Integrated pulsed amperometric detection of glufosinate, bialaphos and glyphosate at gold electrodes in anion-exchange chromatography

Electrochemical biosensing based comparative study of monoclonal antibodies against SARS-CoV-2 nucleocapsid protein

In this study, we are reporting an electrochemical biosensor for the determination of three different clones of monoclonal antibodies (mAbs) against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recombinant nucleocapsid protein (rN). The nucleocapsid protein was chosen as a system component identifying and discriminating antibodies that occur after virus infection instead of S protein used in serological tests to measure antibodies raised after vaccination and infection. The sensing platform was based on a screen-printed carbon electrode (SPCE) covered with gold nanoparticles (AuNP) and subsequently modified with a self-assembled monolayer (SAM) to ensure the covalent immobilization of the rN. The interaction between the protein and three clones of mAbs against SARS-CoV-2 rN with clone numbers 4G6, 7F10, and 1A6, were electrochemically registered in the range of concentrations. Three techniques, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and pulse amperometric detection (PAD) were used for the detection. A gradual change in the responses with an increase in mAbs concentration for all techniques was observed. To assess the performance of the developed electrochemical biosensor, 'complexation constant' (KC), limit of detection (LOD), and limit of quantification (LOQ) were calculated for all assessed clones of mAbs and all used techniques. Our results indicated that DPV possessing higher fitting accuracy illustrated more significant differences in KC constants and LOD/LOQ values. According to the DPV results, 7F10 clone was characterized with the highest KC value of 1.47 ± 0.07 μg/mL while the lowest LOD and LOQ values belonged to the 4G6 clone and equaled 0.08 ± 0.01 and 0.25 ± 0.01 μg/mL, respectively. Overall, these results demonstrate the potential of electrochemical techniques for the detection and distinguishing of different clones of mAbs against SARS-CoV-2 nucleocapsid protein.

Simultaneous determination of three strong polarity herbicides in tea by ion chromatography-triple quadrupole mass spectrometry

Due to lack of chromogenic groups and fluorescence groups, high boiling point, high polarity, low volatility, and small molecular weight of glyphosate, glufosinate and bentazone, the detection of three analyses were limited in all kinds of food. Herein, a method for the simultaneous determination of glyphosate, glufosinate and bentazone in tea by ion chromatography tandem triple quadrupole mass spectrometry (IC-MS) was developed, which is without organic solvent and complex derivatization. The recoveries of three compounds in different teas (black tea, green tea, white tea) ranged from 80.40 % to 107.00 %, and the intraday precision (n = 6) ranged from 0.57 % to 9.90 %, the daytime precision ranged from 1.00 % to 5.30 %, the quantitative limit (LOQ) ranged from 0.36 to 1.30 µg/L, and the detection limit (LOD) ranged from 0.11 to 0.39 µg/L. Furthermore, the detection limit and quantitative limit of glyphosate, glufosinate and bentazone by this method are lower than other methods in real samples. Meanwhile, the established method was successfully applied to determine the terminal residues of the three analytes in twelve tea samples from commercial market. Therefore, this method can provide reliable technical support for the study of residue status in vegetables and fruits.

Applications of ion chromatography in urine analysis: A review

Ion chromatography (IC) plays a crucial role in urine analysis for diverse medical diagnoses. This paper reviews a comprehensive investigation into urine pretreatment techniques, as well as the design and development of IC systems for the measurement of various chemicals. Prior to analysis, urine samples commonly undergo pretreatment procedures such as dilution, filtration, purification, and concentration. These steps effectively eliminate interfering factors and facilitate the accurate and sensitive analysis of ultra-trace components. To separate and quantify different chemical elements or ions present in urine, a range of homemade or commercially available columns coupled with various detectors were employed. This study focuses on the analysis of chemicals such as heavy metals, halogens, pesticides, drugs, and other essential or toxic substances by IC methods.

