Micro-scale membrane extraction of glyphosate and aminomethylphosphonic acid in water followed by high-performance liquid chromatography and post-column derivatization with fluorescence detector

High performance liquid chromatography coupled with post - Column derivatization methods in food analysis: Chemistries and applications in the last two decades

High performance liquid chromatography coupled with post-column derivatization is used for increasing the sensitivity and selectivity of the desirable analytes after the chromatographic separation. The transformation of the analytes can be conducted through the addition of a suitable reagent in the eluted stream or the ultraviolet irradiation of the eluted analytes, forming detectable derivatives for ultraviolet or fluorescence detectors. This review focuses on the developed methods using high performance liquid chromatography coupled with post-column derivatization for the determination of substances in food samples during the last two decades. The significance of the determination of each analyte in foods and the existing guidelines in each case are discussed. Preparation of the samples and the analytical methods are commented. For each analyte, official methods and commercially available systems and reagents are mentioned, as well.

Magnetic Molecularly Imprinted Polymer for the Selective Enrichment of Glyphosate, Glufosinate, and Aminomethylphosphonic Acid Prior to High-Performance Liquid Chromatography

A novel mixed iron hydroxide molecularly imprinted polymer (MIH-MIP) was synthesized via polymerization using mixed-valence iron hydroxide as a magnetic supporter, glyphosate as a template, acrylamide as a functional monomer, and ethylene glycol dimethacrylate as a cross-linker. The resulting material was characterized and applied as a sorbent for the selective enrichment of glyphosate, aminomethylphosphonic acid, and glufosinate by magnetic solid-phase extraction (MSPE) prior to high-performance liquid chromatography. MIH-MIP possessed a high adsorption capacity in the range of 2.31-5.40 mg g^-1 with good imprinting factors ranging from 1.52 to 7.59. The Langmuir model proved that the recognition sites were distributed as a monolayer on the surface of MIH-MIP. Scatchard analysis showed two types of binding sites on MIH-MIP. The kinetic characteristics of MIH-MIP suggested that the binding process of all analytes fit well with the pseudosecond-order model. The developed methodology provides good linearity in the range of 72.0-2000.0 μg L^-1. Low detection limits of 21.0-22.5 μg L^-1 and enrichment factors of up to 18 were achieved. The precision in terms of relative standard deviations of the intra- and interday experiments was better than 7 and 9%, respectively. The applicability of the developed MSPE facilitates the accurate and efficient determination of water, soil, and vegetable samples with satisfactory recoveries in the range of 86-118%. The results confirmed the suitability of the MIH-MIP sorbent for selective extraction and quantification of glyphosate, aminomethylphosphonic acid, and glufosinate.

Carrier-mediated extraction: Applications in extraction and microextraction methods

The present review is mainly focused on the overview of carrier mediated extraction (principles and applications) being reported over the last two decades and discusses the extraction process through carriers in various extraction methods such as Bulk liquid membranes, supported liquid membranes, emulsion liquid membranes and polymer inclusion membranes. Several types of carriers such as neutral, anionic, cationic, macrocyclic and supramulecular carriers are discussed. Also their application for metal, anions, drugs and environmental compounds are investigated. Carriers have been demonstrated to be useful for the selective extraction and recovery of numerous cations and anions enhancing the extraction properties of traditional solvent extraction and ion-exchange processes. Several types of carriers have different transport mechanisms. In these mechanisms, transport configurations are addressed and emphasized and the detailed information on the type of carrier are presented along with their specific separation modes. The performance of different carriers in terms of selectivity as well as efficiency are also discussed. Finally, the application of different carriers for the extraction of various compounds are compared and reviewed. To our best knowledge no reviews have been published on carrier-mediated extraction methods.

A novel fluorimetric method for glyphosate and AMPA determination with NBD-Cl and MCR-ALS

We report the development of a new analytical method for the quantification of N-(phosphonomethyl)glycine (glyphosate) and (aminomethyl)phosphonic acid (AMPA) by combining spectrofluorimetry and multivariate calibration. In this study, fluorescence spectroscopy was used to quantify glyphosate and AMPA, which were previously derivatized with the fluorogenic reagent: 4-chloro-7-nitrobenzofurazan (NBD-Cl). Fluorescence excitation-emission matrices (EEM) were recorded by exciting between 400 and 500 nm, and measuring the emission between 500 and 610 nm. The second-order data obtained were processed using the Multivariate Curve Resolution with Alternating Least Square (MCR-ALS) methodology. The developed method was used to predict different concentrations of glyphosate and AMPA in validation samples. In addition, the presence of the herbicide was evaluated in real samples: a commercial formulation and a water sample from a cultivated area. For this purpose, the standard addition method was used to study the matrix effect in each case. The ranges of working concentrations obtained for this new method are in agreement with the amounts found in surface water samples near a direct sowing soybean growing region in Argentina.

