The suitability of a mass spectrometer for vacuum fusion analysis is discussed; the equipment and its mode of operation and calibration are described. The objections to using an oil pump for extracting the gases liberated from the metal samples have been overcome with this apparatus.Results for oxygen determination in steels, molybdenum and zirconium have been independently checked by using a fast neutron-activation technique, and the results of two methods are shown to be in good agreement.Oxygen levels of 116 p.p.m. have a standard deviation of 6 p.p.m. and coefficient of variation of 5 per cent. Although most of the work has been carried out on oxygen determinations, nitrogen results are quoted for two standard iron samples showing that the method is also acceptable for nitrogen determinations. Kitrogen levels of 31 p.p.m. have a standard deviation of 3 p.p.m. and a coefficient of variation of 10 per cent.The limits of detection for the equipment are 0.1 p g of oxygen, 0.1 ,ug of nitrogen and 0.01 p g of hydrogen.VACGUM fusion analysis is a well known method for the determination of oxygen, nitrogen and hydrogen in metals, and a comprehensive, up-to-date review of the literature has been given by James.l Most papers, however, describe equipment capable of determining oxygen down to 10 p.p.m. This is no longer adequate as the metallurgical requirements for metals sucl as copper, molybdenum, tantalum and tungsten may be below this level; for example, coppir that is to be used in vacuum devices is required to have an oxygen content of less than 0.5 p.p.m. The detection limit of some equipments could be lowered by increasing the sample weights, but large samples are not always available, and an equipment capable of determining gas contents on small samples, in particular oxygen contents below 10 p.p.m., was required. Techniques for the analysis of small amounts of gas were considered, such as gas chromatography and mass spectrometry, and mass spectrometry was thought to be most suitable for vacuum fusion analysis.Mass spectrometers have been used by Taylor2 for the analysis of gas obtained by vacuum fusion; in this method the gas was collected in a bottle and then transferred to the spectrometer. Martin et aL3 used a mass spectrometer directly coupled to their vacuum fusion equipment. This equipment, however, required large sample weights, 6 to 14 g, and blanks had to be carried out for 1 hour so that sufficient blank gas was present for analysis.The object of the work described in this paper was to produce an equipment suitable for routine analysis of materials with high gas contents, and in particular capable of analysing material with low gas contents for specialised purposes.
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