Water-soluble fertilizers - Determination of humic-acids content
1 Scope
This standard specifies the test method of oxidation-reduction titration after acid precipitation for determination of humic-acids content in water-soluble fertilizers.
This standard is applicable to the determination of humic-acids content in liquid or solid water-soluble fertilizers.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values
HG/T 2843 Chemical fertilizer products - Standard volumetric, standard, reagent and indicator solutions for chemical analysis
NY/T 887 Liquid fertilizers - Determination of density
3 Principle
Humic acid in the sample solution is quantitatively precipitated under acidic conditions, and other substances that interfere with the determination, such as non-humic acid carbon, chloride ions and low-valence metal ions, remain in the solution. After the solution is discarded, the organic carbon in the precipitate is oxidized with quantitative potassium dichromate-sulfuric acid solution, and the remaining potassium dichromate is titrated with ferrous sulfate standard titration solution. The organic carbon content is calculated based on the reagent blank and the oxidant consumption before and after sample oxidation, and the humic-acids content of sample is obtained through conversion of carbon ratio.
