Determination of traces of water in liquid dinitrogen tetroxide-nitric oxide propellant mixtures by Fourier transform proton magnetic resonance spectrometry

Liquid dinitrogen tetroxide, N2O4, and mixed oxides of nitrogen as used as rocket propellant oxidizers, contain the products of the reaction of N2O4 with adventitious water. The determination of the total concentration of water and water-derived species, called the water equivalent content, is essential in view of the effect of the hydrolysis products upon the rate of corrosion of containment metals and the physical state of the corrosion products. High field Fourier transform proton magnetic resonance spectrometry has now been validated for the direct measurement of water equivalent for MON blends up to MON-3, without prior oxidation. Oxidation does, however, give slightly better precision. The technique is shown to be a reliable, absolute method for the determination of water equivalent contents as low as 0.003 wt% and up to at least 0.2 wt%. The precision of the method in this range is within 5%: it is estimated that the water equivalent content could be determined at levels as low as 0.0001 wt%. Samples of N2O4 prepared for NMR analysis are stable in sealed glass tubes for more than 1 year.