A polarographic method for measuring dissolved nitric oxide

A polarographic method for measuring the concentration of authentic nitric oxide (NP) in aqueous solutions is described. When solutions of NO 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 with the amount of oxygen consumed (measured by polarography). We observed 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 to estimate the concentration of dissolved NO in authentic NO solutions. There are several advantages to measuring consumed oxygen by polarographic methods: The method is simple and can be performed immediately prior to utilization of the NO solutions, it does not require any NO calibration standards and it fully discriminates between NO and oxidation products of NO. An additional advantage is, therefore, that stock solutions of NO can be stored for an indefinite period of time prior to measurement. Both the preparation of authentic NO solutions and the measurement of their NO content are therefore simplified. We also demonstrate that a slow infusion of authentic NO solution to cell suspensions in vitro makes it possible to study the rapid, reversible biological effects of NO. (C) 1997 Elsevier Science B.V.