Magnetic micromixing for highly sensitive detection of glyphosate in tap water by colorimetric immunosensor

Glyphosate is the most widely used herbicide in the world and, in view of its toxicity, there is a quest for easy-to-use, but reliable methods to detect it in water. To address this issue, we realized a simple, rapid, and highly sensitive immunosensor based on gold coated magnetic nanoparticles (MNPs@Au) to detect glyphosate in tap water. Not only the gold shell provided a sensitive optical transduction of the biological signal - through the shift of the local surface plasmon resonance (LSPR) entailed by the nanoparticle aggregation -, but it also allowed us to use an effective photochemical immobilization technique to tether oriented antibodies straight on the nanoparticles surface. While such a feature led to aggregates in which the nanoparticles were at close proximity each other, the magnetic properties of the core offered us an efficient tool to steer the nanoparticles by a rotating magnetic field. As a result, the nanoparticle aggregation in presence of the target could take place at higher rate (enhanced diffusion) with significant improvement in sensitivity. As a matter of fact, the combination of plasmonic and magnetic properties within the same nanoparticles allowed us to realize a colorimetric biosensor with a limit of detection (LOD) of 20 ng∙L^-1.

A Gold Nanoparticle-Based Molecular Self-Assembled Colorimetric Chemosensor Array for Monitoring Multiple Organic Oxyanions

Determination of oxyanions is of paramount importance because of the essential role they play in metabolic processes involved in various aquatic environmental problems. In this investigation, a novel chemical sensor array has been developed by using gold nanoparticles modified with different chain lengths of aminothiols (AET-AuNPs) as sensing elements. The proposed sensor array provides a fingerprint-like response pattern originating from cross-reactive binding events and capable of targeting various anions, including the herbicide glyphosate. In addition, chemometric techniques, linear discrimination analysis (LDA) and the support vector machine (SVM) algorithm were employed for analyte classification and regression/prediction. The obtained sensor array demonstrates a remarkable ability to determine multiple oxyanions in both qualitative and quantitative analysis. The described methodology could be used as a simple, sensitive and fast routine analysis for oxyanions in both laboratory and field settings.

Determination of Glufosinate-P-Ammonium in Soil Using Precolumn Derivation and Reversed-Phase High-Performance Liquid Chromatography

This study developed an analytical method to quantify glufosinate-P-ammonium (GLUF-P) in farmland soil using a reversed-phase high-performance liquid chromatography (HPLC) system with a fluorescence detector after derivatization. GLUF-P in farmland soil was extracted with a mixed alkaline solution and was further derivatized with 9-fluorenyl methyl chloroformate (FMOC) at 25 °C for 1 h. The derivatives were separated with an ACE-C18 column, gradient eluted with a mobile phase A of acetonitrile and a mobile phase B of 0.2% phosphoric acid solution, and finally determined by high-performance liquid chromatography (HPLC) with fluorescence detection at an excitation wavelength of 254 nm and an emission wavelength of 279.8 nm. The limits of detection (LODs) in the four types of soil ranged from 0.004 to 0.015 mg/kg, and the limits of quantification (LOQs) ranged from 0.0125 to 0.05 mg/kg. The mean recoveries of GLUF-P ranged from 94% to 119.8%, and the relative standard deviations (RSDs) varied between 2.8% and 9.0% when the spiked concentrations of GLUF-P were 0.1 mg/kg and 1.0 mg/kg, respectively. The coefficients of regression for the linearity equation were more than 0.99. The proposed method had high sensitivity and could be used for the determination of GLUF-P residues in farmland soil.

Towards electrochemical surface plasmon resonance sensor based on the molecularly imprinted polypyrrole for glyphosate sensing

In this research the molecular imprinting technology was applied for the formation of glyphosate-sensitive layer. The glyphosate imprinted conducting polymer polypyrrole (MIPpy) was deposited on a gold chip/electrode and used as an electrochemical surface plasmon resonance (ESPR) sensor. The results described in this study disclose some restrictions and challenges, which arise during the development of glyphosate ESPR sensor based on the molecularly imprinted polymer development stage. It was demonstrated, that glyphosate could significantly affect the electrochemical deposition process of molecularly imprinted polymer on the electrode. The results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and surface plasmon resonance (SPR) have demonstrated that glyphosate molecules tend to interact with bare gold electrode and thus hinder the polypyrrole deposition. As a possible solution, the formation of a self-assembled monolayer (SAM) of 11-(1H-Pyrrol-1-yl)undecane-1-thiol (PUT) before electrochemical deposition of MIPpy and NIPpy was applied. Dissociation constant (KD) and free energy of Gibbs (ΔG0) values of glyphosate on MIPpy and Ppy without glyphosate imprints (NIPpy) were calculated. For the interaction of glyphosate with MIPpy the KD was determined as 38.18 ± 2.33⋅10-5 and ΔG0 as -19.51 ± 0.15 kJ/mol.

