ポーラログラフ法による試薬食塩およびカセイアルカリ中の微量鉄の定量

概要

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Trace of iron in reagent grade sodium chloride and caustic alkali was coprecipitated by aluminium hydroxide and determined by polarography. According to polarographic study of pottasium hydroxide-mannit supporting electrolyte, we decided the follow conditions: drop time of about 7 sec greater, concentrations of 2 M potassium hydroxide and 0.1 M mannit. The limitting currents of the 1st and the 2nd wave were diffusion controlled; the slopes of the wave were 83 and 54 mV respectively, and the 1 st wave was used for the determination. In order to examine the percentage of the coprecipitation of iron, 25125 γ of iron was coprecipitated from about 200 ml of 30 % aqueous sodium chloride solution with 8 mg of aluminium, dissolved with nitric acid and concentrated ; the residue was then mixed with supporting electrolyte and the polarogram was recorded. The result showed that the percentage of the coprecipitation of iron was about 97 %. The half wave potentials of many metal icns in this supporting electrolyte were measured. They are nearly the same in alkali medium and do not interfere with the 1 st wave of iron. The quantitative determination of iron was made on sodium chloride, pottassium hydroxide, sodium hydroxide and sodium carbonate.
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