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

Picomolar detection limits for glyphosate by two-dimensional column-coupled isotachophoresis/capillary zone electrophoresis-mass spectrometry

Capillary electrophoresis-mass spectrometry often lacks sufficient limits of detection for trace substances in the environment due to its low loadability. To overcome this problem, we conducted a feasibility study for column-coupling isotachophoresis to capillary electrophoresis-mass spectrometry. The first dimension isotachophoresis preconcentrated the analytes. The column-coupling of both dimensions was achieved by a hybrid capillary microfluidic chip setup. Reliable analyte transfer by voltage switching was enabled by an in-chip capacitively coupled contactless conductivity detector placed around the channel of the common section between two T-shaped crossings in the chip connecting both dimensions. This eliminated the need to calculate the moment of analyte transfer. A commercial capillary electrophoresis-mass spectrometry instrument with easily installable adaptations operated the setup. Prior to coupling isotachophoresis with capillary zone electrophoresis-mass spectrometry, both dimensions were optimized individually by simulations and verified experimentally. Both dimensions were able to stack/separate all degradation products of glyphosate, the most important herbicide applied worldwide. The first dimension isotachophoresis also removed phosphate, which is a critical matrix component in many environmental samples. Enrichment and separation of glyphosate and its main degradation product aminomethylphosphonic acid by the 2D setup provided an excellent limit of detection of 150 pM (25 ng/L) for glyphosate. This article is protected by copyright. All rights reserved.

Determination of Glyphosate, Glufosinate, and Their Major Metabolites in Tea Infusions by Dual-Channel Capillary Electrophoresis following Solid-Phase Extraction

In this study, two analytical procedures were developed and validated using dual-channel capillary electrophoresis-coupled contactless conductivity detection (CE-C4D) followed by solid-phase extraction (SPE) for simultaneous determination of glyphosate (GLYP), glufosinate (GLUF), and their two major metabolites, aminomethylphosphonic acid (AMPA) and 3-(methylphosphinico) propionic acid (MPPA), respectively, in a popular beverage such as tea infusions. GLYP, GLUF, and AMPA were analyzed in the first channel using background electrolyte (BGE) of 1 mM histidine (His) adjusted to pH 2.75 by acetic acid (Ace). In contrast, MPPA was quantified in the second channel with a BGE of 30 mM His adjusted to pH 6.7 by 3-(N-morpholino) propanesulfonic acid (MOPS) and 10 µM of cetyltrimethylammonium bromide (CTAB). In addition, the samples of tea infusions were treated using SPE with 10 mL of 0.5 mM HCl in methanol as eluent. At the optimized conditions, the method detection limit (MDL) of GLYP, GLUF, AMPA, and MPPA is 0.80, 1.56, 0.56, and 0.54 μg/l, respectively. The methods were then applied to analyze four target compounds in 16 samples of tea infusions. GLYP was found in two infusion samples of oolong tea with concentrations ranging from 5.34 to 10.74 µg/L, and GLUF was recognized in three samples of green tea infusion in the range of 45.1-53.9 µg/L.

Capillary and microchip electrophoresis with contactless conductivity detection for analysis of foodstuffs and beverages

The paper provides a comprehensive survey of the use of capillary and microchip electrophoresis in combination with contactless conductivity detection (C⁴D) for the analysis of drinking water, beverages and foodstuffs. The introduction sets forth the fundamentals of conductivity detection anddescribes an axialC⁴Dversion. There is also a detailed discussion of the determination of inorganic ions, organic acids, fatty acids, amino acids, amines, carbohydrates, foreign substances and poisons from the standpoint of separation conditions, sample treatment and detection limits. Special attention is paid to the analysis of foodstuffs at microchips with emphasis on the employed material and connection of the microchip with the C⁴D. The review attempts to draw attention to modern trends, such as dual-opposite injection, field-enhanced sample injection, electromembrane extraction and on-line combination of microdialysis with CE. CE/C⁴D is characterised by high universality, high speed of analysis, simple sample preparation, small consumption of sample and other chemicals.

