Colorimetric determination of available silicate in soil extracted by acetate buffer with ascorbic acid powder
1996
Yanai, M. (Fujihira Industry Co. Ltd., Tsukuba, Ibaraki (Japan)) | Yoshida, Y. | Shimizu, Y.
A colorimetric method with ascorbic acid powder and a mixed solution (ammonium molybdate-hydrochloric acid) was developed to determine the acetate buffer-soluble silicic acid content in soil testing. This method is superior to the Imaizumi, Yosida method in terms of stability of color and high sensitivity, and moreover the calibration curve is linear up to 75 mg L(-1) of SiO2. (1) the newly developed analytical procedure is as follows. Place 0.5 Ml of sample solution in a test tube. Add 4.5 mL of distilled water and 0.5 mL of the mixed solution, and allow the mixture to stand for 20 min. Then add 0.5 mL of 400 g L(-1) tartaric acid solution and allow the tube to stand for 3 min. Add one spoonful (45 mg) of ascorbic acid powder with a small spoonful of Zen-Noh reagent. Measure absorbance at 810 nm between 5 min and 5 h later. (2) Maximum concentrations of phosphoric acid, ferrous iron and ferric ironic the extracts of 48 soil samples were 41 mg L(-1) of P2O5, 2.9 mg L(-1) of Fe(2+), and 86 mg L(-1) of Fe(3+), respectively. Therefore no interference by these ions was observed in this method. Low coefficients of variation of from 2% to 4% were obtained in 12 replicate determinations using this method. (3) The contents of acetate buffer-soluble silicic acid determined using this method agreed well with those determined using the ICP method. In this method, high calcium contents in soil samples did not interfere with the determination of the available silicic acid content
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