Core-Shell Nanocables Decorated with Carbon Spherical Shells and Silver Nanoparticles for Sensing Ethinylestradiol Hormone in Water Sources and Pills

The selective, rapid detection of low levels of hormones in drinking water and foodstuffs requires materials suitable for inexpensive sensing platforms. We report on core-shell Ag@C nanocables (NCs) decorated with carbon spherical shells (CSSs) and silver nanoparticles (AgNPs) by using a hydrothermal green approach. Sensors were fabricated with homogeneous, porous films on screen-printed electrodes, which comprised a 115 nm silver core covered by a 122 nm thick carbon layer and CSSs with 168 nm in diameter. NCs and CSSs were also decorated with 10-25 nm AgNPs. The NC/CSS/AgNP sensor was used to detect ethinylestradiol using square wave voltammetry in 0.1 M phosphate buffer (pH 7.0) over the 1.0-10.0 μM linear range with a detection limit of 0.76 μM. The sensor was then applied to detect ethinylestradiol in tap water samples and a contraceptive pill with recovery percentages between 93 and 101%. The high performance in terms of sensitivity and selectivity for hormones is attributed to the synergy between the carbon nanomaterials and AgNPs, which not only increased the sensor surface area and provided sites for electron exchange but also imparted an increased surface area.

Sustainable plant-wearable sensors for on-site, rapid decentralized detection of pesticides toward precision agriculture and food safety

The synergy between eco-friendly biopolymeric films and printed devices leads to the production of plant-wearable sensors for decentralized analysis of pesticides in precision agriculture and food safety. Herein, a simple method for fabrication of flexible, and sustainable sensors printed on cellulose acetate (CA) substrates has been demonstrated to detect carbendazim and paraquat in agricultural, water and food samples. The biodegradable CA substrates were made by casting method while the full electrochemical system of three electrodes was deposited by screen-printing technique (SPE) to produce plant-wearable sensors. Analytical performance was assessed by differential pulse (DPV) and square wave voltammetry (SWV) in a linear concentration range between 0.1 and 1.0 μM with detection limits of 54.9 and 19.8 nM for carbendazim and paraquat, respectively. The flexible and sustainable non-enzymatic plant-wearable sensor can detect carbendazim and paraquat on lettuce and tomato skins, and also water samples with no interference from other pesticides. The plant-wearable sensors had reproducible response being robust and stable against multiple flexions. Due to high sensitivity and selectivity, easy operation and rapid agrochemical detection, the plant-wearable sensors can be used to detect biomarkers in human biofluids and be used in on-site analysis of other hazardous chemical substances.

Optimized paper-based electrochemical sensors treated in acidic media to detect carbendazim on the skin of apple and cabbage

Wearable sensors such as those made with paper are needed for non-destructive routine analysis of pesticides on plants, fruits, and vegetables. Herein we report on electrochemical sensors made with screen-printed carbon electrodes on kraft and parchment papers to detect the fungicide carbendazim. A systematic optimization was performed to find that electrochemical sensors on kraft paper treated in an acidic medium led to the highest performance, with a detection limit of 0.06 µM for carbendazim. The enhanced sensitivity for this sensor was attributed to the porous nature of kraft paper, which allowed for a large electrode surface area, and to the carboxylic groups formed during electrochemical activation. As a proof-of-concept, the electrochemical sensor attached to the skin of apple and cabbage was used to detect carbendazim with the same performance as the gold standard method, thus demonstrating that the sensor can be used in the farm and on supermarket shelves.

Label-Free Electrochemical Immunosensor Made with Tree-like Gold Dendrites for Monitoring 25-Hydroxyvitamin D3 Metabolite

Flexible, fully printed immunosensors can meet the requirements of precision nutrition, but this demands optimized molecular architectures to reach the necessary sensitivity. Herein, we report on flexible and label-free immunosensor chips made with tree-like gold dendrites (AuDdrites) electrochemically formed by selective desorption of l-cysteine (L-cys) on (111) gold planes. Electrodeposition was used because it is scalable and cost-effective for a rapid, direct growth of Au hyperbranched dendritic structures. The 25-hydroxyvitamin D3 (25(OH)D3) metabolite was detected within 15 min with a limit of detection (LOD) of 0.03 ng mL^-1. This high performance was possible due to the careful optimization of the electroactive layer and working conditions for square wave voltammetry (SWV). Electrocrystallization was manipulated by controlling the deposition potential and the molar ratio between HAuCl₄ and L-cys. Metabolite detection was performed on human serum and saliva samples with adequate recovery between 97% and 100%. The immunosensors were stable and reproducible, unresponsive to interference from other molecules in human serum and saliva. They can be extended for use as wearable sensors with their mechanical flexibility and possible customization.