Challenges in the design of electrochemical sensor for glyphosate-based on new materials and biological recognition

Glyphosate (GLY) is the main ingredient in the weed killer Roundup and the most widely used pesticide in the world. Studies of the harmful effects of GLY on human health began to become more wide-ranging after 2015. GLY is listed by the International Agency for Research on Cancer (IARC) as a carcinogenic hazard to humans. Moreover, GLY has the property to complex with transition metals and are stable for long periods, being considered a high-risk element for different matrices, such as environmental (soil and water) and food (usually genetically modified crops). Since that, it was noticed an increment in the development of new analytical methods for its determination in different matrices like food, environmental and biological fluids. Noteworthy, the application of electrochemical techniques for downstream detection sparked interest due to the ability to minimize or eliminate the use of polluting chemicals, using simple and affordable equipment. This work aims to review the contribution of the electroanalytical methods for the determination of GLY in different food and environmental matrices. Parameters such as the electrochemical transduction techniques based on the electrical measurement signals, receptor materials for electrodes preparation, and the detection mechanisms are described in this review. The literature review shows that the electrochemical sensors are powerful detection system that can be improved by their design and by their portability to fulfil the needs of the GLY determination in laboratory benches, or even in situ analysis.

Capillary electrophoresis-mass spectrometry for the direct analysis of glyphosate: method development and application to beer beverages and environmental studies

In this study, we developed and validated a CE-TOF-MS method for the quantification of glyphosate (N-(phosphonomethyl)glycine) and its major degradation product aminomethylphosphonic acid (AMPA) in different samples including beer, media from toxicological analysis with Daphnia magna, and sorption experiments. Using a background electrolyte (BGE) of very low pH, where glyphosate is still negatively charged but many matrix components become neutral or protonated, a very high separation selectivity was reached. The presence of inorganic salts in the sample was advantageous with regard to preconcentration via transient isotachophoresis. The advantages of our new method are the following: no derivatization is needed, high separation selectivity and thus matrix tolerance, speed of analysis, limits of detection suitable for many applications in food and environmental science, negligible disturbance by metal chelation. LODs for glyphosate were < 5 μg/L for both aqueous and beer samples, the linear range in aqueous samples was 5-3000 μg/L, for beer samples 10-3000 μg/L. For AMPA, LODs were 3.3 and 30.6 μg/L, and the linear range 10-3000 μg/L and 50-3000 μg/L, for aqueous and beer samples, respectively. Recoveries in beer samples for glyphosate were 94.3-110.7% and for AMPA 80.2-100.4%. We analyzed 12 German and 2 Danish beer samples. Quantification of glyphosate and AMPA was possible using isotopically labeled standards without enrichment, purification, or dilution, only degassing and filtration were required for sample preparation. Finally, we demonstrate the applicability of the method for other strong acids, relevant in food and environmental sciences such as N-acetyl glyphosate, N-acetyl AMPA (present in some glyphosate resistant crop), trifluoroacetic acid, 2-methyl-4-chlorophenoxyacetic acid, glufosinate and its degradation product 3-(methylphosphinico)propionic acid, oxamic acid, and others.

Glyphosate analysis using sensors and electromigration separation techniques as alternatives to gas or liquid chromatography