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.

Electrochemical Microsensor for Microfluidic Glyphosate Monitoring in Water Using MIP-Based Concentrators

Glyphosate (GLY) is a broad-spectrum herbicide and is the most used pesticide worldwide. This vast usage has raised strong interest in the ecotoxicological impacts and human risks, with contamination of water being a major concern. Decentralized analytical techniques for water monitoring are of high importance. In this work, we present a small, low-cost, and time-effective electrochemical, chip-based microfluidic device for direct electrochemical detection of GLY downstream of a molecularly imprinted polymer (MIP) concentrator. We studied the electrochemical behavior of GLY and its metabolite aminomethylphosphonic acid (AMPA) using cyclic voltammetry with noble metal electrodes in acidic, neutral, and basic media. A chronoamperometric sensor protocol was developed for sensitive and selective GLY measurements on gold electrodes. The optimized protocol was transferred to a chip-based microsensor platform for online and real-time detection of GLY in a microfluidic setup. The results in the range from 0 to 50 μM GLY in 0.5 M H2SO4 show high linearity and a sensitivity of 10.3 ± 0.6 μA mm-2 mM-1 for the chip-based microfluidic platform. Successful recovery of GLY concentrated from untreated tap water and its precise detection from low volumes demonstrates the advantages of our system.

An efficient and simple method using a graphite oxide electrochemical sensor for the determination of glyphosate in environmental samples

Excessive and indiscriminate use of the herbicide glyphosate (GLY) leaves the environment susceptible to its contamination. This work describes the development of a simple, inexpensive, and efficient electroanalytical method using graphite oxide paste electrode (GrO-PE) for the direct determination of GLY traces in groundwater samples, soybean extracts, and lettuce extracts. Under optimal experimental conditions, the developed sensor exhibited a linear response of the peak current intensity vs. the concentration, in the range of 1.8 × 10^-5 to 1.2 × 10^-3 mol L^-1 for GLY. The limits of detection and quantification are 1.7 × 10^-8 mol L^-1 and 5.6 × 10^-8 mol L^-1, respectively. The methodology developed here demonstrated a strong analytical performance, with high reproducibility, repeatability, and precision. Moreover, it successfully avoided interference from other substances, showing high selectivity. The GrO-PE sensor was effectively applied to determine GLY traces in real samples with recovery rates ranging from 98% to 102%. Results showed that the GrO-PE is effective and useful for GLY detection, with the advantage of not involving laborious modifications and complicated handling, making it a promising tool for environmental analysis.

Validation of a simple ion chromatography method for simultaneous determination of glyphosate, aminomethylphosphonic acid and ions of Public Health concern in water intended for human consumption

The herbicide glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) are generally studied in environmental samples in the investigation of contamination of soil, plants, water and food. Many analytical methods are based on liquid chromatography or high-performance liquid chromatography, with pre-column or post-column derivatization; in addition, the chromatograph can be coupled to mass spectrometers for detection and quantification. Gas chromatography and spectroscopic and electrochemical methods have also been used. In this work, a simple low-cost method is presented for the analysis of water intended for human consumption with the quantification not only of glyphosate and AMPA, but also of other ions of interest to public health (fluoride, chlorite, bromate, chloride, nitrite, nitrate, sulfate and phosphate). Based on ion chromatography with conductivity detection (chemical suppression of eluent conductivity), the key point in this method is the use of gradient elution with two eluents of different pH and ionic strength, not requiring derivatization. There is no interference from the other ions at higher concentrations. The detection limits obtained for glyphosate and AMPA were 15 μg L-1 and 80 μg L-1, respectively. As the method allows the analysis of a large number of samples, it has been successfully applied to monitoring the quality of tap water in 89 municipalities in the northeast region of the State of São Paulo, Brazil.

