Amperometric Nitric Oxide Sensor Based on Carbon Paste Electrode Modified with Chromium (III) Oxide

Chromium (III) oxide was used as a bulk mediator in carbon paste electrodes to improve the performance of the carbon electrodes for the detection of nitric oxide in comparison with unmodified electrodes. The sensor could be operated as a detector in a flow injection analytical setup under physiological conditions (pH 7.5, 0.1 M phosphate buffer) with an operating potential from 650 mV to 700 mV (vs. Ag/AgCl), a flow rate of the carrier of 0.4 mL/min and an injection volume of 200 mL. The amperometric response of the sensor showed good linearity up to 300 µM with a sensitivity of about 0.644 nA/µM. The relative standard deviation for the repeatability of measurements for 100 µM NO was 3.9 % (n = 10 measurements) and the reproducibility was 12 % (n = 5 sensors). The effect of all investigated interferences (nitrite and nitrate ion) was not fatal and at 650 mV the signal ratio of NO/NO2- is around 10. The new sensor was successfully applied to the determination of NO in car exhaust fumes.