Photocatalysis of TiO2 Sensitized with Graphitic Carbon Nitride and Electrodeposited Aryl Diazonium on Screen-Printed Electrodes to Detect Prostate Specific Antigen under Visible Light

We report on a photoelectrochemical (PEC) device to detect prostatic-specific antigen (PSA) under visible LED light irradiation within the point-of-care (POC) paradigm. The device consists of a 3D printed miniaturized photoelectrochemical system and a disposable PEC immunosensor made with screen-printed carbon electrodes (SPCEs). The SPCEs were coated with nickel single atoms anchored on graphitic carbon nitride (Ni-gC₃N₄), titanium dioxide nanoparticles (TiO₂), and aryl diazonium salt prepared from p-aminobenzoic acid. The electrodeposited aryl diazonium on Ni-gC₃N₄/TiO₂ decreased the recombination of photogenerated charge carriers, leading to a 3.1-fold increase in the photocurrent compared to pure TiO₂. This functionalization strategy provides carboxylic groups to anchor antibodies via the carbodiimide reaction, which may be extended to any other type of immunosensor. Under optimal conditions, the PEC immunosensor was able to detect PSA from 10^-16 to 10^-8 g mL^-1 with a detection limit of 0.06 fg mL^-1. The device robustness was confirmed with reproducibility and stability tests. PSA could also be detected in human serum samples, which demonstrates the potential of the PEC immunosensor for clinical diagnosis.

Wearable sensors made with solution-blow spinning poly(lactic acid) for non-enzymatic pesticide detection in agriculture and food safety

On-site monitoring the presence of pesticides on crops and food samples is essential for precision and post-harvest agriculture, which demands nondestructive analytical methods for rapid, low-cost detection that is not achievable with gold standard methods. The synergy between eco-friendly substrates and printed devices may lead to wearable sensors for decentralized analysis of pesticides in precision agriculture. In this paper we report on a wearable non-enzymatic electrochemical sensor capable of detecting carbamate and bipyridinium pesticides on the surface of agricultural and food samples. The low-cost devices (<US$ 0.08 per unit) contained three-electrode systems deposited via screen-printing technology (SPE) on solution-blow spinning mats of poly (lactic acid) (PLA). The flexible PLA/SPE sensors can be used on flat, curved and irregular surfaces of leaves, vegetables and fruits. Detection was performed using differential pulse voltammetry and square wave voltammetry with detection limits of 43 and 57 nM for carbendazim and diquat, respectively. The wearable non-enzymatic sensor can discriminate and quantify carbendazim and diquat on apple and cabbage skins with no interference from other pesticides. The use of such wearable sensors may be extended to other agrochemicals, including with incorporation of active bio (sensing) layers for online monitoring of any type of agricultural products and foods.

Flexible and integrated dual carbon sensor for multiplexed detection of nonylphenol and paroxetine in tap water samples