Engineered glyphosate oxidase coupled to spore-based chemiluminescence system for glyphosate detection

The extensive and intensive utilization of glyphosate (Glyp) caused public concerns on the potential risk of environment and health resulted from the chemical residues. Therefore, the development of a high-selective, low-cost and easy-operation Glyp detection methods is highly desired. Screening highly selective enzymes by directed evolution is important in practical applications. Herein, a glyphosate oxidase (GlypO) preferring substrate Glyp to produce H2O2 was obtained via directed evolution from glycine oxidase obtained from Bacillus cereus (BceGO). The catalytic efficiency, specificity constant, and affinity enhancement factor of GlypO toward Glyp were increased by 2.85 × 103-fold; 2.25 × 105-fold; and 9.64 × 104-fold, respectively, compared with those of BceGO. The catalytic efficiency toward glycine decreased by 78.60-fold. The spores of Bacillus subtilis (B. subtilis) effectively catalyzed luminol-H2O2 reaction to create excellent chemiluminescence (CL) signal because CotA-laccase exists on their surface. Based on these findings, a new CL biosensor via coupling to biological reaction system was presented for Glyp detection. The CL biosensor exhibited several advantages, such as eco-friendliness, low cost, high selectivity and sensitivity, and good practical application prospects for environmental pollution control.

Determination of glyphosate and glufosinate in corn using multi-walled carbon nanotubes followed by ultra high performance liquid chromatography coupled with tandem mass spectrometry

Glyphosate (Glyp) and glufosinate (Gluf) are widely used herbicides around the world, and their effects on human health and detection of levels have drawn increasing attention. The present study was to establish a method to determine the contents of Glyp and Gluf from corn using multi-walled carbon nanotubes (MWCNTs) followed by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). The corn samples were purified by MWCNTs, then the analytes reacted with 9-fluorenylmethylchloroformate (FMOCCl) of acetonitrile solution (20.0 g/L) at 50 °C water bath in a borate buffer solution (50.0 g/L, pH=9) to generate FMOC derivative products. After the derivatization, HSS T3 was used as the separation column, with acetonitrile and 0.05% ammonia as the mobile phase, and multiple reaction monitoring (MRM) mode with negative electrospray ionization (ESI-) was adopted. The validation parameters showed good verification results, with both of their quantitative limits (LOQ) as 0.005 mg/kg, recoveries between 90.3% and 95.4%, intra-day relative standard deviations (RSDs) in the ranges of 1.24% and 3.35%, and inter-day RSDs between 3.56% and 6.06%. The analytical method, developed in this study, has high accuracy and sensitivity, and is suitable for the simultaneous detection of Glyp and Gluf in corn.

Recent Development on the Electrochemical Detection of Selected Pesticides: A Focused Review

Pesticides are heavily used in agriculture to protect crops from diseases, insects, and weeds. However, only a fraction of the used pesticides reaches the target and the rest slips through the soil, causing the contamination of ground- and surface water resources. Given the emerging interest in the on-site detection of analytes that can replace traditional chromatographic techniques, alternative methods for pesticide measuring have recently encountered remarkable attention. This review gives a focused overview of the literature related to the electrochemical detection of selected pesticides. Here, we focus on the electrochemical detection of three important pesticides; glyphosate, lindane and bentazone using a variety of electrochemical detection techniques, electrode materials, electrolyte media, and sample matrix. The review summarizes the different electrochemical studies and provides an overview of the analytical performances reported such as; the limits of detection and linearity range. This article highlights the advancements in pesticide detection of the selected pesticides using electrochemical methods and point towards the challenges and needed efforts to achieve electrochemical detection suitable for on-site applications.

Direct electrochemical detection of glyphosate at carbon paste electrode and its determination in samples of milk, orange juice, and agricultural formulation

This paper describes a simple, inexpensive, highly sensitive, selective, and efficient electrochemical method to determine glyphosate (GLY) in samples of milk, orange juice, and agricultural formulation. The oxidation reaction on the electrode surface was electrochemically characterised by cyclic voltammetry (CV) and square wave voltammetry (SWV). The investigation of GLY at carbon paste electrode revealed a non-reversible oxidation peak at +0.95 V versus Ag/AgCl, which was used for electrochemical detection of GLY. The operating parameters (pH, frequency, step potential, and amplitude) were optimised in relation to the peak current intensity, and a calibration curve was set up in a concentration range of 4.40 × 10-8-2.80 × 10-6 mol L-1, with a detection limit of 2 × 10-9 mol L-1. After calibration curve was plotted, the developed procedure was applied to determine GLY in previously contaminated samples: milk and orange juice, and in a commercial formulation, obtaining recovery values between 98.31% and 103.75%. These results show that the proposed method can be used for GLY quantification in different samples with high sensitivity, specificity, stability, and reproducibility.

