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Nowadays, the use of pesticides in world agriculture is fundamental. However, it leads to an increase in the illegal sale and smuggling of these products in various parts of the world, mainly in Brazil. Therefore, the development of new analytical methods for screening and analysis of these kind of substances is a relevant issue. We present in this work, for the first time, an electrochemical study and a novel electroanalytical method for determination of fungicide benzovindiflupyr (BENZO). According to our knowledge, the electrochemical behavior of BENZO, as well as its voltammetric determination, have never been reported before. The sensors used here consisted of disposable pencil graphite electrodes (PGEs). On this electrode surface and at optimal pH, BENZO behaved according to a quasi-reversible system and showed two voltammetric peaks, one anodic at E

This work describes a novel, simple and inexpensive pen-on-paper (PoP) method for patterning hydrophobic structures in paper substrates aiming the production of paper-based analytical devices (PADs). This fabrication protocol uses a commercially available plastic welding kit that can be easily acquired and is sold as a repair tool. It consists of an acrylate-based resin which is deposited on the paper and then cured using a UV led, or even the sunlight, for creation of the hydrophobic barriers. The protocol is instrument-free and can be easily implemented in any laboratory. To the best of our knowledge, this is the first report of the use of this material for production of analytical devices. The developed PADs were fully characterized and exhibited better chemical resistance than other recently reported PoP approaches regarding organic media and surfactants. Moreover, the fabrication method demonstrated good analytical versatility since it allowed the production of flexible devices, flow-based devices and pencil-drawn electrochemical devices. These findings are very interesting since overcome some limitations related by other PoP reports and expand the possibilities of using this technology in several aqueous and non-aqueous applications. Lastly, the analytical usefulness of the developed devices was successfully explored through colorimetric determination of nitrite. A detection limit of 0.14 mg L−1 was achieved and several samples of natural waters were analyzed. The results showed good agreement when compared with a reference technique. So, considering the simplicity and the results presented here, this fabrication method shows great potential for use in analytical chemistry.

In this work we propose the voltammetric analysis of contraceptive hormones ethinylestradiol (EE) and cyproterone acetate (CPA) using solid amalgam electrode fabricated with silver nanoparticles. To the best of our knowledge, this is the first report describing the simultaneous determination of these two compounds and also the first report of the use of amalgam electrode for analysis of EE and CPA. The voltammetric behavior of both substances was investigated by their reduction. An irreversible electrochemical process involving two protons and two electrons was found for each compound. The analytical assays were carried out using staircase voltammetry (SCV). Due to this, aiming to improve the analytical sensitivity, the cationic surfactant cetyltrimethylammonium bromide was also used. The instrumental and experimental parameters were studied and optimized to achieve the best conditions for the analysis. Under the optimum conditions, the voltammetric signals of EE and CPA showed dependence on the concentration range from 6.4 × 10−7 to 7.8 × 10−6 mol L−1 and from 1.0 × 10−6 to 1.0 × 10−5 mol L−1, respectively. The limits of detection obtained were 1.03 × 10−7 mol L−1 for EE and 2.99 × 10−7 mol L−1 for CPA. The analytical usefulness of the method was evaluated through its application on the simultaneous determination of EE and CPA in pharmaceutical formulations and urine samples. The two analytes were successfully quantified in these samples with good precision and the values found presented satisfactory concordance with the reference values, suggesting acceptable analytical efficiency for the approach described here.

A carbon paste electrode was used for the electrochemical determination of linuron concentrations in water and vegetable extracts. Optimal conditions were established with respect to electrode activation (electrochemical pretreatment), time accumulation, potential accumulation, scan rate, and pH. The limit of detection achieved with a pre-concentration step was 23.0 μg L−1. Recovery measurements in vegetable extract and natural water samples were in the range of 98–103%, indicating that the proposed electrochemical method can be employed to analyze linuron in these matrices. The determination results were in good agreement with HPLC results.

