The sequential determination of nitrite, N-nitroso compounds and nitrate and its application.
The selective determination of nitrite, N-nitroso compounds as a group and nitrate can be accomplished directly on most food or other matrices by quantifying the nitric oxide released following the additions in sequence of acetic acid, hydrogen bromide and titanous chloride under an atmosphere of nitrogen. Most of the many other compounds potentially formed from nitrite in a biological system are either decomposed to nitric oxide in the refluxing solvent system alone or else do not yield nitric oxide at any stage throughout the determinations of nitrite and N-nitroso compounds. Only nitrolic acids and S-nitrothiols, like nitrosamines and nitrosamides, require the use of hydrogen bromide for breakdown to nitric oxide. The application of the present procedure to the determination of nitrite and N-nitroso compounds (as a group) in a series of animal diets has shown the presence of levels of nitrite below the limit of detection of more conventional methods, even in those diets not deliberately treated with nitrite. Evidence was also obtained for the presence of non-volatile, non-extractable N-nitroso compounds in diets both treated and untreated with high levels of nitrite. Confirmation was provided in the case of one diet not treated with nitrite, in that it was found to convert morpholine into its N-nitroso derivative, which was detected by gas chromatography with a Thermal Energy Analyzer detector.