Adsorption behavior and mechanism of glufosinate onto goethite

The adsorption of glufosinate (GLU), a widely used herbicide similar to glyphosate (GLY), onto goethite was investigated as a function of the pH, ionic strength, background cations and anions, heavy metal ions and fulvic acids (FAs) by using batch adsorption experiments. In situ ATR-FTIR spectroscopy and density functional theory (DFT) calculations were carried out to characterize the molecular interactions between GLU and goethite surfaces. The macroscopic results indicated that an increasing pH exerted an adverse effect on GLU adsorption because of the electrostatic repulsion, and the adsorption was not sensitive to ionic strengths or background cation types, indicating that an inner-sphere surface complex was involved. GLU adsorption can be considerably depressed by PO4(3-), SO4(2-), and a high level of FA because of the competitive effect, while being enhanced by Cu(2+) with a maximum adsorption at approximately pH5 because of the metal ion bridging effect. Other examined divalent metal cations (Cd(2+), Zn(2+), and Pb(2+)) showed almost no effect on GLU adsorption, indicating weak interaction between them. ATR-FTIR spectra and the DFT calculations further proved that GLU was bonded to goethite surfaces through the formation of a monodentate mononuclear inner-sphere complex between the phosphinic moiety and surface Fe(III) centers under an acidic condition. The results showed that GLU had a similar adsorption mechanism to that of GLY onto goethite, but with a lower adsorption affinity, possibly exerting higher mobility and risk in soils.

Direct and sensitive determination of glyphosate and aminomethylphosphonic acid in environmental water samples by high performance liquid chromatography coupled to electrospray tandem mass spectrometry

A novel method based on high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) was developed for the sensitive determination of glyphosate and its major degradation product, AMPA in environmental water samples. The method involves the use of MS compatible mobile phases (0.1% formic acid in water and acetonitrile) for HPLC and direct analysis of water samples without sample derivatization. The method has been validated in different types of water matrices (drinking, surface and groundwater) by accuracy and precision studies with samples spiked at 0.1, 7.5 and 90 ppb. All mean accuracy values ranged from 85% to 112% for glyphosate and AMPA using both primary and secondary quantitative ion transitions (RSD ≤ 10%). Moreover, both primary and secondary ion transitions for glyphosate and AMPA can achieve the quantitation limits at 0.1 ppb. The linear dynamic range of the calibration curves were from 0.1 to 100 ppb for each analyte at each ion transitions with correlation coefficient higher than 0.997.

Carbon dots based turn-on fluorescent probes for the sensitive determination of glyphosate in environmental water samples

Schematic illustration of Cu²⁺ and glyphosate detection using the CDs.

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.

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.

Determination of glyphosate in foodstuff by one novel chemiluminescence-molecular imprinting sensor

A novel chemiluminescence (CL) sensor for the determination of glyphosate (GLY) was made up based on molecularly imprinted polymer (MIP). The molecularly imprinted microspheres (MIMs) with a small dimension which possess extremely high surface-to-volume ratio were synthesized using precipitation polymerization with GLY as template. And then the MIMs were modified on glass sheets, which were placed at the bottom of wells of microplate as the recognizer. Subsequently, a highly selective and high throughput chemiluminescence (CL)-molecular imprinting (MI) sensor for detection of GLY was achieved. Influencing factors were investigated and optimized in detail. The method can perform 96 independent measurements sequentially in 10 min and the limit of detection (LOD) for GLY was 0.046 μg mL(-1). The relative standard deviation (RSD) for 11 parallel measurements of GLY was 4.68%. The results show that CL-MI sensor can become a useful analytical technology for quick molecular recognition.

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 microg mL(-1) for glyphosate, 0.05 microg mL(-1) for AMPA and 0.03 microg 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.

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.

Glyphosate herbicide residue determination in samples of environmental importance using spectrophotometric method

A simple selective spectrophotometric method has been developed for the determination of glyphosate herbicide in environmental and biological samples. Glyphosate was reacted with carbon disulphide to form dithiocarbamic acid which was further followed for complex formation with copper in the presence of ammonia. The absorbance of the resulting yellow coloured copper dithiocarbamate complex was measured at 435 nm with molar absorptivity of 1.864 x 10(3) L mol(-1)cm(-1).The analytical parameters were optimized and Beer's law was obeyed in the range of 1.0-70 microg mL(-1). The composition ratio of the complex was glyphosate: copper (2:1) as established by Job's method with a formation constant of 1.06 x 10(5). Glyphosate was satisfactorily determined with limit of detection and quantification of 1.1 and 3.7 microg mL(-1), respectively. The investigated method was applied successfully to the environmental samples. Recovery values in soil, wheat grains and water samples were found to be 80.0+/-0.46 to 87.0+/-0.28%, 95.0+/-0.88 to 102.0+/-0.98% and 85.0+/-0.68 to 92.0+/-0.37%, respectively.

