Spectrophotometric determination of traces of sulfur in graphite after wet oxidation decomposition

• Published in: BUNSEKI KAGAKU Vol. 35; no. 11; pp. 916 - 919
• Main Authors: HASHITANI, Hiroshi, IZAWA, Kimie, YOSHIDA, Hideyo, ADACHI, Takeo
• Format: Journal Article
• Language: English; Japanese
• Published: Tokyo The Japan Society for Analytical Chemistry 1986; Japan Science and Technology Agency
• Subjects: determination of sulfur in graphite; spectrophotometric determination of sulfur as Ethylene Blue; wet oxidation decomposition of graphite
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.35.11_916

In order to determine traces of sulfur in graphite accurately, a wet oxidation decomposition method has been developed. Sulfur is finally determined spectrophotometrically as Ethylene Blue. Graphite is decomposed through oxidation with periodate in fuming perchloric acid. One gram of graphite powder was completely decomposed in 3 h. The established method includes: decomposition of graphite (less than 2g) in 20ml of perchloric acid containing 0.5g of iodine at 200°C; recovery of iodine with hydrogen peroxide; evaporation of excess perchloric acid; reduction of sulfate with a reductant; distillation of sulfur as sulfide, color development with N, N-diethyl-p-phenylenediamine (DEPD) in presence of iron (III); and measurement of the absorbance of the colored solution at 670 nm. Stability of the standard sulfur solution, effect of pH on the color development, and amounts of DEPD and iron (III) were examined. By the established method, 23 block samples taken from 11 brand graphite materials were analysed. Refined graphite contained less than 10ppm of sulfur, and unpurified graphite 3 to 90 ppm, depending on the raw materials. The segregation of sulfur in a graphite block was generally not so much, compared with that of metal impurities. It was also found that about 90% of sulfur in graphite was leached into fuming perchloric acid, in comparison with the wet oxidation decomposition method.