Multiplex detection of emerging pollutants is essential to improve quality control of water treatment plants, which requires portable systems capable of real-time monitoring. In this paper we describe a flexible, dual electrochemical sensing device that detects nonylphenol and paroxetine in tap water samples. The platform contains two voltammetric sensors, with different working electrodes that were either pretreated or functionalized. Each working electrode was judiciously tailored to cover the concentration range of interest for nonylphenol and paroxetine, and square wave voltammetry was used for detection. An electrochemical pretreatment with sulfuric acid on the printed electrode enabled a selective detection of nonylphenol in 1.0-10 × 10^-6 mol L^-1 range with a limit of detection of 8.0 × 10^-7 mol L^-1. Paroxetine was detected in the same range with a limit of detection of 6.7 × 10^-7 mol L^-1 using the printed electrode coated with a layer of carbon spherical shells. Simultaneous detection of the two analytes was achieved in tap water samples within 1 min, with no fouling and no interference effects. The long-term monitoring capability of the dual sensor was demonstrated in phosphate buffer for 45 days. This performance is statistically equivalent to that of high-performance liquid chromatography (HPLC) for water analysis. The dual-sensor platform is generic and may be extended to other water pollutants and clinical biomarkers in real-time monitoring of the environment and health conditions. Silver pseudo-reference electrodes for paroxetine (REP) and nonylphenol (REN), working electrodes for paroxetine (WP) and nonylphenol (WN), and auxiliary electrode (AE). USP refers to the University of Sao Paulo. "Red" is reduced form and "Oxi" is oxidized form of analytes.

Biomimetic electrochemical sensors: New horizons and challenges in biosensing applications

The urge to meet the ever-growing needs of sensing technology has spurred research to look for new alternatives to traditional analytical methods. In this scenario, the glucometer is the flagship of commercial electrochemical sensing platforms, combining selectivity, reliability and portability. However, other types of enzyme-based biosensors seldom achieve the market, in spite of the large and increasing number of publications. The reasons behind their commercial limitations concern enzyme denaturation, and the high costs associated with procedures for their extraction and purification. In this sense, biomimetic materials that seek to imitate the desired properties of natural enzymes and biological systems have come out as an appealing path for robust and sensitive electrochemical biosensors. We herein portray the historical background of these biomimicking materials, covering from their beginnings until the most impactful applications in the field of electrochemical sensing platforms. Throughout the discussion, we present and critically appraise the major benefits and the most significant drawbacks offered by the bioinspired systems categorized as Nanozymes, Synzymes, Molecularly Imprinted Polymers (MIPs), Nanochannels, and Metal Complexes. Innovative strategies of fabrication and challenging applications are further reviewed and evaluated. In the end, we ponder over the prospects of this emerging field, assessing the most critical issues that shall be faced in the coming decade.

Functionalized polyacrylamide as an acetylcholinesterase-inspired biomimetic device for electrochemical sensing of organophosphorus pesticides

A plethora of publications has continuously reported electrochemical biosensors for detection of pesticides. However, those devices rarely accomplish commercial application due to technical issues associated with the lack of stability and high cost of the biological recognition element (enzyme). Alternatively, the biomimetic catalysts have arisen as a candidate for application in electrochemical biosensors to overcome the enzymatic drawbacks, combining low cost scalable materials with superior stability. Herein, for the first time, we propose a biomimetic biosensor for organophosphorus pesticide detection employing a functionalized polyacrylamide, polyhydroxamicalkanoate (PHA), which mimics the performance of the acetylcholinesterase (AChE) enzyme. The PHA bears functional groups inserted along its backbone chain working as active sites. Thereby, PHA was immobilized on screen printed electrodes (SPE) through a blend formation with poly(ethylene glycol) methyl ether (mPEG) to prevent its leaching out from the surface. Under optimum conditions, the biomimetic sensor was employed for the amperometric detection of paraoxon-ethyl, fenitrothion and chlorpyrifos ranging from 1.0 and 10.0μmolL^-1 with a limit of detection of 0.36μmolL^-1, 0.61μmol L^-1, and 0.83μmolL^-1, respectively. Typical AChE-based interfering species did not affect the PHA performance, which endorsed its superior behavior. The proposed biomimetic biosensor, denoted as SPE/PHA/mPEG, represents a significant advance in the field, offering a new path for low cost devices by means of an artificial enzyme, simple configuration and superior stability. Moreover, the biosensor performance can be further improved by modifying the electrode surface to enhance electronic transfer rate.

Polyhydroxamicalkanoate as a bioinspired acetylcholinesterase-based catalyst for acetylthiocholine hydrolysis and organophosphorus dephosphorylation: experimental studies and theoretical insights

A biomimetic polymer revealed a acetylcholinesterase-based performance.

