Optimization of Nitric Oxide Chemiluminescence Operating Conditions for Measurement of Plasma Nitrite and Nitrate

Abstract

The oxidized nitric oxide (NO) metabolites nitrite (NO2−) and nitrate (NO3−) have been used as markers of NO synthase activity in several clinical and experimental studies including those investigating sepsis (1)(2)(3)(4), septic shock (5), endotoxemia (6)(7), cardiac transplant (8), hypertension (9), and cancer (10). Although the NO chemiluminescence methodology has been used to measure NO2− and NO3− (11)(12)(13), there are few reports evaluating the operating conditions of the assay. The operating efficiency of the NO chemiluminescent system is governed by several variables: driving pressure and flow rate of the carrier gas (14)(15), which determine the degree of mixing in reducing solution and dispersion of NO in the carrier gas stream; chemiluminescent reaction chamber pressure ( P RC); and the selectivity (16), pH (11), temperature (13), and concentration of the reducing agents used to convert NO2− and NO3− to NO. Yang et al. (13) studied the efficiency of conversion of both NO2− and NO3− to NO using various reducing agents over a range of operating temperatures; however, no studies on the relationship between carrier gas flow rate and P RC have been reported. The present study had three primary objectives: ( a ) to determine the optimal operating conditions for carrier gas flow rate and P RC to achieve maximum efficiency of the chemiluminescent response for both NO2− and NO3− determinations; ( b ) to determine the detection limit and linearity of NO2− and NO3− responses on the basis of these optimal operating conditions; and ( c ) to evaluate the recovery of NO2− and NO3−from plasma and deproteinized plasma under optimized operating conditions. We …