Kinetic study of the decomposition of nitrite to nitrate in acid samples using Raman spectroscopy

Raman spectroscopy was employed as a means of determining the rate of decomposition of nitrite in solutions at various pH values. Nitrite decomposes with time in acidic medium, with an increase in decomposition rate as the concentration of acid increases. The mean decomposition rate of 0.625 mol/L NO2- in 1 mol/L HCl is 1.18 x 10(-5) s(-1), with t(1/2) = 16 h. This rate explains the problems encountered when the flow injection analysis (FIA) version of the Shinn reaction is applied to certain nitrite samples mainly from acidic origin. Nitrite is potentially unstable, and all food and water samples should be analyzed as soon as possible after collection. If it is necessary to store the samples prior to analysis, the effects of the storage conditions on the stability of the analyte must be established in prior trials.