Since its introduction in 1974, the herbicide glyphosate has experienced a tremendous increase in use, with about one million tons used annually today. This review focuses on sensors and electromigration separation techniques as alternatives to chromatographic methods for the analysis of glyphosate and its metabolite aminomethyl phosphonic acid. Even with the large number of studies published, glyphosate analysis remains challenging. With its polar and depending on pH even ionic functional groups lacking a chromophore, it is difficult to analyze with chromatographic techniques. Its analysis is mostly achieved after derivatization. Its purification from food and environmental samples inevitably results incoextraction of ionic matrix components, with a further impact on analysis derivatization. Its purification from food and environmental samples inevitably results in coextraction of ionic matrix components, with a further impact on analysis and also derivatization reactions. Its ability to form chelates with metal cations is another obstacle for precise quantification. Lastly, the low limits of detection required by legislation have to be met. These challenges preclude glyphosate from being analyzed together with many other pesticides in common multiresidue (chromatographic) methods. For better monitoring of glyphosate in environmental and food samples, further fast and robust methods are required. In this review, analytical methods are summarized and discussed from the perspective of biosensors and various formats of electromigration separation techniques, including modes such as capillary electrophoresis and micellar electrokinetic chromatography, combined with various detection techniques. These methods are critically discussed with regard to matrix tolerance, limits of detection reached, and selectivity.

Simultaneous electromembrane extraction of cationic and anionic herbicides across hollow polymer inclusion membranes with a bubbleless electrode

A new electric-field driven extraction approach based on the integration of a bubbleless electrode into the electromembrane extraction (EME) across hollow polymer inclusion membranes (HPIMs) was demonstrated for the first time. The bubbleless electrode was prepared based on an in-situ synthesised polyacrylamide within a fused silica capillary. The electrode functions as a salt bridge, which conducts the electrical current between the acceptor phase in the lumen of the HPIM and the acceptor solution in the reservoir connected to a high voltage supply through a platinum electrode. Two types of HPIMs were employed, which consisted of desired proportions of cellulose acetate as base polymer, tris(2-ethylhexyl)phosphate as plasticizer, and di-(2-ethylhexyl)phosphoric acid as anionic carrier or Aliquat 336 as cationic carrier, respectively. The EME strategy was evaluated for the simultaneous determination of cationic quaternary ammonium and anionic chlorophenoxy acetic acid herbicides present in the river water, respectively. The analysis was carried out using capillary electrophoresis coupled with UV and contactless conductivity detection. Under the optimised conditions, enrichment factors in the range of 152-185-fold were obtained from 4mL of river water sample with a 20min extraction time and an applied voltage of 3000V. The proposed method provided good linearity with correlation coefficients ranging from 0.9982 to 0.9997 over a concentration range of 1-1000μg/L. The detection limits of the method for the herbicides were in the range of 0.3-0.4μg/L, with relative standard deviations of between 4.8% and 8.5%. The relative recoveries obtained when analysing the spiked river water ranged from 99.1% to 100%. A comparison was also made between the newly developed approach with the conventional EME setup by placing the platinum electrode directly in the lumen of the HPIMs.

Recent Advances in the Determination of Pesticides in Environmental Samples by Capillary Electrophoresis

Nowadays, owing to the increasing population and the attempts to satisfy its needs, pesticides are widely applied to control the quantity and quality of agricultural products. However, the presence of pesticide residues and their metabolites in environmental samples is hazardous to the health of humans and all other living organisms. Thus, monitoring these compounds is extremely important to ensure that only permitted levels of pesticide are consumed. To this end, fast, reliable, and environmentally friendly methods that can accurately analyze dilute, complex samples containing both parent substances and their metabolites are required. Focusing primarily on research published since 2010, this review summarizes the use of various sample pretreatment techniques to extract pesticides from various matrices, combined with on-line preconcentration strategies for sensitivity improvement, and subsequent capillary electrophoresis analysis.

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.

Electro-driven extraction across a polymer inclusion membrane in a flow-through cell

