アルカリホスファターゼによるp-ニトロフェニルリン酸の加水分解を利用した均一溶液からのコバルト共存下でのリン酸マグネシウムアンモニウムの沈殿生成

田口 茂, 多賀 光彦, 吉田 仁志, 蟇目 清一郎

doi:10.2116/bunsekikagaku.23.193

In the course of precipitation of magnesium ammonium phosphate from homogeneous solution by means of hydrolysis of p-nitrophenylphosphate with an alkaline phosphatase in the presence of cobalt, the behavior of cobalt and the conditions for the quantitative precipitation of magnesium in the presence of cobalt were studied. Precipitates of magnesium ammonium phosphate are contaminated with a considerable amount of cobalt under such conditions that cobalt does not precipitate in the absence of magnesium. When a certain amounts of precipitates of magnesium ammonium phosphate, which was prepared separately, was added to a solution containing cobalt (II) ions, phosphate ions, and ammonia-ammonium chloride, the concentration of cobalt in the mother liquid was decreased after two hours and cobalt phosphates were precipitated on the surface of the magnesium ammonium phosphates. This fact suggests that precipitation of cobalt phosphates is induced by the magnesium salt. When magnesium ammonium phosphates were precipitated from homogeneous solution in the presence of cobalt, two types of contamination with cobalt were observed; contamination due to inclusion of cobalt ion in the lattice of magnesium ammonium phosphate and that due to secondary precipitation of cobalt phosphate on the surface of the magnesium precipitate. The contamination of the first type is not removed easily by digestion of the precipitate in concentrated ammonia-ammonium chloride buffer solution, while the contamination of the second type can be almost removed. The effects of EDTA and potassium cyanide as masking reagent were studied; but both agents prevented quantitative precipitation of the magnesium ammonium phosphate and inhibited the enzyme action. Addition of concentrated ammonia-ammonium chloride buffer solution is very effective to decrease the contamination. Although it inhibits the enzyme action slightly, quantitative precipitation of magnesium ammonium phosphate can be satisfactorily achieved by using a suitable excess amount of the enzyme. The following procedure is recommended for determining 10 mg of magnesium in the presence of less than 10 mg of cobalt. Add 20 ml of ammonia-ammonium chloride buffer solution (pH 9.5), 3 ml of 0.4 M disodium p-nitrophenylphosphate solution, and 6 ml of 0.1 % alkaline phosphatase solution to the sample solution, and dilute to 50 ml with water. Keep the solution at 30°C for more than 8 hours. Filter the precipitate, dry it at 50°C, and weigh as MgNH₄- PO₄·6H₂O. The relative error is less than 0.7%.

アルカリホスファターゼによる<I>p</I>-ニトロフェニルリン酸の加水分解を利用した均一溶液からのコバルト共存下でのリン酸マグネシウムアンモニウムの沈殿生成

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