Decoration of reduced graphene oxide with rhodium nanoparticles for the design of a sensitive electrochemical enzyme biosensor for 17β-estradiol

A novel nanocomposite material consisting of reduced graphene oxide/Rh nanoparticles was prepared by a one-pot reaction process. The strategy involved the simultaneous reduction of RhCl₃ and graphene oxide with NaBH₄ and the in situ deposition of the metal nanoparticles on the 2D carbon nanomaterial planar sheets. Glassy carbon electrode coated with this nanocomposite was employed as nanostructured support for the cross-linking of the enzyme laccase with glutaraldehyde to construct a voltammperometric biosensor for 17β-estradiol in the 0.9-11 pM range. The biosensor showed excellent analytical performance with high sensitivity of 25.7AµM^-1cm^-1, a very low detection limit of 0.54pM and high selectivity. The biosensor was applied to the rapid and successful determination of the hormone in spiked synthetic and real human urine samples.

Adsorption according to the Langmuir–Freundlich model is the detection mechanism of the antigen p53 for early diagnosis of cancer

The Langmuir–Freundlich model is used to explain the adsorption of the p53 biomarker onto an immunosensor for early detection of cancer.

A nanostructured label-free platform based on an ultrathin film for ultrasensitive detection of a secosteroid hormone

We report the electrocatalytic activity of perovskite-type LaNiO₃-nanoxide (LN-NO) on secosteroid hormone oxidation in alkaline solution.

4'-Aminochalcones as novel inhibitors of the chlorinating activity of myeloperoxidase

The excessive activation of neutrophils generates reactive oxygen species (ROS) and the secretion of primary granular enzymes, such as myeloperoxidase (MPO), which is implicated in numerous inflammatory diseases. The aim of this study was to evaluate chalcones as inhibitors of the chlorinating activity of MPO using in vitro and ex vivo assays. In addition to cytotoxic properties, the inhibition of respiratory burst, the scavenger capacity, and the oxidation potential were measured. 4'-Aminochalcone (1), 4'-amino-4- fluorochalcone (2), and 4'-amino-4-methylchalcone (3) exhibited potent inhibition of the chlorinating activity of MPO, as evaluated in a neutrophil system and a free cell system, to the following degree: (1) IC50 = 0.265 � 0.036 μmol L-1; (2) IC50 = 0.250 � 0.081 μmol L-1; and (3) IC50 = 0.250 � 0.012 μmol L-1. These values were similar to those for 5-fluorotryptamine (IC50 = 0.192 � 0.012 μmol L-1), a compound considered to be a potent MPO inhibitor. These aminochalcones were not toxic to neutrophils at concentrations below 100 μmol L- 1, as determined by the trypan blue exclusion assay. Compounds 1-3 presented a high oxidation potential (Epa1 ≉ 0.80 V), low scavenger capacity against DPPH• and HOCl, and low inhibition of respiratory burst. These data indicated that aminochalcones are potent inhibitors of MPO chlorinating activity, a new property for chalcone derivatives, given that they are neither antioxidant agents nor inhibitors of respiratory burst. In conclusion, the selected aminochalcones have potential as pharmacological agents for inflammatory diseases.

Photo-assisted electrochemical degradation of the commercial herbicide atrazine

This paper presents a degradation study of the pesticide atrazine using photo-assisted electrochemical methods at a dimensionally stable anode (DSA(®)) of nominal composition Ti/Ru(0.3)Ti(0.7)O(2) in a prototype reactor. The effects of current density, electrolyte flow-rate, as well as the use of different atrazine concentrations are reported. The results indicate that the energy consumption is substantially reduced for the combined photochemical and electrochemical processes when compared to the isolated systems. It is observed that complete atrazine removal is achieved at low current densities when using the combined method, thus reducing the energy required to operate the electrochemical system. The results also include the investigation of the phytotoxicity of the treated solutions.