The direct amperometric determination of tert-butylhydroquinone (TBHQ) in biodiesel at an unmodified glassy carbon electrode is reported. A biodiesel aliquot was added into an electrochemical cell containing a 75% (v/v) ethanol-water solution under stirring (with final concentration of 50 mmol L(-1) HClO(4)). The amperometric method involved the continuous application of three sequential potential pulses to the working electrode (700 mV for 300 ms, 0 mV for 100 ms and -50 mV for 1s). TBHQ was continuously monitored at the first (direct oxidation) and optionally at the second (reduction) potential pulse while the third potential pulse was applied for cleaning of the electrode surface. For comparison, the samples were also analyzed by high-performance liquid-chromatography and a good agreement between the results was verified. Recovery values for spiked samples were between 90% and 95% and the reproducibility of the proposed method was around 5% (n=5). The proposed method can be easily adapted for on-site analysis.

A biosensor based on alfalfa sprout (Medicago sativa) homogenate as a source of peroxidase is proposedfor the determination of thiodicarb by square-wave voltammetry. This enzyme was immobilized in self-assembledmonolayersofl-cysteineonagoldelectrode.Severalparameterswereinvestigatedtoevaluatethe optimum conditions for operation of the biosensor. The analytical curve was linear for thiodicarbconcentrations of 2.27×10 −6 to 4.40×10 −5 molL −1 with a detection limit of 5.75×10 7 molL −1 . Thelifetime of the Au-alfalfa sprout–SAMs was 20 days (at least 220 determinations). The average recoveryof thiodicarb from samples of vegetable extracts ranged from 99.02 to 101.04%. The results obtained forthiodicarb in vegetable extracts using the proposed method are in close agreement with those using ahigh performance liquid chromatography procedure at the 95% confidence level.© 2010 Elsevier B.V. All rights reserved. 1. IntroductionSeveral toxic organic compounds (herbicides, fungicides, aca-ricides, and insecticides) have been used in agriculture to controldiseases and obtain high yields. Residues of these pesticides mayenter the food chains through air, water and soil and cause numer-ous health problems to ecosystems and humans. They can producebonemarrowdiseases,infertility,nervedisorders,andimmunolog-icalandrespiratorydiseases[1].Therefore,thepresenceofresiduesof pesticides in natural waters and in foods is of major concern forpublic health reasons [2].Carbamate compounds are used as pesticides on a large scaleworldwide due to their wide ranging biological activity. Thesepesticides include a broad-spectrum of insecticides widely usedas acaricides, molluscicides, nematocides and helmithicides [3,4].People involved in the manufacture or application of carbamatesmay be exposed to these pesticides in the general environmentor in the workplace [5]. Several carbamate compounds are highlytoxic to humans and other mammals. Carbamate acts by inhibit-ing the cholinesterase enzymes, especially acetylcholinesterase,leadingtoanaccumulationofacetylcholineinnervesynapses,trig-gering a series of parasympathomimetic effects. Carbamates arereversible inhibitors of colinesterases, but poisoning can be veryserious [6].

This paper introduces a simple, fast and reliable electroanalytical method for differential-pulse polarography based on electrochemical reduction at a dropping mercury electrode. The method was validated for the determination of 2-ethylhexyl-4-methoxycinnamate (EHMC) alone and in association with 4-methylbenzylidene camphor (MBC) or 2-hydroxy-4-methoxybenzophenone (BENZ-3) in samples of commercial cosmetic preparations. The supporting electrolyte that provided the best-defined and most intense peak current for EHMC determination was Britton-Robinson buffer (pH 4.0) in the presence of a cationic surfactant. Under optimized conditions, EHMC exhibited one single peak of reduction at −1.49 V versus Ag/AgCl. A limit of detection of 3.76 × 10 −8 mol L −1 and a limit of quantitation of 1.25 × 10 −7 mol L −1 were found for the pure EHMC standard. A good average recovery rate was reached for all the samples analyzed.