Glyphosate and glufosinate detection at electrogenerated NiAl-LDH thin films

An amperometric sensor based on Ni(1-x)Al(x)(OH)(2)NO(3x).nH(2)O layered double hydroxide (LDH) has been developed for the electrochemical analysis in one step of two herbicides: glyphosate (N-(phosphonomethyl)glycine, Glyp) and glufosinate ((DL-homoalanine-4-yl)-methylphosphinic acid, Gluf). NiAl-LDH was prepared by coprecipitation or by electrodeposition at the Pt electrode surface. Inorganic films were fully characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Adsorption isotherms of Glyp onto this inorganic lamellar material have been established. Electrocatalytic oxidation of Glyp and Gluf is possible at the Ni(3+) centres of the structure. The electrochemical responses of the NiAl-LDH modified electrode were obtained by cyclic voltammetry and chronoamperometry at 0.49V/SCE as a function of herbicide concentration in 0.1M NaOH solution. The electrocatalytic response showed a linear dependence on the Glyp concentration ranging between 0.01 and 0.9mM with a detection limit of 1muM and sensitivity 287mA/Mcm(2). The sensitivity found for Gluf was lower (178mA/Mcm(2)).

Electrochemical detection of glyphosate herbicide using horseradish peroxidase immobilized on sulfonated polymer matrix

This paper describes the use of horseradish peroxidase (HRP) based biosensor for novel detection of glyphosate herbicide. The biosensor was prepared by electrochemically depositing poly(2,5-dimethoxyaniline) (PDMA) doped with poly(4-styrenesulfonic acid) (PSS) onto the surface of a gold electrode followed by electrostatic attachment of the enzyme HRP onto the PDMA-PSS composite film. Fourier transform infrared (FTIR) and UV-Vis spectrometry inferred that HRP was not denatured during its immobilization on PDMA-PSS composite film. The biosensing principle was based on the determination of the cathodic responses of the immobilized HRP to H(2)O(2), before and after incubation in glyphosate standard solutions. Glyphosate inhibited the activity of HRP causing a decrease in its response to H(2)O(2). The determination of glyphosate was achieved in the range of 0.25-14.0 microg L(-1) with a detection limit of 1.70 microg L(-1). The apparent Michaelis-Menten constant (calculated for the HRP/PDMA-PSS biosensor in the presence and absence of glyphosate was found to be 7.73 microM and 7.95 microM respectively.

An alternative and fast method for determination of glyphosate and aminomethylphosphonic acid (AMPA) residues in soybean using liquid chromatography coupled with tandem mass spectrometry

A simple and specific method using reversed-phase liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) was investigated, which allowed the determination of residues of glyphosate and its metabolite, aminomethylphosphonic acid (AMPA), in soybean samples. An aqueous extraction with liquid-liquid partition followed by protein precipitation was performed before the LC/MS/MS determination. The quantitation of glyphosate and AMPA was performed in positive and negative ESI mode, respectively, using the multiple reaction monitoring (MRM) mode with three transitions for each analyte to enhance the specificity of the method and avoid false positives. The methodology reported in this work is capable of detecting residues of glyphosate and AMPA in soybean samples with limits of quantification of 0.30 and 0.34 mg kg(-1), respectively. This alternative method has throughput advantages such as simpler sample preparation and faster chromatographic analysis.

