Trace analysis of small gas samples in sealed containers with mass spectrometry using static dilution

A sampling method for the analysis of small amounts of gases from sealed containers is described. Liquefied pressurised gas samples were expanded into a vacuum box and statically diluted with ultrapure nitrogen. The equations for the sample dilution were established, relating the measured impurity amount fractions in the sample mixture to their partial pressures in the sealed container and, in the case of oxygen, to the air pressure. Ion?Cmolecule reaction mass spectrometry allowed identification and measurement of trace impurities corresponding to partial pressures in the range of 1?hPa in the container. The method was applied for determining the identity and amount of gaseous impurities in n-butane used in implantable gas pressure?Coperated drug infusion pumps. Impurities from the n-butane supply cylinder or from decomposition products, for example due to the laser welding of the Ti plugs of the containers, could be excluded by the results of saturation vapour pressure measurements, FID gas chromatograms and IMR mass spectra. The variability in pressure versus volume among tested infusion pump samples was associated with excess oxygen, attributable to an excessive residual air pressure in the gas containers before they were filled with n-butane. The sample preparation method is principally applicable to measure the composition of small amounts of gas mixtures and gaseous impurities with identified IMR mass spectra down to trace levels??even for ubiquitous substances like oxygen. The volume of the produced gas mixtures allows characterisation of the gas by standard gas analytical methods and for impurities by trace gas analytical methods.