Printed electrochemical sensor for ascorbic acid determination

Simple, strip-type sensors based on 7,7,8,8-tetracyanoquinodimethane-modified graphite were prepared using screen printing techniques. The electrochemical strips operated at low potentials 50 mV at pH 7.0 or 100 mV at pH 4.8 vs. Ag/AgCl (printed)] and had a sensitivity of 3.5–7.1 μA 1 mmol^?1L-ascorbic acid. Determination of ascorbic acid concentration was achieved in 30 s and required samples of ca. 30 μl. The current output of the electrodes was found to be relatively insensitive to variations in pH over the range 5.0–8.5. Between 15 and 35 °C, the temperature coefficient was 2.7% °C^?1. The printed electrodes were suitable for single determinations but demonstrated adequate stability for periodic re-use. The ascorbic acid concentration in the juice of fresh fruit was determined using the electrochemical printed electrodes and a commercially available enzymatic test kit. Close agreement was observed between the two methods r=0.9997 (n=12),slope=0.9798]. The limit of detection using the printed sensor for real samples was calculated as 4mg l^?1(22 μM).