溶媒抽出-直流ポーラログラフ法によるリン酸の間接定量

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A system of water and isobutyl alcohol giving two phases can be homogenized to a single phase by adding a much less amount of perchloric acid than sulfuric acid. Molybdate ion and phosphomolybdate complex both provide the same maximum wave at about + 0.2 V vs. S. C. E. in a supporting electrolyte composed of 0.5 M perchloric acid-ca. 0.2 M hydrogen peroxide-ca. 0.8 M isobutyl alcohol. The height of the maximum is proportional to the concentration of molybdenum less than 2 × 10-5 M, and phosphate ion can be determined after the extraction of the complex by isobutyl alcohol. The lower limit of detection or determination is about 3 × 10-7 M phosphorus. For steels containing less than 0.03% phosphorus, 0.1 g of the sample is taken and dissolved with nitric acid. The phosphorus is oxidized to orthophosphate with potassium permanganate and arsenic is eliminated with sulfuric acid and potassium bromide. The solution is diluted to exactly 200 ml in which the final concentration of sulfuric acid should be about 0.75 N. A 10m l aliquot of this solution is transferred into a separatory funnel and after adding 1 m l of ammonium molybdate solution (ca. 5%) the phosphomolybdate complex is extracted with 10m l of isobutyl alcohol. A 2m l aliquot of the extract washed four times with 5m l of 0.5 N sulfuric acid is taken exactly into a 25 ml volumetric flask and filled up to the mark with 1.4m l of perchloric acid (60%), 5 ml of hydrogen peroxide solution (ca. 3%) and water. The polarogram is recorded using this solution and the height of maximum wave is measured. Small amounts of vanadium (V) and tungsten (VI) do not interfere.
社団法人日本分析化学会の論文

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浅岡博
一橋大学商品学教室

溶媒抽出-直流ポーラログラフ法によるリン酸の間接定量

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