.1 and 1517 ± 56 (μg^1‐1/n mL^1/n g^–1) for aminomethylphosphonic acid, showing the broad range of applicability of the proposed method.