Method of chemical separation for nitrogen compounds in soils established by BREMNER (1965) was checked and modified to apply for the measurement of the natural variation in isotopic ratios of nitrogen compounds in sediments. Separation of nitrogen compounds which exist in different occurrences i.e., (a) in interstitial water, (b) in the exchangeable site on the surface of solid, and (c) in solid, was also studied, and the optimum conditions for the separation were determined.