DLLME-spectrophotometric determination of glyphosate residue in legumes

A new separation and pre-concentration method for spectrophotometric determination of glyphosate herbicide was developed. Glyphosate was converted into dithiocarbamic acid with CS2, followed by copper in the presence of ammonia to promote complex formation. This complex was collected in a CH2Cl2 organic drop and absorbance measured at 435nm. The analytical parameters, such as the amount of NH3, Cu(II) and CS2, type of extraction solutions, and the ratio of dispersive and organic liquids were optimized. The calibration curve was linear in the range 0.5-10mgl-1. The limits of detection and quantification were calculated from 3s to 10s criterions as 0.21mgl-1 and 0.70mgl-1, respectively. The developed method was applied to legume samples with the satisfactory recovery values of 98±4-102±3%.

Development and Validation of Ion Chromatography-Tandem Mass Spectrometry-Based Method for the Multiresidue Determination of Polar Ionic Pesticides in Food

An extraction method using acidified methanol based on the quick polar pesticide (QuPPe) method using suppressed ion chromatography coupled to mass spectrometry was developed and validated for the direct analysis of polar pesticides, without the need for derivatization or ion pairing, in cereals and grapes. The method was robust, and results for glyphosate, aminomethyl phosphonic acid (AMPA), N-acetyl-AMPA, glufosinate, 3-methylphosphinicopropionic acid (3-MPPA), N-acetyl glufosinate, ethephon, chlorate, perchlorate, fosetyl aluminum, and phosphonic acid at three concentration levels (typically 0.01, 0.05, and 0.1 mg/kg) were compliant with SANTE/11945/2015 guideline method performance criteria. Cereal-based infant food proved to be a more challenging matrix and validated only for glyphosate, chlorate, and perchlorate at 0.005, 0.01, and 0.05 mg/kg. The developed method enables the multiresidue analysis of 12 ionic pesticides and relevant metabolites in a single analysis. Until now, the analysis of these compounds required several different single-residue methods using different chromatographic conditions. This multiresidue approach offers the possibility of more cost-effective and more efficient monitoring of polar ionic pesticides and contaminants that are of concern to food regulation bodies and consumers.

Mg2+ ion as a tuner for colorimetric sensing of glyphosate with improved sensitivity via the aggregation of 2-mercapto-5-nitrobenzimidazole capped silver nanoparticles

The sensitivity of MNBZ-Ag NPs was greatly improved by integrating Mg²⁺ ion as trigger that can capture the glyphosate at nanomolar concentration with high selectivity.

Molecularly imprinted polymer dedicated to the extraction of glyphosate in natural waters

Three molecularly imprinted polymers (MIPs) have been synthesized in order to bind efficiently glyphosate (GLY) in natural waters (mineral and underground). Since the target analyte is polar and hydrophilic, electrostatic interactions and hydrogen bonds have been favored with two templates (phenylphosphonic acid and diethyl(α-aminobenzyl)-phosphonic acid) and two functional monomers (1-allyl-2-thiourea and methacrylic acid). MIPs have been assessed by comparison of the recoveries obtained with MIP and NIP (non imprinted polymer) by solid-phase extraction (SPE). The selectivity of MIP versus NIP was satisfactory for the three imprinted polymers with a very straightforward protocol: conditioning of 250 mg of MIP or NIP packed in 3-mL polypropylene cartridges with 3 mL Milli-Q water, loading of Milli-Q water (15 mL) spiked with 5 mg L(-1) of GLY and its metabolite, aminomethylphosphonic acid (AMPA) and elution by 3 mL NH4OH (10mM) or 3 mL HCl (100mM). SPE fractions were directly analyzed by capillary electrophoresis (CE). Thus, the recoveries of both analytes were greater than 80% for all MIPs and less than 25% for most NIPs. Moreover, the MIP prepared with 1-allyl-2-thiourea as functional monomer and phenylphosphonic acid as template displayed a capacity of 0.033 μmol/mg for GLY. However, the substitution of Milli-Q water by mineral water caused the decrease of MIP recoveries, for that, a pretreatment of the sample by ionic exchange resins was set up and succeeded in improving recoveries (about 50% for GLY and 25% for AMPA). Then, groundwaters were spiked with low concentrations of GLY and AMPA (0.5 μgL(-1)) and directly percolated through MIP cartridges. The extractions were carried out by triplicate and the elution fractions were analyzed by UPLC-MS/MS. The results showed no retention of AMPA but a total retention of GLY by MIP.

