Determination of trace amounts of gaseous elements (C and O) in high-purity iron

In order to precisely determine trace amounts of carbon (below about 5 mu g/g) and oxygen (below about 5 mu g/g) in a high-purity iron, it is necessary to remove carbon and oxygen adsorbed and combined on the surface of the iron as contamination, and to lower the experimental blank value. When the surface of the iron was polished electrolytically in an ice-cooled mixture of perchloric acid and acetic acid or etched chemically in an ice-cooled mixture of hydrofluoric acid, hydrogen peroxide and distilled water, adsorbed and combined carbon on the surface was removed. Oxygen was almost removed by electrolysis in an ice-cooled mixture of acetic acid and perchloric acid or by coating with 1,10-phenanthroline following chemical etching in hydrochloric acid. By means of these polishing procedures, the precision of determination of carbon and oxygen was improved. The experimental background level of carbon was reduced by pre-heating of a porcelain crucible and an accelerator for combustion of the analytical sample in atmosphere, and similarly the level of oxygen was reduced by heating a graphite crucible in an analytical equipment at high temperature.