Amperometric nanobiosensor for quantitative determination of glyphosate and glufosinate residues in corn samples

This study presents a simple, sensitive, rapid, and low-cost amperometric method for direct and quantitative determination of glyphosate and glufosinate herbicides. Electrochemical synthesis and characterization of poly(2,5-dimethoxyaniline)-poly(4-styrenesulfonic acid) (PDMA-PSS) nanoparticles was achieved by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The nanobiosensor was constructed by immobilizing the enzyme horseradish peroxidase (HRP) electrostatically onto the surface of a rotating gold disk electrode modified with PDMA-PSS nanoparticles. The biosensing principle was based on determination of the sensor response to glyphosate and glufosinate by amperometric methods. Hydrogen peroxide (H2O2) was used to measure activity of the enzyme before injection of the herbicides into the electrolyte solution. The enzyme electrode was stable for a long period of time and was used for over 60 measurements. Glyphosate and glufosinate analyses were realized on spiked corn samples within a concentration range of 2.0-78.0 μg L-1, corroborating that the nanobiosensor is sensitive enough to detect herbicides in these matrices. Based on a 20-μL sample injection volume, the detection limits were 0.1 μg L-1 (10-10 M) for both glyphosate and glufosinate without sample clean-up or preconcentration.

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%.

Glyphosate and AMPA analysis in sewage sludge by LC-ESI-MS/MS after FMOC derivatization on strong anion-exchange resin as solid support

An innovative analytical method has been developed for the determination of glyphosate and aminomethylphosphonic acid (AMPA), its major metabolite, in sewage sludge. This method involved an alkaline extraction from sludge and purification on a strong anion-exchange resin. While the analytes remained fixed by ionic interactions, an "on-solid support" derivatization by FMOC-Cl was carried out. This versatile approach allowed a 10 min reaction and simple elimination of the excess of reagent. The resulting derivatives remained retained by ionic and hydrophobic interactions with the resin until being eluted by a mixed NaCl water/acetonitrile, 70/30, v/v, solution. After an appropriate dilution and adjustment of the pH, the sample was concentrated on an Oasis HLB solid-phase cartridge. For quality analysis of traces in complex matrixes, LC-ESI-MS/MS in the multiple reaction monitoring positive mode was used fulfilling the European Union requirements (Decision 2002/657/CE). To overcome the matrix effects, stable isotopically labeled standards were added to the sludge extracts as internal standards and were thus derivatized during the procedure in parallel to the analytes. Mean recovery values were 70% +/- 7% for glyphosate and 63% +/- 3% for AMPA. Limits of detection (20 and 30 ppb dw) and limits of quantification (35 and 50 ppb dw) for glyphosate and AMPA, respectively, were sufficient to monitor samples taken from Ile-de-France wastewater treatment plants where contamination currently reached 0.1-3 ppm and 2-35 ppm dw for glyphosate and AMPA, respectively.

Direct determination of glyphosate using hydrophilic interaction chromatography with coulometric detection at copper microelectrode

A simple, rapid, and low-cost coulometric method for direct detection of glyphosate using hydrophilic interaction chromatography is presented. The principle of detection is based on the enhancement of the anodic current of copper microelectrode in the presence of complexing agents, such as glyphosate, with the formation of a soluble Cu(II) complex. Under optimized conditions, the limit of detection (S/R=3) for glyphosate was 0.1 mg L(-1) (0.59 microM) without any preconcentration method. The calibration curve has been found linear in all concentration range tested (from limit of detection to 34 mg L(-1)) with an excellent correlation coefficient (0.9999). The present method was successfully applied for the determination of glyphosate in fruit juices without any kind of extraction, clean-up, or preconcentration step, with recoveries of 92 and 90% for apple and grape juice, respectively.

Ion chromatography/inductively coupled plasma mass spectrometry for simultaneous determination of glyphosate, glufosinate, fosamine and ethephon at nanogram levels in water

This paper describes the first approach that simultaneously quantifies four polar, water-soluble organophosphorus herbicides, i.e., glyphosate, glufosinate, fosamine and ethephon, at nanogram levels in environmental waters. The target herbicides were separated completely by ion chromatography (IC) on a polymer anion-exchange column, Dionex IonPac AS16 (4.0 mm x 250 mm), with 30 mM citric acid flowing at 0.70 mL min(-1) as the eluent. On-line inductively coupled plasma mass spectrometry (ICP-MS) using a quadrupole mass spectrometer was employed as a sensitive and selective detector of the effluents. Various parameters affecting the separation and detection were systematically examined and optimized. Detection limits of the herbicides achieved with the proposed IC/ICP-MS method were 1.1-1.4 microg L(-1) (as compound) based on a 500-microL sample injection. Matrix anions, metal ions, phosphate, polyphosphates, non-polar and other polar organophosphorus pesticides showed no interference. The developed method was validated using reservoir water, treated water and NEWater samples spiked at the level of 10-25 microg L(-1) with satisfactory recoveries (95-109%). It is applicable to the simultaneous determination of microg L(-1) concentrations of the herbicides in polluted water.

