抽出比色による高ボイラー給水中の超微量シリカの定量
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概要
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Spectrophotometric determination of trace amounts of silica in feed water for high pressure boilers has been investigated following the extraction method developed by W. Sonnenschein.<BR>A number of high molecular weight amines has been tested for the ability of extracting silicomolybdenum-blue from water to chloroform, and polyoxyethylene laurylamine has been found to be most adequate for the purpose.<BR>The recommended analytical procedure is as follows. Acidic molybdate solution is added to 200 m<I>l</I> of sample solution. After being set aside for 15 min., 10% oxalic acid solution is added to it. After 5 min., the reductant solution, prepared just before use, containing formic acid, sodium formate, tin oxalate and sulfuric acid is added to the solution.<BR>The solution is allowed to stand for 10 min. and is transferred to a shaking flask, to which 5 m<I>l</I> of 5% polyoxyethylene laurylamine solution is added. Then the solution is shaken for 3 min. with 10 m<I>l</I> chloroform and extraction is repeated with two successive 6 m<I>l</I> portions of chloroform.<BR>The extract is collected into a 25 m<I>l</I> volumetric flask containing 3 m<I>l</I> methanol and is diluted exactly to the mark with pure chloroform. The absorbance is measured at 750 mμ in a 50 mm cell, using a reference blank on pure chloroform.<BR>Three ppb of silica can be determined, and confidence interval extends from 2.77 ppb to 3.23 ppb at 3 ppb silica concentration in case of 95% confidence coefficient.
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