グリオキザール・ビス(2-ヒドロキシアニル)によるカルシウムの抽出比色定量

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Glyoxal-bis(2-hydroxyanil) (GHA) forms a redcolored chelate with calcium ion in an alkaline solution. Because of superiority in selectivity of the reaction for calcium, many papers on spectrophotometric determination of calcium with GHA have been reported, but the disadvantage of the GHA method was that the reagent and its calcium chelate are considerably unstable in the alkaline aqueous solution. To overcome the instability, the color development in a mixture of water and alcohol or extraction of the chelate into a mixture of alcohol and chloroform was tried, all the attempts, however, were not always satisfactory. In this paper, good color-stability has been achieved by extraction of the chelate into 1, 2-dichloroethane with an addition of zephiramine. The recommended procedure is as follows : To a 20-ml sample solution containing calcium less than 1.25μ moles add 2 ml of borate buffer (a mixture of 0.1 M sodium hydroxide and 0.1 M sodium borate solution, pH 12.8) and 3 ml of 5 × 10-3 M GHA ethanol solution in that order in a 100-mlseparatory funnel. After 1 min, add 1 ml of 5 × 10-3 M zephiramine solution and 20 ml of 1, 2-dichloroethane, and shake the solution for 1 min. Separate the organic phase and desciccate it with anhydrous sodium sulfate. Measure the absorbance at 530 mμ against water as a reference. The absorption spectrum of calcium-GHA chelate extracted into 1, 2-dichloroethane shows an absorption maximum at 530 mμ where the reagent blank has no absorption against water. Beer's law is held up to 1.25μmoles of calcium in the 20-ml extract and the molar absorption coefficient is 1.3 × 104. The extracted chelate is very stable and no change in the absorbance is observed for at least 6 hours (Fig. 2). The experiments showed that a constant absorbance was obtained in the ranges 12.713.0 of pH (Fig. 1), 15 min of the shaking time (Fig. 3) and 12 min in the time between the addition of GHA and the extraction (Fig. 4). Variations from 1.3 to 2.0 M in alcohol concentration (Fig. 5), (48)10-4 M in GHA (Fig. 6), and (13)10-4 M in zephiramine (Fig. 7) also showed the same absorbance. It is emphasized that the color-instability of calcium-GHA chelate is completely eliminated by extraction of the chelate into 1, 2-dichloroethane in the presence of zephiramine. The effect of zephiramine on the extraction will be discussed elsewhere.
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グリオキザール・ビス(2-ヒドロキシアニル)によるカルシウムの抽出比色定量

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