Determination of glyphosate and phosphate in water by ion chromatography--inductively coupled plasma mass spectrometry detection

Quantitative determination of trace glyphosate and phosphate in waters was achieved by coupling ion chromatography (IC) separation with inductively coupled plasma mass spectrometry (ICP-MS) detection. The separation of glyphosate and phosphate on a polymer anion-exchange column (Dionex IonPac AS16, 4.0 mm x 250 mm) was obtained by eluting them with 20 mM citric acid at 0.50 mL min(-1), and the analytes were detected directly and selectively by ICP-MS at m/z = 31. Parameters affecting their chromatographic behaviors and ICP-MS characteristics were systematically examined. Based on a 500-microL sample injection volume, the detection limits were 0.7 microgL(-1) for both glyphosate and phosphate, and the calibrations were linear up to 400 microgL(-1). Polyphosphates, aminomethylphosphonic acid (the major metabolite of glyphosate), non-polar and other polar phosphorus-containing pesticides showed different chromatographic behaviors from the analytes of interest and therefore did not interference. The determination was also interference free from the matrix anions (nitrate, nitrite, sulphate, chloride, etc.) and metallic ions. The analysis of certified reference material, drinking water, reservoir water and Newater yielded satisfactory results with spiked recoveries of 97.1-107.0% and relative standard deviations of < or = 7.4% (n = 3). Compared to other reported methods for glyphosate and phosphate, the developed IC-ICP-MS method is sensitive and simple, and does not require any chemical derivatization, sample preconcentration and mobile phase conductivity suppression.

Glyphosate immunosensor. Application for water and soil analysis

A fully automated immunosensor for the herbicide glyphosate has been developed on the basis of the immunocomplex capture assay protocol. The sensor carries out on-line analyte derivatization prior to the assay and uses a selective anti-glyphosate serum, a glyphosate peroxidase enzyme tracer, and fluorescent detection. Under optimal conditions, the detection limit achieved is 0.021 microg/L with an analysis rate of 25 min per assay, autonomy of more than 48 h, and sensor reusability >500 analytical cycles. The immunosensor is able to discriminate structurally related molecules, such as aminomethylphosphonic acid, the main metabolite of glyphosate, and other related herbicides, such as glufosinate and glyphosine. Interferences from naturally occurring species (anions, cations, and humic substances) and their elimination were also studied. The immunosensor has been successfully applied to water and soil sample analysis, with good recoveries at levels lower than 1 microg/L. Results obtained with the immunosensor correlate well with data from a magnetic particle ELISA and LC/LC/MS chromatographic method.

A pulsed potential waveform displaying enhanced detection capabilities towards sulfur-containing compounds at a gold working electrode

Pulsed electrochemical detection of sulfur-containing compounds was successfully investigated by applying a four-step potential waveform at a gold working electrode. This potential waveform called APAD, which stands for activated pulsed amperometric detection, is composed of an activation potential step added to a conventional three-step potential waveform. A key advantage of the APAD at the Au electrode is the ability to enhance sensitivity through the use of a short potential pulse (E(ACT) = +750 mV versus Ag/AgCl and tACT approximately 90 ms) during which the formation of redox active species (presumably OH*) are able to efficiently oxidize organosulfur compounds. The APAD waveform parameters were optimized to maximize the signal-to-noise ratio (S/N) and successfully applied for the sensitive detection of lipoic acid, biotin, iminobiotin, methionine, cystine, cysteine, homocysteine, homocystine, N-acetylcysteine and glutathione, following their separations by high-performance anion-exchange chromatography (HPAEC) using alkaline mobile phases. The detection limits (S/N = 3, 10 microL injected) ranged from 0.3 for cysteine (400 pg) to 0.02 micromol/L for biotin (50 pg) and methionine (30 pg). The response of sulfur-, amine- and alcohol-based compounds was compared by using four selected pulsed potential waveforms. It was found that the APAD exhibits excellent sensitivity for thiocompounds outperforming all other pulsed potential waveforms. Ratios of the peak areas for APAD and the six-step potential integrated waveform increased from 3.2 +/- 0.4 to 13.5 +/- 0.6 for lipoic acid and biotin, respectively.