Desenvolvimento de sensor eletroquímico baseado em polímero molecularmente impresso para determinação de hexahidrofarnesol em bioquerosene de aviação.
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Data
2018-02-23
Autores
Buffon, Edervaldo
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Universidade Estadual Paulista (Unesp)
Resumo
A atual expansão do setor de aviação tem aumentado à dependência das companhias aéreas ao querosene de aviação e a outros derivados fósseis. A dependência desse setor para com esses combustíveis se reflete em grandes índices de poluição atmosférica devido à emissão do CO2 proveniente da queima dessas substâncias. Tendo em vista a necessidade de reduzir esse poluente, têm-se desenvolvido novas tecnologias para a produção de querosenes alternativos de aviação (bioquerosenes de aviação). Uma das formas de obtenção do bioquerosene de aviação é a partir da fermentação de açúcares. O biocombustível obtido através dessa rota tecnológica é composto basicamente pelo farnesano e possui como principal contaminante o hexahidrofarnesol. A preocupação com a presença do hexahidrofarnesol no bioquerosene de aviação se deve principalmente a sua solubilidade em água e a degradação dos componentes do sistema de combustível. Diante disso, se fazem necessárias metodologias analíticas simples, sensíveis, seletivas e de baixo custo para determinar esse contaminante no bioquerosene de aviação. Uma vez que essas características são encontradas nos sensores eletroquímicos, o objetivo deste trabalho consiste no desenvolvimento de um sensor eletroquímico baseado em polímero molecularmente impresso para a determinação de hexahidrofarnesol em bioquerosene de aviação. O sensor proposto foi preparado pela eletropolimerização da o-fenilenodiamina sobre um eletrodo de carbono vítreo na presença da molécula de hexahidrofarnesol pela técnica de voltametria cíclica. O eletrodo modificado foi caracterizado por várias técnicas, tais como voltametria cíclica, espectroscopia de impedância eletroquímica, microscopia eletrônica de varredura, espectroscopia RAMAN e microscopia de força atômica. Os parâmetros que influenciam o desempenho do sensor impresso, como a razão molar entre o monômero funcional e a molécula molde, o número de ciclos utilizados na eletropolimerização, o pH da solução utilizada durante a eletropolimerização, o tempo de extração da molécula molde e o tempo de religação da molécula de hexahidrofarnesol nas cavidades impressas do sensor foram otimizados. O sensor desenvolvido apresentou duas faixas lineares de trabalho, de 5,0x10-8 a 1,5x10-7 mol L-1 e de 1,5x10-7 a 1,5x10-6 mol L-1. As constantes de dissociação aparente (Kd) para a primeira e a segunda faixa linear desse dispositivo foram calculadas pela isoterma de adsorção de Langmuir como sendo 4,8x10-7 e 9,1x10-6 mol L-1 respectivamente. As figuras de mérito, tais como sensibilidade, limite de detecção e limite de quantificação foram obtidas utilizando a primeira faixa linear e foram estimadas em 67 A L mol-1; 1,2x10-8 mol L-1 e 4,1x10-8 mol L-1 respectivamente. Na presença de moléculas potencialmente interferentes que compõem o bioquerosene de aviação, o sensor GCE-MIP demonstrou-se seletivo para o reconhecimento da molécula de hexahidrofarnesol. Além disso, esse sensor apresentou considerável repetibilidade inter-dia e intra-dia, com valores de RSD ≤ 4,8%, e teve 96% de sua corrente inicial preservada após ser armazenado por 10 dias em contato com o ar à temperatura ambiente. O método desenvolvido foi aplicado com sucesso na determinação de hexahidrofarnesol em bioquerosene de aviação. As recuperações médias variaram de 97,6% a 105,8%, com RSDs entre 1,7% a 3,9%, indicando que o método desenvolvido possui uma boa exatidão para a determinação de hexahidrofarnesol.
