Evaluation of a nafion coated glassy carbon electrode for determination of paraquat by differential pulse voltammetry

Abstract

Este trabalho apresenta uma avaliação de um eletrodo de carbono vítreo recoberto com filme de Nafion para a determinação de paraquat em águas de rio e urina por voltametria de pulso diferencial. O filme foi formado adicionando-se 4 µL de uma solução de Nafion 4% (m/v) na superfície do eletrodo, seguindo-se evaporação do solvente com luz infra-vermelha. A máxima relação sinal/ruído foi obtida em meio de tampão Britton-Robinson 40 mmol L -1 com pH 12 como eletrólito suporte. Utilizando-se um tempo de acumulação de 5 min em circuito aberto, o limite de detecção foi de 0,7 µg L -1 , enquanto o limite de quantificação foi de 1,0 µg L -1 , com uma faixa de resposta linear até 12 µg L -1 . Nestas condições, uma série de dez experimentos revelou um desvio padrão relativo de 2,2% para uma solução de paraquat 10 µg L -1 . A formação de par iônico em solução foi o principal fator de erro nas análises. Apesar do filme evitar a adsorção de espécies aniônicas na superfície do eletrodo, o paraquat sofre fortes associações em solução com substâncias húmicas, proteínas, argilas, surfactantes aniônicos, etc. Estas interações diminuem a acumulação do paraquat no filme de Nafion e, em conseqüência, diminuem a magnitude da corrente de pico de redução, requerendo que as quantificações sejam feitas por adição de padrão. Recuperações entre 87 e 106% foram obtidas para amostras de água de rio e urina enriquecidas aos níveis de 1,0 e 3,0 µg L -1 . This paper presents an evaluation of a Nafion coated glassy carbon electrode for determination of paraquat in river water and urine by differential pulse voltammetry. The film was formed applying 4 µL of a 1% (m/v) Nafion solution, which was evaporated under an infrared light. The maximum signal to noise ratio was obtained using a 40 mmol L -1 Britton-Robinson buffer at pH 12 as supporting electrolyte. For an accumulation time of 5.0 min in open circuit, the limit of detection was 0.7 µg L -1 , while the quantification limit was 1.0 µg L -1 , with a linear dynamic range up to 12 µg L -1 . In these conditions, a sequence of ten experiments lead to a relative standard deviation of peak current of 2.2% for a 10 µg L -1 paraquat solution. Ion pair formation in solution was the major factor of error in analysis. Despite the film to avoid adsorption of anionic species at the electrode surface, paraquat suffers strong association in solution with humic substances, proteins, clays, anionic surfactants, etc. These interactions decrease the accumulation of paraquat in the Nafion film and, as a consequence, the magnitude of the reduction peak, requiring that quantifications have to be made by standard addition. Recoveries between 87 and 106% were obtained for river waters and urine samples spiked with 1.0 and 3.0 µg L -1 paraquat.Keywords: paraquat determination, river water, urine, modified electrode, voltammetry, ion exchange IntroductionParaquat (1,1'-dimethyl-4,4'-bypiridilium ion), also known as methyl viologen, is a defoliant and desiccant agent used to control herbal growth in terrestrial and aquat...

Deutscher Brückenbaupreis 2014 und 24. Dresdner Brückenbausymposium

“…1‐A) presented a faradaic signal related to reduction reaction on potential range between −0.55 and −0.60 V (vs. Ag/AgCl 3.0 mol L −1 KCl). This electrochemical process could be attributed to direct reduction of the paraquat dication to radical cation form summarized by a reaction involving one electron (PQ 2+ +1e − ${ \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightharpoonup\over {\smash{\leftharpoondown}}$}} }$ PQ •+ ) 22. This result suggests a PQ 2+ preconcentration at CPE which could be associated to hydrophobic interactions between graphite and PQ 2+ 23.…”

Electrochemical sensor based on nanostructured ion imprinted polymer for the sensing and extraction of Cr(III) ions from industrial wastewater

“…About 1.0 mg of Cr(III) ion imprinted MWCNT‐IIP was added to 1 mL of 0.5% Nafion solution and homogenized in a mortar for 10 min. Nafion solution was used in this study for the fixation of imprinted polymer to the platinum electrode surface . The final paste was fabricated on the platinum electrode surface and allowed to dry at room temperature; it is designated Pt‐MWCNT‐IIP.…”

“…Nafion solution was used in this study for the fixation of imprinted polymer to the platinum electrode surface. 14,15 The final paste was fabricated on the platinum electrode surface and allowed to dry at room temperature; it is designated Pt-MWCNT-IIP. Phosphate buffer was used in this study to supply conductivity for the paste fabricated on the platinum electrode.…”

Development and Application of Electrochemical Sensor Based on Molecularly Imprinted Polymer and Carbon Nanotubes for the Determination of Carvedilol

“…The influence of Nafion® 5% (m/v) on the performance of the sensor was also evaluated. Nafion® is a polymeric resin with excellent properties, such as chemical, mechanical, and thermal stability, selectivity for different cations, and high conductivity [36,37]. This polymer has been widely used for the fixation of particles onto electrode surface.…”