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-mu-A 1 mmol-1 L-ascorbic acid. Determination of ascorbic acid concentration was achieved in 30 s and required samples of ca. 30-mu-l. 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-degrees-C, the temperature coefficient was 2.7%-degrees-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 4 mg l-1 (22-mu-M).