Efficient fluorescence resonance energy transfer between oppositely charged CdTe quantum dots and gold nanoparticles for turn-on fluorescence detection of glyphosate

We designed a turn-on fluorescence assay for glyphosate based on the fluorescence resonance energy transfer (FRET) between negatively charged CdTe quantum dots capped with thioglycolic acid (TGA-CdTe-QDs) and positively charged gold nanoparticles stabilized with cysteamine (CS-AuNPs). Oppositely charged TGA-CdTe-QDs and CS-AuNPs can form FRET donor-acceptor assemblies due to electrostatic interactions, which effectively quench the fluorescence intensity of TGA-CdTe-QDs. The presence of glyphosate could induce the aggregation of CS-AuNPs through electrostatic interactions, resulting in the fluorescence recovery of the quenched QDs. This FRET-based method has been successfully utilized to detect glyphosate in apples with satisfactory results. The detection limit for glyphosate was 9.8 ng/kg (3σ), with the linear range of 0.02-2.0 μg/kg. The attractive sensitivity was obtained due to the efficient FRET and the superior fluorescence properties of QDs. The proposed method is a promising approach for rapid screening of glyphosate in real samples.

Fast and interference-free determination of glyphosate and glufosinate residues through electrophoresis in disposable microfluidic chips

With an increasing concern on food safety, fast screening of residues of widespread herbicides becomes necessary. Herein we report a microchip electrophoresis system with laser induced fluorescence (LIF) detection for rapid and sensitive analysis of glyphosate (GLYP) and glufosinate (GLUF) residues. Disposable cyclic olefin copolymer microchips and a low-cost LIF detector were employed to minimize the cost of the analysis. Systematic optimization of experimental conditions was performed to achieve highly efficient analysis. Under the selected condition, GLYP and GLUF were efficiently resolved from sample matrices with a buffer containing 10 mmol/L borax and 2.0% (m/v) hydroxypropyl cellulose at pH 9.0. The number of theoretical plates of 1.0×10(6) m(-1) was attained for both analytes. Derivatization at lower concentrations (<10 μg/L) was also examined, successful detection of 0.34 μg/L GLYP and 0.18 μg/L GLUF was confirmed. The system was applied for the determination of both analytes in real samples without any preconcentration involved. Recoveries of GLYP and GLUF spiked in these samples were 84.0-101.0% and 90.0-103.0%, respectively.

Direct determination of glyphosate and its major metabolite, aminomethylphosphonic acid, in fruits and vegetables by mixed-mode hydrophilic interaction/weak anion-exchange liquid chromatography coupled with electrospray tandem mass spectrometry

A novel method was developed for the direct, sensitive, and rapid determination of glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA), in fruit and vegetable samples by mixed-mode hydrophilic interaction/weak anion-exchange liquid chromatography (HILIC/WAX) coupled with electrospray tandem mass spectrometry (ESI-MS/MS). Homogenized samples were extracted with water, without derivatization or further clean-up, and the extracts were injected directly onto the Asahipak NH2P-50 4E column (250 mm × 4.6 mm i.d., 5 μm). The best results were obtained when the column was operated under mixed-mode HILIC/WAX elution conditions. An initial 10-min washing step with acetonitrile/water (10:90, v/v) in HILIC mode was used to remove potentially interfering compounds, and then the analytes were eluted in WAX mode with acetonitrile and water containing 0.1 molL(-1) ammonium hydroxide under gradient elution for the ESI analysis in negative ion mode. Limits of quantification of glyphosate and AMPA were 5 μgkg(-1) and 50 μgkg(-1), respectively, with limits of detection as low as 1.2 μgkg(-1) for glyphosate and 15 μgkg(-1) for AMPA. The linearity was satisfactory, with correlation coefficients (r)>0.9966. Recovery studies were carried out on spiked matrices (6 vegetables, 3 fruits) with glyphosate at four concentrations and AMPA at three concentrations. The mean recoveries for glyphosate and AMPA were 75.3-110% and 76.1-110%, respectively, with relative standard deviations in the range of 1.1-13.8%. The intra-day precision (n=7) for glyphosate and AMPA in vegetable and fruit samples spiked at an intermediate level between 5.9% and 7.5%, and the inter-day precision over 11 days (n=11) was between 7.0% and 13%.

Trace analysis of glyphosate in water by capillary electrophoresis on a chip with high sample volume loadability

A new method for the determination of trace glyphosate (GLYP), non-selective pesticide, by CZE with online ITP pre-treatment of drinking waters on a column-coupling (CC) chip has been developed. CC chip was equipped with two injection channels of 0.9 and 9.9 μL volumes, two separation channels of 9.3 μL total volume and a pair of conductivity detectors. A very effective ITP sample clean-up performed in the first channel at low pH (3.2) was introduced for quick CZE resolution and detection of GLYP carried out at higher pH (6.1) in the second channel on the CC chip. The LOD for GLYP was estimated at 2.5 μg/L (15 nmol/L) using a 9.9 |mL volume of the injection channel. ITP-CZE analyses of model and real samples have provided very favorable intra-day (0.1-1.2% RSD) and inter-day (2.9% RSD) repeatabilities of the migration time for GLYP while 0.2-6.9% RSD values were typical for the peak area data. Recoveries of GLYP in spiked drinking water varied in the range of 99-109%. A minimum pre-treatment of drinking water (degassing and dilution) and a short analysis time (ca. 10 min) were distinctive features of ITP-CZE determinations of GLYP on the CC chip with high sample volume loaded, as well.

