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In the colorimetric determination of phosphate by ALLEN's method, sulfuric acid was used in place of perchloric acid with satisfactory results, Concentrations and dosages of reagents and other experimental conditions were examined in detail and slight modifications were made. 2. The proposed modification is as follows In a 15ml. volumetric flask, 1. 5ml. of 15 vol. % H2SO4, 2. 0ml. of amidol reagent (0. 3g. of amidol and 6. 0g. of NaHSO3 are made up to 100ml. ) and 1. 0ml. of 5% ammonium molybdate solution are mixed with appropriate amount of phosphate solution and made up to the mark with distilled water. Colorimetric readings are made with PULFRICH's step photometer (Carl Zeiss) fitted with filter S 72 after standing for 20_? ? ₄0 minutes at 20_? ? ₃0°C. Total phosphate may be determined after digesting the sample with sulfuric acid and 30% hydrogen peroxide, followed by the addition of amidol and molybdate reagents with distilled water up to 15ml.
Michinori NAKAMURA (Sun,) studied this question.