Determination of ultratrace amounts of elements in ultra-high-purity iron, steel, iron-chromium alloy and other alloys by spectrochemical analysis after chemical separation

Recently, ultra-high-purity iron which contained ultratrace amounts of elements as impurity was made. Analytical methods were investigated for the determination of 37 elements as impurities in the iron samples. Trace carbon in the iron was determined by a combustion-infrared absorption method. The combustion of an analytical sample of iron was accelerated by mixing it and a combustion accelerator consisting of tungsten and tin. Because a blank of carbon in the accelerator and a ceramic crucible (or boat) could be removed, it became possible that trace carbon in the iron and carbon adsorbed on the surface of the iron were separately determined. Similarly, a blank of sulfur was decreased for the determination of trace sulfur in iron. For determining trace oxygen, an analytical sample had to be cleaned by chemical etching in acids or electrolytic polishing. Trace amounts of Ag, Au, Se and Te were separated from major elements of an analytical sample by coprecipitation with metallic Pd as a carrier. Trace P and As were coprecipitated with Be(OH)P in an ammonium alkaline solution. This method was applied to the separation of P and As from major elements that were masked by EDTA. Trace V, Hf, Mo, Nb, Ga, Zr and Ti were separated as cupferron complexes. Trace B and Si were separated as gaseous compounds (trimethyl berate and silicon tetrafluoride), respectively. Trace Al, Ba, Bi, Cd, Co, Cr, Cu, Mg, Mn, Ni, Pb, Ti and Zn were separated from iron that was extracted by 4-methyl-2-pentanone. The trace elements were determined by ICP-AES, graphite furnace-AAS and spectrophotometry. The determinable content of each trace element was about 0.1 mug g(-1). Then, an iron sample better than 99.9987% was analyzed.