Development of a modified copper-cadmiumreduction method for rapid assay of total nitric oxide

Abstract

The biomolecule, nitric oxide (NO) is short lived and is converted to two stable products—nitrite (NO₂) and nitrate (NO₃). NO₃ can be measured by colorimetric procedure involving enzymatic conversion to NO₂ and by HPLC. But these methods, though sensitive and specific, require expensive reagents or equipment. Reduction of NO₃ to NO₂ by copper-coated cadmium granules is a popular method devised by Cortas and Wakid (Clin. Chem., 1990, 36, 1440), but it takes 120 min. Our aim of this study is to modify the Cortas and Wakid method for rapid reduction of NO₃ to NO₂ for total NO estimation in serum. After reduction, NO₂ is estimated by Griess reaction. As per our results, complete reduction of NO₃ could be achieved by both the methods, but it took only 5 min by our method. Standard graphs were linear by both of the methods. Factors were found to be 143.4 and 196.7 by the Cortas and Wakid method and by our method, respectively. Recovery of NO₂ from NO₃ was found to be 105% and 106%, respectively. We measured total NO₂ in sixteen sera by both the methods and our method's coefficient of correlation was found to be 0.9924. Our method is comparable to that of Cortas and Wakid for complete reduction of NO₃ with the greatest advantage of decrease in the time span from 120 to 5 min. This is due to our development of an increased copper coating method on cadmium granules. Our rapid method saves much time for total NO estimation.