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MonitorizaĆ§Ć£o de cobre em vinhos verdes
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Abstract(s)
A presente dissertaĆ§Ć£o descreve o desenvolvimento e a caracterizaĆ§Ć£o de
sensores potenciomĆ©tricos com base em polĆmeros de impressĆ£o molecular e de
sensores Ć³pticos com base em membranas de poli(cloreto de vinilo), PVC, para a
determinaĆ§Ć£o de cobre em vinhos verdes.
Os sensores potenciomƩtricos foram preparados a partir de diferentes
solventes (metanol e clorofĆ³rmio), tendo o seu crescimento decorrido na presenƧa ou
ausĆŖncia da molĆ©cula molde (cobre). Os sistemas sensores selectivos ao cobre
continham partĆculas de polĆmeros com ou sem impressĆ£o molecular como material
electroactivo, dispersas em solvente plastificante, PVC e, em alguns casos, aditivo
aniĆ³nico. A avaliaĆ§Ć£o dos vĆ”rios sistemas baseou-se na comparaĆ§Ć£o das
caracterĆsticas operacionais dos diversos elĆ©ctrodos onde foram aplicados. Estas
caracterĆsticas foram obtidas a partir de curvas de calibraĆ§Ć£o, cujos declives e limites
de detecĆ§Ć£o variaram entre -39,9 ā 37,0 mV decada-1 e 4,2 ā 29,1 Ī¼g mL-1,
respectivamente. Os sensores nĆ£o sĆ£o independentes do pH uma vez que o complexo
formado entre o cobre e a difenilcarbazida Ć© favorecido por valores de pH prĆ³ximos de
5. Assim, obtiveram-se melhores resultados usando Ć”gua desionizada ou soluĆ§Ć£o
tampĆ£o de HEPES revelando-se um mĆ©todo rĆ”pido e relativamente eficaz nestas
condiƧƵes.
Os sensores Ć³pticos basearam-se na reacĆ§Ć£o colorimĆ©trica entre o cobre e um
complexante. Os reagentes complexantes escolhidos foram a neocuproĆna, a
difenilcarbazida e o dietilditiocarbamato de sĆ³dio. Avaliou-se o efeito de vĆ”rios
parĆ¢metros experimentais na resposta destes sensores, tais como o pH (avaliado para
os valores 3,00 e 5,00), a concentraĆ§Ć£o de cobre (que variou entre 0,06 e 317,7 mg L-
1) e as prĆ³prias caracterĆsticas da membrana. Os melhores resultados foram obtidos a
pH 3, numa gama de concentraƧƵes de 0,06 e 31,8 mg L-1 usando a difenilcarbazida
como reagente complexante. A aplicaĆ§Ć£o destes sensores a vinhos requer ainda
estudos adicionais, especialmente no que diz respeito Ć necessidade de implementar
algum procedimento de prƩ-tratamento de amostra.
This dissertation describes the development and characterization of potentiometric sensors based on molecularly imprinted polymers and optical sensors based on membranes of poly(vinyl chloride), PVC, for the determination of copper in Vinho Verde. The potentiometric sensors were prepared with different solvents (methanol and chloroform) and its growth was carried out with or without template (copper). The sensor systems were dispersed in plasticizer, PVC, and in some cases, an anionic additive. Characterization of the potentiometric systems was made by comparison of the operational analytical features of the different electrodes. These features were obtained from calibration curves, whose slopes and detection limits ranged from -39.9 ā 37.0 mV decade-1 and 4.2 to 29.1 mg mL-1, respectively. The sensors were not independent from the pH since the complex formed between copper and diphenylcarbazide was favored by pH values near 5, thus, better results were obtained using deionized water or HEPES buffer. This method was considered quick and relatively effective under these conditions. Optical sensors were based on the colorimetric reaction between copper and a complexing reagent. Three different compounds were tested: neocuproine, diphenylcarbazide and sodium diethyldithiocarbamate. The effect of various experimental parameters on the response of these sensors was evaluated, such as pH (evaluated from 3.00 to 5.00), the copper concentration (varied between 0.06 and 317.7 mg L- 1) and the characteristics of the membrane. The best results were obtained with pH 3, in a concentration range of 0.06 and 31.8 mg L-1 using diphenylcarbazide as a complexing reagent. The practical application of the present method to wines requires, however, additional elements regarding the need to previous sample pretreatment procedure.
This dissertation describes the development and characterization of potentiometric sensors based on molecularly imprinted polymers and optical sensors based on membranes of poly(vinyl chloride), PVC, for the determination of copper in Vinho Verde. The potentiometric sensors were prepared with different solvents (methanol and chloroform) and its growth was carried out with or without template (copper). The sensor systems were dispersed in plasticizer, PVC, and in some cases, an anionic additive. Characterization of the potentiometric systems was made by comparison of the operational analytical features of the different electrodes. These features were obtained from calibration curves, whose slopes and detection limits ranged from -39.9 ā 37.0 mV decade-1 and 4.2 to 29.1 mg mL-1, respectively. The sensors were not independent from the pH since the complex formed between copper and diphenylcarbazide was favored by pH values near 5, thus, better results were obtained using deionized water or HEPES buffer. This method was considered quick and relatively effective under these conditions. Optical sensors were based on the colorimetric reaction between copper and a complexing reagent. Three different compounds were tested: neocuproine, diphenylcarbazide and sodium diethyldithiocarbamate. The effect of various experimental parameters on the response of these sensors was evaluated, such as pH (evaluated from 3.00 to 5.00), the copper concentration (varied between 0.06 and 317.7 mg L- 1) and the characteristics of the membrane. The best results were obtained with pH 3, in a concentration range of 0.06 and 31.8 mg L-1 using diphenylcarbazide as a complexing reagent. The practical application of the present method to wines requires, however, additional elements regarding the need to previous sample pretreatment procedure.
Description
Keywords
Cobre Vinhos verdes Sensores potenciomĆ©tricos PolĆmeros de impressĆ£o molecular Sensores Ć³pticos Cooper Green wines Potentiometric sensors Molecularly imprinted polymers Optical sensors
Pedagogical Context
Citation
Publisher
Instituto PolitƩcnico do Porto. Instituto Superior de Engenharia do Porto