水中のppbオーダーの鉄の溶媒抽出 原子吸光定量法
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概要
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A solvent extraction-atomic absorption spectrophotometry for the determination of trace amount of iron has been established. Various extraction methods of iron using such reagents as cupferron, acetylacetone, ammonium pyrollidine dithiocarbamate, sodium diethyldithiocarbamate, oxine and sodium benzoate, were compared and the oxine-methyl-iso-butylketone (MIBK) extraction system was adopted. Trace amount of iron is extracted as its oxinate from large amount of aqueous layer buffered by acetic acidsodium acetate into small amount of MIBK layer, and determined by the atomic absorption method, using an air-acetylene flame. Linear calibration curves were obtained within the concentration ranges of 100500, 20100 and 1050 ppb of iron, when the extractions were carried out with 100, 500 and 1000 m<I>l</I> of aqueous and 10, 20 and 30 m<I>l</I> of organic layers respectively. In the last case, the sensitivity of the method was 0.36 ppb of Fe in the aqueous layer for 1% absorption. The sensitivity of various iron lines were compared by spraying oxine-MIBK extracts obtained from 500 m<I>l</I> of aqueous layer containing 50 ppb of iron, and 2483 Å was selected as the most sensitive line.<BR>Optimum concentration of oxine in the organi clayer was found to be 10<SUP>-3</SUP> <I>M</I>. Large amount of excess oxine in the organic layer decreased the absorbancy of iron. The same phenomenon of decreasing of absorbancy were observed when other kind of organic compounds was dissolved in the extract. Effect of various substances on the iron determination was examined. No serious interference was observed when the extraction was carried out in the presence of 100 ppm of Ca (II), 50 ppm of Mg(II), 1 ppm of Cu(II), Zn (II), Pb (II) Mn (II), Al (III), Si (IV) or 150 ppm of Cl<SUP>-</SUP>. The interference of phosphate was relatively large but it was eliminated by using 10<SUP>-1</SUP> <I>M</I> oxine-MIBK solution as an extracting solvent.<BR>The proposed method was applied to the determination of 50 ppb of iron in the model sample waters. Good recovery was obtained using 10<SUP>-3</SUP> <I>M</I> and 10<SUP>-1</SUP> <I>M</I> oxine-MIBK solutions. Then, the iron amount in several underground water and tap waters were determined by the proposed method. Good agreement was observed between the results obtained by the proposed method and the colorimetric method using 1, 10-phenanthroline as a reagent.