A flow-through arrangement for electrodriven extraction across a polymer inclusion membrane was developed. Sample introduction into the donor chamber was continuous, while the acceptor solution was stagnant. By adjustment of the total volume of the donor solution pumped through the cell the best compromise between enrichment factor and extraction time can be set. The enriched extract was analyzed by capillary electrophoresis with contactless conductivity detection. Membranes of 20μm thickness were employed which consisted of 60% cellulose triacetate as base polymer, 20% o-nitrophenyl octyl ether as plasticizer, and 20% Aliquat 336. By passing through 10mL of sample at a flow rate of 1mL/min the model analytes glyphosate (a common herbicide) and its major metabolite aminomethylphosphonic acid could be transported from the aqueous donor solution to the aqueous acceptor solution with efficiencies >87% in 10min at an applied voltage of 1500V. Enrichment factors of 87 and 95 and limits of detection down to 43 and 64pg/mL were obtained for glyphosate and aminomethylphosphonic acid, respectively. The intra- and interday reproducibilities for the extraction of the two compounds from spiked river water were about 6 and 7% respectively when new membranes were used for each experiment. For consecutive extractions of batches of river water with a single piece of membrane a deterioration of recovery by about 16% (after 20 runs) was noted, an effect not observed with purely aqueous standards.

Determination of glyphosate and AMPA on polyester-toner electrophoresis microchip with contactless conductivity detection

This paper reports a method for rapid, simple, direct, and reproducible determination of glyphosate and its major metabolite aminomethylphosphonic acid (AMPA). The platform described herein uses polyester-toner microchips incorporating capacitively coupled contactless conductivity detection and electrophoresis separation of the analytes. The polyester-toner microchip presented 150 μm-wide and 12 μm-deep microchannels, with injection and separation lengths of 10 and 40 mm long, respectively. The best results were obtained with 320 kHz frequency, 4.5 Vpp excitation voltage, 80 mmol/L CHES/Tris buffer at pH 8.8, injection in -1.0 kV for 7 s, and separation in -1.5 kV. RSD values related to the peak areas for glyphosate and AMPA were 1.5 and 3.3% and 10.1 and 8.6% for intra- and interchip assays, respectively. The detection limits were 45.1 and 70.5 μmol/L, respectively, without any attempt of preconcentration of the analytes. Finally, the method was applied to river water samples in which glyphosate and AMPA (1.0 mmol/L each) were added. The recovery results were 87.4 and 83.7% for glyphosate and AMPA, respectively. The recovery percentages and LOD values obtained here were similar to others reported in the literature.

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.

Recent progress for capillary electrophoresis with electrochemical detection

Capillary electrophoresis (CE) is an attractive technique in separation science because of its high separation performance, short analysis time and low cost. Electrochemical detection (EC) is a powerful tool for CE because of its high sensitivity. In this review, developments of CE-EC from 2008 to August, 2011 are reviewed. We choose papers of innovative and novel results to demonstrate the newest and most important progress in CE-EC.

Recent advances in applications of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D): an update

Capillary electrophoresis with a capacitively contactless conductivity detector (CE-C⁴D) is becoming a significant useful technique for the analysis of analytes in various fields such as pharmaceutical, biomedical, food and environmental. This review is an update describing the recent developments in the application of CE with a C⁴D detector.

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.

Electric field-driven extraction of lipophilic anions across a carrier-mediated polymer inclusion membrane

The use of a cationic carrier-mediated polymer inclusion membrane (PIM) for extraction and preconcentration of anionic model analytes driven by an electric field directly into an aqueous acceptor solution is demonstrated. The optimized membrane was 20 μm thick and consisted of 60% cellulose triacetate as base polymer, 20% o-nitrophenyl octyl ether as plasticizer, and 20% Aliquat 336 as cationic carrier in the perchlorate form. By applying voltages of up to 700 V across the membrane, the lipophilic model analytes propanesulfonate, octanesulfonate, and decanesulfonate could be transported from the aqueous donor solution to the aqueous acceptor solution with efficiences >90% within 5 to 20 min. A preconcentration factor of 26, defined by the volume ratio between donor and acceptor compartments of the current cell design, could be achieved. The utility of the method for analytical applications is demonstrated by extraction of the herbicide glyphosate and its breakdown product aminomethylphosphonic acid from spiked river water, followed by quantification with capillary electrophoresis using contactless conductivity detection. Limits of detection of 0.8 and 1.5 ng/mL were obtained for glyphosate and aminomethylphosphonic acid, respectively.