SCREEN-PRINTED ELECTRODE MODIFIED WITH SILVER HEXACYANOFERRATE-NAFION® FOR ASCORBIC ACID DETERMINATION

A flow injection system using a new and/or re-used graphite screen-printed electrode modified with silver hexacyanoferrate and a Nafion (R) polymer layer (AgHCF/GSPE) was employed for the determination of ascorbic acid in orange juice and drugs samples. Both modified electrodes showed an initial sensitivity of 0.015 A.cm(-2).M-1, with a linear response over the range from 50 to 300 mu L-1, relative standard deviations smaller than 2%, detection and quantification limits of e.a. 5.0 and 25.0 mg.L-1. The response of the electrodes was stable, with no variation of base line after 6-8 hours of continuous operation. With this system it is possible to measure 65-70 samples (20 mu L) per hour. By using 1.06 mg of AgNO3, 4.12 mg of K3Fe(CN)(6), 50.5 meal KNO3, and 800 mu L of HNO3, it is possible to obtain between 25 and 30 modified electrodes. The proposed system showed to be inexpensive, versatile, robust and suitable. for industrial application. The surface morphology of the bare and/or modified graphite screen-printed electrode was characterized by scanning electron microscopy.