Current expansion of the aviation sector has increased the dependence of airlines to aviation kerosene and other fossil derivatives. Dependence of this sector to such fuels is reflected in high rates of air pollution due to the emission of CO2 originated from burning of these substances. In view of the need for lower emissions these pollutants, new technologies have been developed for the production of alternative aviation kerosene (aviation biokerosene). One of the ways of get the aviation biokerosene is from the fermentation of sugars. The biofuel obtained through this technological route is basically composed of farnesane, and it has as main contaminant the hexahydrofarnesol. The concern with the presence of hexahydrofarnesol in aviation biokerosene is mainly due to its solubility in water and the degradation of fuel system components. Thus, the developments of simple, sensitive, selective and low cost analytical methodologies to determine such contaminant in the aviation biokerosene are necessary. Once these characteristics are found in the electrochemical sensors, the objective of this work consists in the development of an electrochemical sensor based on molecularly imprinted polymer for the determination of hexahydrofarnesol in aviation biokerosene. The proposed sensor was prepared by electropolymerization of the o-phenylenediamine on a glassy carbon electrode in the presence of the hexahydrofarnesol molecule by the cyclic voltammetry technique. The modified electrode was characterized by several techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, RAMAN spectroscopy, and atomic force microscopy. Parameters that influence the performance of the imprinted sensor, such as the molar ratio between the functional monomer and the template molecule, the number of cycles used in the electropolymerization, the pH of the solution used during the electropolymerization, the extraction time of the template molecule and the time of rebinding of the hexahydrofarnesol molecules in the imprinted cavities were optimized. The developed sensor presented two linear ranges of work, 5.0x10-8 to 1.5x10-7 mol L-1 and 1.5x10-7 to 1.5x10-6 mol L-1. Apparent dissociation constants (Kd) for the first and second linear range of this device were calculated by Langmuir adsorption isotherm as being 4.8x10-7 and 9.1x10-6 mol L-1 respectively. Figures of merit, such as sensitivity, limit of detection and limit of quantification were obtained using the first linear range and were estimated in 67 A L mol-1; 1.2x10-8 mol L-1 and 4.1x10-8 mol L-1 respectively. In the presence of potentially interfering molecules that compose the aviation biokerosene, the GCE-MIP sensor showed up selective for recognition of the hexahydrofarnesol molecule. In addition, this sensor showed considerable inter-day and intra-day repeatability, with RSD values ≤ 4.8%, and had 96% of its initial current preserved after to be stored for 10 days in contact with the air at room temperature. The developed method was successfully applied in the determination of hexahydrofarnesol in aviation biokerosene. Average recoveries varied from 97.6% to 105.8%, with RSDs between 1.7% and 3.9%, indicating that the developed method had good accuracy for the determination of hexahydrofarnesol.
Current expansion of the aviation sector has increased the dependence of airlines to aviation kerosene and other fossil derivatives. Dependence of this sector to such fuels is reflected in high rates of air pollution due to the emission of CO2 originated from burning of these substances. In view of the need for lower emissions these pollutants, new technologies have been developed for the production of alternative aviation kerosene (aviation biokerosene). One of the ways of get the aviation biokerosene is from the fermentation of sugars. The biofuel obtained through this technological route is basically composed of farnesane, and it has as main contaminant the hexahydrofarnesol. The concern with the presence of hexahydrofarnesol in aviation biokerosene is mainly due to its solubility in water and the degradation of fuel system components. Thus, the developments of simple, sensitive, selective and low cost analytical methodologies to determine such contaminant in the aviation biokerosene are necessary. Once these characteristics are found in the electrochemical sensors, the objective of this work consists in the development of an electrochemical sensor based on molecularly imprinted polymer for the determination of hexahydrofarnesol in aviation biokerosene. The proposed sensor was prepared by electropolymerization of the o-phenylenediamine on a glassy carbon electrode in the presence of the hexahydrofarnesol molecule by the cyclic voltammetry technique. The modified electrode was characterized by several techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, RAMAN spectroscopy, and atomic force microscopy. Parameters that influence the performance of the imprinted sensor, such as the molar ratio between the functional monomer and the template molecule, the number of cycles used in the electropolymerization, the pH of the solution used during the electropolymerization, the extraction time of the template molecule and the time of rebinding of the hexahydrofarnesol molecules in the imprinted cavities were optimized. The developed sensor presented two linear ranges of work, 5.0x10-8 to 1.5x10-7 mol L-1 and 1.5x10-7 to 1.5x10-6 mol L-1. Apparent dissociation constants (Kd) for the first and second linear range of this device were calculated by Langmuir adsorption isotherm as being 4.8x10-7 and 9.1x10-6 mol L-1 respectively. Figures of merit, such as sensitivity, limit of detection and limit of quantification were obtained using the first linear range and were estimated in 67 A L mol-1; 1.2x10-8 mol L-1 and 4.1x10-8 mol L-1 respectively. In the presence of potentially interfering molecules that compose the aviation biokerosene, the GCE-MIP sensor showed up selective for recognition of the hexahydrofarnesol molecule. In addition, this sensor showed considerable inter-day and intra-day repeatability, with RSD values ≤ 4.8%, and had 96% of its initial current preserved after to be stored for 10 days in contact with the air at room temperature. The developed method was successfully applied in the determination of hexahydrofarnesol in aviation biokerosene. Average recoveries varied from 97.6% to 105.8%, with RSDs between 1.7% and 3.9%, indicating that the developed method had good accuracy for the determination of hexahydrofarnesol.
Descrição
Palavras-chave
Sensor eletroquímico, Eletrodo modificado, Polímero molecularmente impresso, o-fenilenodiamina, Hexahidrofarnesol, Bioquerosene de aviação, Electrochemical sensor, Modified electrode, Molecularly imprinted polymer, o-phenylenediamine, Hexahydrofarnesol, Aviation biokerosene