A POLAROGRAPHIC METHOD FOR MEASURING DISSOLVED NITRIC-OXIDE

A polarographic method for measuring the concentration of authentic ni tric oxide (NP) in aqueous solutions is described. When solutions of N O were injected into aqueous solutions containing dissolved oxygen, NO reacted with oxygen to give nitrite. The amount of nitrite formed in this reaction (analyzed by capillary electrophoresis) was compared wit h the amount of oxygen consumed (measured by polarography). We observe d a linear relationship between the amount of consumed oxygen and the amount of nitrite formed in the measured range (20-100 nmol NO2-) (R-2 = 0.89). These results demonstrate that polarographic measurements of the amount of oxygen consumed in the reaction with NO could be used t o estimate the concentration of dissolved NO in authentic NO solutions . There are several advantages to measuring consumed oxygen by polarog raphic methods: The method is simple and can be performed immediately prior to utilization of the NO solutions, it does not require any NO c alibration standards and it fully discriminates between NO and oxidati on products of NO. An additional advantage is, therefore, that stock s olutions of NO can be stored for an indefinite period of time prior to measurement. Both the preparation of authentic NO solutions and the m easurement of their NO content are therefore simplified. We also demon strate that a slow infusion of authentic NO solution to cell suspensio ns in vitro makes it possible to study the rapid, reversible biologica l effects of NO. (C) 1997 Elsevier Science B.V.