An optical membrane redox chemical sensor for the determination of ascorbic acid

The redox indicator, ferroin, tris(1,10-phenanthroline)iron(II) was incorporated into the perfluorosulfonated cation-exchange membrane Nafion and, together with optical fibers, a photodiode, and a light-emitting diode, was used for the construction of a redox optical sensor (optode). The optode was incorporated in the flow-through cell of a computer-controlled sequential injection (SI) system and used for the determination of ascorbic acid (vitamin C). A linear relationship between the logarithm of the ascorbic acid concentration and the membrane absorbance was obtained for the concentration range from 2.50 × 10⁻³ to 1.00 × 10⁻¹ mol L⁻¹ and a sample frequency of 17 h⁻¹. The concentration of ascorbic acid determined in a number of commercial pharmaceutical products agreed well with iodometric titration results. This result shows that the SI system incorporating the ferroin/Nafion optode is suitable for the automated analysis of ascorbic acid in pharmaceutical products. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:200–204, 2000