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 de composes with time in acidic medium, with an increase in decomposition rate as the concentration of acid increases. The mean decomposition r ate 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 potentia lly unstable, and all food and water samples should be analyzed as soo n as possible after collection. If it is necessary to store the sample s prior to analysis, the effects of the storage conditions on the stab ility of the analyte must be established in prior trials.