Study of photo-assisted electrochemical degradation of carbaryl at dimensionally stable anodes (DSA)

This paper presents the results concerning the degradation of the pesticide carbaryl comparing two methods: electrochemical (EC) and photo-assisted electrochemical (PAEC). The experimental variables of applied current density, electrolyte flow-rate and initial carbaryl concentration were investigated. The results demonstrate that the electrochemical degradation of carbaryl was greatly enhanced when simultaneous UV light was applied. The greatest difference between the PAEC and EC method was apparent when lower current densities were applied. The extent of COD removal was much enhanced for the combined method, independent of the applied current density. It should be noted that the complete removal of carbaryl was achieved with out the need to add NaCl to the reaction mixture, avoiding the risk of chlorinated organic species formation.

Decolourisation of real textile waste using electrochemical techniques: effect of electrode composition

The present paper presents the study of the decolourisation of real textile effluent by constant current electrolysis in a flow-cell using a DSA type material. The effect of using different anode materials (Ti/Ru(0.3)Ti(0.7)O(2); Ti/Ir(0.3)Ti(0.7)O(2); Ti/Ru(X)Sn(1-X)O(2), where X=0.1, 0.2 or 0.3) on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm(-2)) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. In this case the greatest degree of colour removal is achieved when anode containing 90% SnO(2) is used. If the conductivity of the effluent is increased by adding NaCl (0.1 mol L(-1)) appreciable colour/TOC removal is observed. The efficiencies of colour and TOC removal are discussed in terms of the energy per order (E(EO)/kW h m(-3)order(-1)) and energy consumption (E(C)/kW h kg(-1)TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature.

Photo-assisted electrochemical oxidation of atrazine on a commercial Ti/Ru0.3Ti0.7O2 DSA electrode

This paper presents the study of the degradation of the pesticide atrazine, employing photoassisted electrochemical methods at a dimensionally stable anode of nominal composition Ti/Ru0.3Ti0.7O2. All experiments were performed in a flow cell, and the effects of current density, electrolyte flow rate, as well the use of different supporting electrolytes are reported. The results indicate that the energy per order (E(EO)/kW h m(-3) order(-1)) is substantially reduced when the photochemical and electrochemical techniques are combined. It is observed that complete atrazine removal is achieved at low current densities when the combined method is employed, thus reducing the energy required to operate the electrochemical system. The study of the electrolyte flow rate through the cell indicates that the photoassisted removal of atrazine is controlled by mass transfer. The degradation of commercial atrazine solutions is also presented, and the results show that the efficiency of atrazine removal is reduced compared with that of simulated solutions, due to the presence of the additional components present in the commercial formula.

Decolorisation of real textile waste using electrochemical techniques: effect of the chloride concentration

The present paper presents the study of the decolorisation of real textile effluent by constant current electrolysis in a flow-cell using a Ti/Ru(0.3)Ti(0.7)O(2) DSA type electrode. The effect of increasing the chloride ion concentration on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm(-2)) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. If the conductivity of the effluent is increased by adding 0.033 mol L(-1) Na(2)SO(4), little increase in the extent of colour/TOC removal is observed. However, when Na(2)SO(4) is substituted, stepwise, with NaCl (while maintaining the ionic strength constant) appreciable colour/TOC removal is observed. The study of the effect of increasing the current density demonstrates that total colour removal is possible at high currents. The efficiencies of colour and TOC removal are discussed in terms of the Energy per order (E(EO)/kWh m(-3)order(-1)) and Energy consumption (E(C)/kWh kg(-1)TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature.

Voltammetric detection of paraquat pesticide on a phthalocyanine-based pyrolitic graphite electrode

This work describes the application of an ordinary pyrolitic graphite electrode modified by metallophthalocyanine allied to square wave voltammetry for the study of the electrochemical behavior of the herbicide paraquat and the development of a method for its analytical determination in natural water samples. Preliminary experiments indicated that the best responses, considering the intensities of the current and voltammetric profile for the paraquat reduction process, were obtained when the electrode modified by cobalt phthalocyanine was employed, which had a better catalytic activity as a result of this modification compared with that for an unmodified electrode and electrodes modified by iron, manganese and the acid form of the phthalocyanines. Studies of the concentration of cobalt phthalocyanine and the adsorption time showed that 1.0x10(-4) mol L(-1) cobalt phthalocyanine with an adsorption time of 10 min was sufficient to obtain reliability and stability of modification for employment in the development of the electroanalytical procedure for paraquat determination in natural water samples. The variation in pH of a 0.10 mol L(-1) Britton-Robinson buffer solution and the square wave parameters indicated that the best conditions to reduce paraquat were pH 7.0, a frequency of 100 s(-1), a scan increment of 2 mV and a square wave amplitude of 50 mV. Under such conditions, the variation of paraquat concentrations from 5.00x10(-7) to 2.91x10(-5) mol L(-1) showed a linear relation, with detection and quantification limits of 26.53 and 88.23 microg L(-1); those values were lower than the maximum limits for drinking water permitted by the Brazilian Environmental Council (100 microg L(-1)), indicating that the method could be employed to analyze paraquat in drinking water samples.

