DIRECT REDUCTIVE AMPEROMETRIC DETERMINATION OF NITRATE AT A COPPER ELECTRODE FORMED INSITU IN A CAPILLARY-FILL SENSOR DEVICE

A method has been developed for determining nitrate amperometrically by direct reduction at a freshly deposited copper electrode surface in a capillary-fill device (CFD). Copper(II) is added to the nitrate sample which is then taken up into the device. The potential of the screen-printed carbon electrode is held at -0.75 V versus the screen-printed silver reference electrode. At this potential, copper is plated onto the carbon electrode forming a freshly prepared copper electrode. At the same time dissolved oxygen is reduced. The potential is then scanned to more negative potentials and the signal at -0.90 V, due to the reduction of the nitrate, is measured. The method for determining nitrate given here is preliminary to the production of CFDs in which chemical reagents, copper sulphate and potassium hydrogen sulphate (used to produce the acidity), are screen-printed or otherwise coated onto the upper plate within the device.