Electrical and Electrochemical Behavior of Carbon Paste Electrodes Modified with Ionic Liquids Based in N-Octylpyridinium Bis(Trifluoromethylsulfonyl)Imide. A Theoretical and Experimental Study.

In this work, we studied carbon paste electrodes (CPEs) with two kinds of binders: mineral oil or ionic liquids (IL) derived from N-substituted octyl pyridinium bis(trifluoromethylsulfonyl)imide with the substituents H-, CH3-, CN- and CF3-. The work aims to study this series of IL and determine a possible effect of the substituent of the cation in the behavior of the IL as a binder of graphite for obtaining IL-CPEs. The electrochemical response and the electrical behavior were measured by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Surprisingly, the substituent does not affect the cyclic voltammetry response because in all the cases, high resistance and high capacitive currents were obtained. The best response in terms of conductivity is obtained by CPE. In the case of impedance measurements, the substituent does not cause differences, and in all the cases, the IL-CPEs show nearly the same responses. CPE shows lower capacitance and higher resistance for diffusion compared to the IL-CPEs due to his lower porosity. The high resistance showed by the IL-CPEs by cyclic voltammetry can be attributed to poorly intermolecular forces among graphite, water, electrolyte, and ILs as demonstrated by theoretical calculations.

Extraction and quantification of SO2 content in wines using a hollow fiber contactor.

Sulfites [Formula: see text] or sulfur dioxide (SO2) is a preservative widely used in fruits and fruit-derived products. This study aims to propose a membrane contactor process for the selective removal and recovery of SO2 from wines in order to obtain its reliable quantification. Currently, the aspiration and Ripper methods offer a difficult quantification of the sulfite content in red wines because they involve evaporation steps of diluted compounds and a colorimetric assay, respectively. Therefore, an inexpensive and accurate methodology is not currently available for continuous monitoring of SO2 in the liquids food industry. Red wine initially acidified at pH < 1 was treated by membrane extraction at 25 ℃. This operation is based on a hydrophobic Hollow Fiber Contactor, which separates the acidified red wine in the shell side and a diluted aqueous sodium hydroxide solution as receiving solution into the lumenside in countercurrent. Sulfite and bisulfite in the acidified red wine become molecular SO2, which is evaporated through the membrane pores filled with gas. Thus, SO2 is trapped in a colorless solution and the membrane contactor controls its transfer, decreasing experimental error induced in classical methods. Experimental results using model solutions with known concentration values of [Formula: see text] show an average extraction percentage of 98.91 after 4 min. On the other hand, two types of Chilean Cabernet Sauvignon wines were analyzed with the same system to quantify the content of free and total sulfites. Results show a good agreement between these methods and the proposed technique, which shows a lower experimental variability.

Anthocyanin composition in aged Chilean Cabernet Sauvignon red wines.

Anthocyanins in aged Cabernet Sauvignon red wines were studied by HPLC-MS. The major anthocyanin in 6, 7, and 8year old red wine extracts was the dimer vitisin A produced by condensation of malvidin-3-O-glucoside mediated by pyruvic acid. In aged wine, the content of malvidin-3-O-glucoside decreased with age with a concomitant increase of vitisin A. The latter is accompanied by several condensation products with molecular weight up to 1500m/z. Differential pulse voltammetry indicated that aged wines have lower antioxidant capacity than young wine (400mV), but higher than malvidin-3-O-glucoside (483mV). Tafel's plots showed that the electrochemical process occurring in aged wines is different from young wines. Six, seven and eight year old wines show similar behaviour with plots of 234, 177 and 188mV/dec, respectively. These values are higher than the expected 120mV/dec corresponding to a first electronic transfer but smaller compared to the 523mV/dec corresponding to young wine.