Determination of nitric oxide using horseradish peroxidase by UV second-order derivative spectrometry.

Based on the reaction of horseradish peroxidase (HRP) with nitric oxide (NO), a novel detection method of NO has been developed. The method uses second-order derivative spectrometry in an anaerobic phosphate buffer solution. The effects of pH and HRP concentration on the determination of NO in HRP system were investigated, and the conditions for the measurements were optimized. Some possible coexisting substances, such as nitrite, nitrate and hydrogen peroxide, were tested. The linear regression equation of standard curve was found to be h = 8.89 x 10(-2)c(NO)-1.56 x 10(-3) with the relevant coefficient of 0.9966 (n = 5) in the NO concentration range of 0.085-1.3 microM. The relative standard deviations were less than 3%. Based on the standard deviation of 5 blank measurements and a signal-to-noise ratio of 3, the detection limit for NO was 0.032 microM. The proposed method was successfully applied to the determination of NO levels in serum samples.