Indirect Measurement of Nitric Oxide Production by Monitoring Nitrate and Nitrite Using Microchip Electrophoresis with Electrochemical Detection

An indirect method for monitoring nitric oxide (NO) by determining nitrate and nitrite using microchip capillary electrophoresis (CE) with electrochemical (EC) detection has been developed. This method combines determination of nitrite by direct amperometric detection following a microchip-based CE separation and conversion of nitrate to nitrite by chemical reduction using Cu-coated Cd granules. The amount of nitrate is quantified by calculating the difference in the amount of nitrite in the sample before and after the reduction of nitrate. Optimization of the separation, injection, detection, and reduction reaction conditions, as well as studies involving integration of the reduction reaction onto the microchip, are described. It was found that nitrite can be separated and detected in approximately 45 s by microchip CEEC. The reduction reaction was successfully integrated on-chip and carried out in approximately 1 min following activation of the Cd granules. The usefulness of this device was demonstrated by monitoring the amount of nitrate and nitrite produced from 3-morpholinosydnonimine, a NO-releasing compound.