溶媒抽出吸光光度法による鉄鋼中微量タングステン定量手順の化学的検証

抄録

Accurate determination of trace tungsten in steel is essential for quality control and process management in steel production. The solvent extraction spectrophotometric method based on the formation of tungsten(V)–thiocyanate complexes with tetraphenylarsonium chloride, specified in Annex 3 of JIS G 1220, has long been used in routine analysis. However, several operational steps in this procedure are based on empirical practices, and their chemical validity has not been sufficiently examined. In this study, critical analytical steps affecting the analytical results were systematically investigated, with particular attention to the sulfuric acid fuming step after sample digestion, reduction of tungsten(VI) by tin(II), temperature control during complex formation, and time management between solvent extraction and absorbance measurement. The procedure examined in this study was applied to certified reference materials of alloy tool steel and high-speed steel, showing good agreement between measured and certified tungsten contents. These results provide a chemical basis for the procedure specified in Annex 3 of JIS G 1220 and support its application in routine tungsten analysis of steel samples.