The determination of nitrogen in metals by isotope dilution

A wet chemical procedure for determining the amount of nitrogen in a metal or alloy has been developed which utilizes the isotope dilution technique. Ammonium sulfate, either enriched or depleted in ¹⁵N, is added to the metal sample during solution procedures. Ammonium ions resulting from the hydrolysis of bound nitrogen in the metals mix with that of the tracer and the total is then oxidized to N₂ in which form the element is analyzed in the mass spectrometer. The method has been tested on a variety of metals and alloys including thorium, lanthanum, yttrium, titanium, chromium, manganese, various steels, nickel-chromium, ferrotitaniuin, ferromanganese and ferrochromium. The range of nitrogen in these materials was from -2 ppm to almost 6%. Average precision was generally better than ± 5%.