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 microM 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 microg/L (GLYP) and 0.1-400 microg/L (AMPA), acceptable reproducibility (RSD 5-7%, n=5), low limits of detection of 0.005 microg/L for GLYP and 0.06 microg/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.

Effect of suppressor current intensity on the determination of glyphosate and aminomethylphosphonic acid by suppressed conductivity ion chromatography

This paper presents the application of ion chromatography with electrolytic eluent generation and mobile phase suppression for the direct conductimetric detection of glyphosate and its degradation product aminomethylphosphonic acid (AMPA). The compounds were separated on a Dionex AS18 anion exchange column with a 12-40 mM KOH step gradient from 9 to 9.5 min. The effect of the suppressor current intensity on the electrostatic interaction of these amphoteric compounds with the suppressor cation exchange membranes was evaluated. A suppressor current gradient technique was proposed for the limitation of peak broadening and baseline noise, in order to improve method sensitivity and detectability. It was observed that residual sample carbonates co-eluted with AMPA when a large injection loop was installed for the low level determination of both compounds in natural waters. For this reason, glyphosate was isocratically eluted using 33 mM KOH in order to decrease analysis time within 10 min and a column clean up step using 100 mM KOH was used to ensure retention time reproducibility. The developed method was applied to the analysis of drinking and natural water and it was further successfully applied to orange samples with slight modifications. Instrumental LOD for glyphosate was 0.24 microg/L, while method LOD was 0.54 microg/L for spring waters and 0.01 mg/kg for oranges using a 1000 microL direct loop injection of the sample. Intra-day and inter-day precision (as %RSD) for water samples was 4.6% and 12% at a spiking level of 2 microg/L, and the recovery ranged from 64% to 88% depending on sample conductivity. For orange samples, the inter-day precision was 1.4% at a spiking level of 4.4 mg/kg, while overall recovery was 103%. The developed method is direct, fast, sensitive and relatively inexpensive, and could be used as an ideal fast screening tool for the monitoring of glyphosate residues in water and fruit samples.

Microscale solid phase extraction of glyphosate and aminomethylphosphonic acid in water and guava fruit extract using alumina-coated iron oxide nanoparticles followed by capillary electrophoresis and electrochemiluminescence detection

A microscale solid-phase extraction (SPE) method using alumina-coated iron oxide nanoparticles (Fe(3)O(4)@Al(2)O(3) NPs) as the affinity adsorbent for glyphosate (GLY) and its major metabolite aminomethylphosphonic acid (AMPA) in aqueous solution is reported. One milligram of Fe(3)O(4)@Al(2)O(3) NPs was employed to extract both analytes in 5 ml of aqueous solution. After 5 min extraction, magnetic NPs were isolated from sample solution by employing an external magnet. Followed by rinsing the NPs with 5 microl of 20 mM Na(4)P(2)O(7) solution for 5 min, the extract was directly analyzed using the derivatization-free CE-electrochemiluminescence (CE-ECL) method. With a sample-to-extract volume ratio of 1000, the enrichment factors for GLY and AMPA were 460 and 64, respectively. The limits of detection (LODs) were 0.3 and 30 ng ml(-1) for GLY and AMPA in water, respectively. The developed method was applied to the analysis of GLY in guava fruit. The LOD of GLY in guava was 0.01 microg g(-1). Total analysis time including sample pretreatment, SPE and CE-ECL was less than 1h.

Rapid and direct determination of glyphosate and aminomethylphosphonic acid in water using anion-exchange chromatography with coulometric detection

A simple, rapid, and low-cost coulometric method for direct detection of glyphosate and aminomethylphosphonic acid (AMPA) in water samples using anion-exchange chromatography and coulometric detection with copper electrode is presented. Under optimized conditions, the limits of detection (LODs) (S/N=3) were 0.038microgml(-1) for glyphosate and 0.24microgml(-1) for AMPA, without any preconcentration method. The calibration curves were linear and presented an excellent correlation coefficient. The method was successfully applied to the determination of glyphosate and AMPA in water samples without any kind of extraction, clean-up, or preconcentration step. No interferent was found in the water, like this, the recovery was, practically, 100%.