Ac ascorbico

Experimental
2 . 1 . Apparatus
A single-beam GBC 911A microprocessor-con- trolled UV-VIS spectrophotometer supplied by GBC Scientific Equipment Pty Ltd. with 1 mm optical path length quartz cells from STARNA was used for all absorbance measurements. This instrument was controlled via a BRAVO AST/ 30286 microcomputer connected by means of a serial port for data acquisition and data processingusing SCAN MASTER V 1.62 program (from GBC). All of the spectra were registered with a scan rate of 250 nm/min. A COMX PL80 plotter was used for graphical representations. An Agitaser 2000 rotating agitator and a Selecta Model Ultrasons ultrasonic bath were also used for stirring the glass tubes and dissolving the samples, respectively.
Un solo haz GBC 911A microprocesador controladoEspectrofotómetro UV-VIS suministrado por GBC Scientific Equipment Pty Ltd con 1 mm de camino óptico células longitud de cuarzo de Starna se utilizó para todas las mediciones de absorbancia. Este instrumento se controla a través de un BRAVO AST / 30286 microcomputadora conectada por medio de un puerto serie para la adquisición de datos y procesamiento de datos usando SCAN MAESTRO V 1.62 programa (de GBC). Todoslos espectros se registraron con una velocidad de barrido de 250 nm /min. Un plotter COMX PL80 se utiliza para representaciones gráficas. Un Agitaser 2000 agitador giratorio y un baño de ultrasonidos Selecta Modelo Ultrasons también se utilizaron para agitar los tubos de vidrio y la disolución de las muestras, respectivamente.
2 . 2 . Reagents
All chemicals used were of analytical-reagent gradeand doubly distilled water was always used.
Todos los productos químicos utilizados fueron de grado reactivo analítico y siempre fue agua doblemente destilada
2 . 2 . 1 . L ( + ) -ascorbic acid solutions
( Panreac ) Only aqueous fresh solutions, prepared from a 100 mg l−1 solution (daily prepared), were used for the spectrophotometric measurements. The 100 mg l−1 stock solution was stable forat least 6 h stored at 4°C. Soluciones acuosas frescas preparadas a mg/L (preparación diaria) fueron usadas en la medición espectrofotométrica. La solución stock 100 mg/L es estable por al menos 6 horas a 4°C
2 . 2 . 2 . pH Buffer solution. A total of 0.952 g of Na2B4O7 10H2O were dissolved in 80 ml of doubly distilled water, the pH was adjusted to 8.0 by adding 4 M hy- drochloric acid, and thesolution was diluted to 100 ml. Solucion buffer. 0.952 g de Na2B4O7 10H20 se disolvieron en 80
mL de agua doblemente destilada, el pH se ajusto a 8.0 con HCl 4 M y la solución se diluyo a 100 mL
2 . 2 . 3 . Sephadex QAE A- 2 5 ( Aldrich ) ion-exchanger (40 – 120 mm ) The resin was used in the chloride form in its original dry state in order to avoid any contamination.
La resina se utiliza enforma de cloruro en su estado original en seco con el fin de evitar cualquier contaminación
2 . 3 . Absorbance measurements
After ascorbic acid was sorbed on Sephadex QAE A-25 resin, it was introduced into a 1 mm optical quartz cell and the absorbance was mea- sured directly on it at two wavelengths, 267 and 400 nm, A267 and A400 (the former corresponding to the absorption maximum and the latterin- cluded in the range where only the resin absorbs light) against a 1 mm cell packed with resin previously equilibrated with a blank solution. The net absorbance A, was obtained by the difference between both values: A=A267−A400.
Después de poner el acido ascórbico en la resina es introducido en una célula de cuarzo óptico de 1 mm y se midio la absorbancia directamente sobre ella en doslongitudes de onda, 267 y 400 nm , A267 y A400 ( la antigua correspondiente a el máximo de absorción y la segunda en el rango donde sólo la resina absorbe la luz ) contra una célula 1 mm rellena con resina previamente equilibrada con una solución en blanco . La absorbancia neta A, se obtuvo la diferencia entre ambos valores: a = A267 - A400 .
2 . 4 . General procedure
An adequate volume of aqueous...