Electrochemical oxidation of benzene on boron-doped diamond electrodes

This work presents an electrochemical investigation of the benzene oxidation process in aqueous solution on boron-doped diamond (BDD) electrodes. Additionally, in order to determine the main products generated during the oxidation process, electrolysis and high performance liquid chromatography experiments were carried out. The complete degradation of this compound was performed aiming to a further application in waste water treatment. The cyclic voltammetry studies indicate that benzene is irreversibly oxidized in acid medium (H2SO4 0.5 M) on the BDD electrode surface at 2.0 V versus Ag/AgCl in a diffusion controlled process. During the cycling, other products are generated, and a pair of peaks was observed that can be associated with the oxi-reduction of anyone of the following species: hydroquinone, benzoquinone, resorcinol or catechol. The electrolysis experiments were carried out at 2.4 and 2.5 V on the BDD electrode surface in a solution containing 1x10(-2) M of benzene (below the saturation concentration in aqueous solution), for 3 and 5 h, respectively. The main products measured were: hydroquinone, resorcinol, p-benzoquinone, catechol and phenol. The complete electrochemical benzene degradation was performed in the electrolysis experiments using a rotating BDD disc electrode (2.5 V for 5 h) and the main products detected were all measured at concentrations lower than 10(-5) M in this condition. The boron-doped diamond electrode had proved to be a valuable tool for the electrochemical degradation of the benzene, a very stable chemical compound.

Determination of triazine herbicides: development of an electroanalytical method utilizing a solid amalgam electrode that minimizes toxic waste residues, and a comparative study between voltammetric and chromatographic techniques

The use of a copper solid amalgam electrode (CuSAE) for the analytical determination of triazine herbicides (atrazine and ametryne) instead of the conventional hanging mercury drop electrode (HMDE) is reported. The results obtained using electroanalytical methods utilizing each of these electrodes were also compared with those provided by the HPLC technique. The results indicated that the CuSAE electrode can be used to detect the herbicides studied, since the detection limits reached using the electrode (3.06 microg L-1 and 3.78 microg L-1 for atrazine and ametryne, respectively) are lower than the maximum values permitted by CONAMA (Brazilian National Council for the Environment) for wastewaters (50 microg L-1) and by the US EPA (Environmental Protection Agency of the United States) in natural water samples (10.00 microg L-1). An electroanalytical methodology employing CuSAE and square wave voltammetry (SWV) was successfully applied to the determination of atrazine and ametryne in natural water samples, yielding good recoveries (70.30%-79.40%). This indicates that the CuSAE provides a convenient substitute for the HMDE, particularly since the CuSAE minimizes the toxic waste residues produced by the use of mercury in HDME-based analyses.

Electrochemical behavior of dopamine at a 3,3'-dithiodipropionic acid self-assembled monolayers

Monolayers of 3,3'-dithiodipropionic acid (DTDPA) were prepared on a polycrystalline gold electrode through a self-assembly procedure to produce a gold 3,3'-dithiodipropionic acid self-assembled monolayer (AuDTDPA) modified electrode. The characterization of the AuDTDPA electrode was investigated by cyclic voltammetry and ac impedance using the [Fe(CN)(6)](3-/4-) redox couple. The electrochemical behavior of DA on the modified electrode AuDTDPA was studied by cyclic and square-wave voltammetries, using phosphate buffer as supporting electrolyte. The oxidation peak current for DA increases linearly with concentration in the range of 0.35x10(-5) to 3.4x10(-5)molL(-1). The performance of the AuDTDPA modified electrode was evaluated for the electroanalytical determination of dopamine (DA) in a pharmaceutical formulation. The AuDTDPA modified electrode showed a stable behavior and the presence of surface-COOH groups avoided the passivation of the electrode surface during the dopamine oxidation.

