NY 525-2012Organic fertilizer (English PDF)

5.2.3.6 Phenanthroline indicator

Weigh 0.695 g of ferrous sulfate (analytically pure) and 1.485 g of phenanthroline (analytically pure) to dissolve in 100 mL of water; and shake up as standby. The indicator is perishable, so it shall be sealed and stored in a brown bottle.

5.2.4 Determination procedures

Weigh 0.2 g ~ 0.5 g (accurate to 0.000 1 g) of air-dried sample that has been screened through Mesh Phi 1 mm; place in a 500 mL triangular flask; accurately add 50.0 mL of

0.8 mol/L potassium dichromate solution (5.2.3.4); then add 50.0 mL of concentrated sulfuric acid (5.2.3.2); add a bent neck small funnel; place in boiling water; and maintain for 30 min after water is boiling. Take out and cool to room temperature; use water to rinse the small funnel; and contain the washings into the triangular flask. Take down the triangular flask; transfer the reactant nondestructively into a 250 mL volumetric flask; cool to room temperature; add dropwise to scale; absorb 50.0 mL of the solution to pour into a 250 mL triangular flask; add water approximately to 100 mL;

add 2 drops ~ 3 drops of phenanthroline indicator (5.2.3.6); use 0.2 mol/L ferrous sulfate standard solution (5.2.3.5) to titrate to the end when the solution turns from certain acidity, the phosphate anions in the solution to be tested reacts with metavanadic acid and molybdic acid to generate yellow ternary heteropoly acid. Within a certain concentration range [1 mg/L ~ 20 mg/L], the absorbance and the phosphorus content of the yellow solution are in a direct proportion relationship; and then use the spectrophotometric method to quantify phosphorus.

5.4.2 Reagents

5.4.2.1 Sulfuric acid (rho1.84).

5.4.2.2 Nitric acid.

5.4.2.3 30% hydrogen peroxide.

5.4.2.4 Vanadium ammonium molybdate reagent.

Solution A. weigh 25.0 g of ammonium molybdate to dissolve in 400 mL of water.

Solution B. weigh 1.25 g of ammonium metavanadate to dissolve in 300 mL of boiling water; add 250 mL of nitric acid (5.4.2.2) after cooling; and cool.

Inject solution A slowly into solution B while stirring; use water to dilute to 1 L; mix up;

and store in a brown bottle.

5.4.2.5 Sodium hydroxide solution. a solution of mass concentration 10%.

5.4.2.6 Sulfuric acid (5.4.2.1). a solution of volume fraction 5%.

5.4.2.7 Phosphoric acid solution. 50 µg/mL.

Weigh 0.219 5 g of potassium dihydrogen phosphate (standard reagent) dried for 2 h at 105°C; transfer to a 1 L volumetric flask after using water to dissolve; add 5 mL of sulfuric acid (5.4.2.1); and use water to add to scale after cooling. 1 mL of the solution contains 50 µg of phosphorus (P).

5.4.2.8 2,4-(or 2,6-) dinitrophenol indicator. a solution of mass concentration 0.2%.

5.4.2.9 Non-phosphorus filter paper.

5.4.3 Apparatus

Commonly-used laboratory apparatus and spectrophotometer.

5.4.4 Analytical procedures

5.4.4.1 Preparation of sample solution

Prepare as specified in 5.3.4.1.

5.4.4.2 Preparation of blank solution

5.5.3 Apparatus

Commonly-used laboratory apparatus and flame-photometer.

5.5.4 Analytical procedures

5.5.4.1 Preparation of sample solution

Prepare as in 5.3.4.1.

5.5.4.2 Preparation of blank solution

Except that no sample is added, the reagents used and operation are the same as in

5.4.4.1.

5.5.4.3 Plotting of standard curve

Absorb 0 mL, 1.00 mL, 2.50 mL, 5.00 mL, 7.50 mL and 10.00 mL of potassium standard solution (5.5.2.4) to pour into six 60 mL volumetric flasks respectively; add blank solution of an equal volume to that of sample solution absorbed; and add water to scale.

The solutions are the standard solution series, 1 mL of which contains 0 µg, 2.00 µg,

5.00 µg, 10.00 µg, 15.00 µg and 20.00 µg of potassium (K). On the flame-photometer, use blank solution to adjust the apparatus to zero point and use the standard solution of maximum concentration in the standard solution series to adjust the full scale to 80 scale mark. Then measure other standard solutions in turn from low concentration to high concentration; and record the indicating values of the apparatus. Plot the standard curve or calculate the linear regression equation in accordance with the potassium concentration and apparatus indicating values.

5.5.4.4 Determination

Absorb 5.00 mL of sample solution (5.5.4.1) to pour into a 50 mL volumetric flask; and add water to scale. Carry out determination on a flame-photometer under the same conditions as the standard solution series; and record the apparatus indicating values.

Use potassium standard solution to calibrate the apparatus after testing every 5 samples.

5.5.5 Expression of analysis results

The potassium content of fertilizer is expressed using the mass fraction of fertilizer and calculated in accordance with Equation (5).

where, c3 -- potassium concentration of solution to be determined which is obtained from the standard curve or regression equation, in µg/mL;

phosphate (KH2PO4) dried for 2 h at 120°C and 3.53 g of anhydrous disodium hydrogen phosphate (Na2HPO4) dried for 2 h at 130°C; use water to dissolve; and dilute and add to 1 L.

5.7.3.3 pH 9.18 standard buffer solution. weigh 3.8 g of borax (Na2B4O7·10H2O) (which is balanced for one week in a desiccator containing cane sugar-salt solution);

use water to dissolve; and dilute and add to 1 L.

5.7.4 Operating procedures

Weigh 5.0 g of air-dried sample screened through Mesh Phi 1 mm to place into a 100 mL beaker; add 50 mL of water (boiled to remove carbon dioxide); stir for 15 min; allow to stand for 30 min; and use a pH meter to determine.

5.7.5 Admissible differences

Take the arithmetic mean value of parallel determination results as the final analysis result, rounded off to the first decimal place. The absolute differences between parallel analysis results shall not be greater than 0.2 pH unit.

5.8 Determination of heavy metals

5.8.1 Proceed as specified in GB 18877.

5.8.2 Expression of analysis results

The heavy metal content of fertilizer is expressed using the mass fraction of fertilizer

omega (mg/kg) and calculated in accordance with Equation (6).

where,

rho -- heavy metal concentration of solution to be determined which is obtained from the standard curve or regression equation, in µg/mL;

rho0 -- heavy metal concentration of blank solut...

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