This article describes the method for fractionation of N isotope based on the exchange of nitrogen isotopes in the system consisting of liquid mixtures of nitric acid and nitrogen oxides and the gaseous nitrogen oxide in the temperature range between 233 and 263 K under atmospheric pressure developed by the authors. The chemical interactions occurring between liquid nitric acid and gaseous nitrogen oxide at low temperatures and the equilibrium of the nitrogen isotopes exchange has been studied by means of the analysis of each co-existing phase in a packed column with counter-current movement of liquid and gas phases. The results obtained by theoretical modeling and experimental testing of the experimental plant have allowed one to conclude that the low temperature NITROX method is promising for the large-scale N production. This method improves upon the main technological parameters of the process as compared to traditional room temperature NITROX system. It allows for increasing the productivity of the same column and the degree of N extraction from the feed nitric acid up to two times, and for decreasing almost twice the consumption of sulphur dioxide (which is used to convert HNO3 to NO).