Electrochemical degradation of carbaryl on oxide electrodes

This paper presents the study of a prospective electrochemical treatment system for the pesticide carbaryl. Three different dimensionally stable anodes were employed (Ti/Ru0.3 Ti0.7 O2, Ti/Ru0.3 Sn0.7 O2 and Ti/Ir0.3 Ti0.7 O2) and the effect of current density (10, 20, 40 and 60 mA cm(-2)) and supporting electrolyte (0.1 mol L(-1) NaCl and 0.033 mol L(-1) H2SO4) is discussed. All the electrodes present a low level of carbaryl and total organic carbon removal in H2SO4, even at highly positive potentials, indicating that the application of current is not, in itself, sufficient to promote effective oxidation of the pesticide and its products. However, in the presence of NaCl all the electrodes used present rapid diminishing of the carbaryl and total organic carbon content, thus suggesting enhanced activity. The results demonstrate the participation of partially oxidised Cl- species at the electrode surface, which act as an intermediate in the electron transfer between the pesticide molecule and the electrode. Thus, under such conditions, the feasibility of the electrochemical route for the treatment (total or partial) of waste that contains carbaryl is evident.

Oxidation of the pesticide atrazine at DSA electrodes

This paper presents the study of the electrochemical oxidation of the pesticide atrazine at a Ti/Ru(0.3)Ti(0.7)O(2) dimensionally stable anodes (DSA). The effect of using different supporting electrolytes (NaCl, NaOH, NaNO(3), NaClO(4), H(2)SO(4) and Na(2)SO(4)) during the galvanostatic electrolysis of atrazine was investigated. It was observed that the removal of atrazine and total organic carbon (TOC) was only achieved at appreciable rates when NaCl was used as the supporting electrolyte, due to the oxidising species formed in this electrolyte (e.g. ClO(-)). Variation of the NaCl concentration demonstrated that, although only low concentrations of NaCl are necessary to result in the complete removal of atrazine in solution, TOC removal is almost linearly dependent on the quantity of NaCl in solution. Examination of the applied current density indicates that the efficiency of TOC removal reaches a maximum at 60 mA cm(-2). Testing of alternative electrode materials containing SnO(2) did not improve the efficiency of atrazine removal in Na(2)SO(4), but in NaCl a small increase was observed. Overall there appears to be no great advantage in using SnO(2)-containing electrodes over the Ti/Ru(0.3)Ti(0.7)O(2) electrode.

Electroanalytical method for determination of the pesticide dichlorvos using gold-disk microelectrodes

This paper reports the use of laboratory-prepared gold microelectrodes and square-wave voltammetry for analytical determination of low concentrations of the pesticide dichlorvos in pure and natural water samples. After optimization of the experimental and voltammetric conditions, the best voltammetric responses-current intensity and voltammetric profile-were obtained in 0.1 mol L(-1) NaClO4 with f=100 s(-1), a=50 mV, and DeltaE(s)=2 mV. The observed detection and quantification limits in pure water were 7.8 and 26.0 microg L(-1), respectively. The reproducibility and repeatability of the method were also determined; the results were 1.4% (n=5) and 1.2% (n=10), respectively. Possible interfering effects were evaluated in natural water samples collected at different points with different levels of contamination from agricultural, domestic, or industrial waste from an urban stream. Results showed that the detection and quantification limits increased as a function of the quantity of organic matter present in the samples. Nonetheless, the values observed for these method characteristics were below the maximum value allowed by the Brazilian code for organophosphorus pesticides in water samples. Recovery curves constructed using the standard addition method were shown to be satisfactory compared with those obtained from high-performance liquid chromatography, confirming the suitability of the method for analysis of natural water samples. Finally, when the method was used to determine dichlorvos in spiked cows' milk samples, satisfactory recovery and relative standard deviations were obtained.