Determination of Total Potassium in Organic Fertilizers (Agricultural Industry Standard)
1 Subject content and scope of application This standard specifies the sulfuric acid-hydrogen peroxide digestion and flame photometric determination of total potassium of organic fertilizers.
This standard applies to the determination of total potassium in non-mud organic fertilizers.
2 Reference standards
GB/T 6682 Analysis Laboratory Water Specifications and Test Methods
3 Methodology The organic fertilizer sample was digested with sulfuric acid-hydrogen peroxide, diluted and determined by flame photometry. In a certain concentration range, the concentration of potassium in the solution is in direct proportion to the luminescence intensity.
4 The reagents used in the reagents are all of analytical grade except those indicated. Analytical water should meet the specification of the third-grade water in Chapter 5 of GB/T 6682.
4.1 Sulfuric acid (GB/T 625).
4.2 Hydrogen peroxide (GB/T 6684).
4.3 Phosphorus standard stock solution: 1mg/mL
Weigh 1.907 g of potassium chloride (GB 646) that has been dried at 110 °C for 2 hours and dissolved in water to a volume of 1 L. 1 mL of this solution contained potassium (K) 1 mg and was stored in a plastic bottle.
4.4 Potassium standard solution: 100μg/mL
Pipette 10.0mL of potassium (K) standard stock solution (4.3) into a 100mL volumetric flask and add water to volume. This solution contains 1mL potassium (K) 100μg.
5 instruments, equipment, laboratory equipment, and
5.1 analytical balance; the amount of sense is 0.1mg.
5.2 adjustable electric furnace: 1000W.
5.3 Flame photometer.
5.4 Kelvin flask: 50 or 100 mL.
5.5 Volumetric flasks: 50, 100, 1000 mL.
5.6 pipette: 5,10 mL.
5.7 Curved neck small funnel: Φ2cm.
5.8 bottle with a stopper: 150mL.
6 Preparation of sample After taking the air-dried laboratory sample and mixing it thoroughly, it shall be reduced to about 100g by quartering method, crushed, all passed through a 1mm aperture sieve, and then put into a sample bottle for use.
7 Analysis steps
7.1 Preparation of sample solution Weigh out the sample 0.5g (liquid fertilizer such as urine or manure, etc. directly weigh 1~2g liquid), accurate to 0.001g, carefully placed in the bottom of the Kaiser flask (5.4), rinse with a small amount of water The sample attached to the bottle wall was added with 5.0 mL of sulfuric acid (4.1) and 1.5 mL of hydrogen peroxide (4.2), carefully shaken, and a small neck funnel (5, 7) was placed over the bottle and allowed to stand overnight.
Heat on the adjustable electric furnace (5.2), slowly warm up to smoke sulfuric acid, remove, add 15 drops of hydrogen peroxide (4.3) after slightly cold, gently shake the Kaiser flask, heat for about 10min, remove, after a little cold Add 5 to 10 drops of hydrogen peroxide (4.2) in several portions and retort in several portions until the solution is a colorless or pale yellow serum. Continue heating for 10 minutes and remove the remaining hydrogen peroxide. Remove slightly cold, carefully add water to 20 ~ 30mL, heated to boiling. Remove the cooling and rinse the small necked funnel with a small amount of water. The lotion is collected in the original Kaiser flask. The cooking liquid into 100mL volumetric flask, add water to volume, stand still to clarify or use non-phosphorus filter paper in a stoppered flask (5.8) in the spare.
The same experiment was done in two parallel assays.
7.2 blank test In addition to without the sample, the reagents and procedures used are the same as 7.1.
7.3 calibration curve drawn draw potassium standard solution (4.4) 0,2.50,5.00,7.50,10.00mL were placed in five 50mL volumetric flask, add and draw a sample solution equal volume of blank solution, with water to volume, this solution is 1 mL standard solution series containing potassium (K) 0, 5.00, 10.00, 15.00, 20.00 μg. On the flame photometer, adjust the instrument zero point with a blank solution and adjust the full scale to 80 degrees with the highest concentration standard solution in the standard solution series. The other standard solutions were measured from low concentration to high concentration in turn and the instrument indications were recorded. According to the potassium concentration and instrument indications, draw a calibration curve or find a linear regression equation.
7.4 Determination Pipette 5.00mL sample solution (7.1) in a 50mL volumetric flask and add water to the chamber. The same conditions as the standard solution series were measured on a flame photometer and the instrument was recorded. Calibrate the instrument with potassium standard solution after measuring 5 samples.
8 Expression of the analytical results The total potassium (K) content is expressed in g/kg and calculated as follows:
Total potassium (K)
Where: c - obtained from the calibration curve or by the regression equation to determine the color phosphor concentration, μg/mL;
V-coloring volume, 50mL;
D-Distribution multiple, volume volume / volume, 100/50;
m-Weigh the sample mass, g;
10-3- Convert μg/g to a factor of g/kg.
The result should be expressed to two decimal places.
9 Allowable difference
9.1 The arithmetic average of the results of two parallel measurements is taken as the result of the determination.
9.2 The absolute difference allowed by the results of two parallel measurements shall meet the following requirements:
K,g/kg allowable difference,g/kg
<5.0 < 0.5
5.1 to 10.0 <0.7
10.1 to 15.0 <0.9
>15.1 <1.2
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