This standard specifies the determination of potassium content in compound fertilizers. This standard is applicable to the determination of potassium content in compound fertilizers. GB/T 8574-2002 Determination of potassium content in compound fertilizers Potassium tetraphenylborate gravimetric method GB/T8574-2002 Standard download decompression password: www.bzxz.net

1 Scope
Determination of potassium content in compound fertilizers
Potassium tetraphenylborate gravimetric methodWww.bzxZ.net
This standard specifies the determination of potassium content in compound fertilizers. It is applicable to the determination of potassium content in compound fertilizers. ? Normative references
GB/T8574—2002
The clauses in the following documents become the clauses of this standard through reference in this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, the parties to the agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version shall apply to this standard. GB/T8571 Preparation of laboratory samples for compound fertilizers HG/T2843 Common standard titration solutions, standard solutions, reagent solutions and indicator solutions for chemical analysis of fertilizer products 3 Principle
In a weakly alkaline medium, use sodium tetraphenylborate solution to precipitate potassium ions in the sample solution, filter the precipitate, dry it and weigh it. If the sample contains hydrides or organic matter, bromine water and activated carbon can be added first for treatment. In order to prevent cationic interference, an appropriate amount of disodium ethylenediaminetetraacetic acid (EDTA) can be added in advance to complex the cations with disodium ethylenediaminetetraacetic acid. 4 Reagents and materials
4.1 The preparation of reagents, water and liquid used in this standard shall comply with the provisions of HGT2843 when the specifications and preparation methods are not specified. 4.2 Sodium tetraphenylborate solution: 15g/L
Ethylaminetetraacetic acid disodium salt (EDTA) solution: 40g/L4.4
Sodium hydroxide solution: 400g/L-
Mass fraction of bromine aqueous solution: about 5%
Sodium tetraphenylborate washing solution: 1.5g/L
Phenolic acid: 5g/L ethanol solution, dissolve 0.5g phenolic acid in 100mL 95% (mass fraction) ethanol: Activated carbon: It should not adsorb or release potassium ions. 5 Instruments
5.1 Bandpass laboratory instruments:
5.2 Glass filter: No. 4, 30ml
5.3 Drying oven: capable of maintaining a temperature of 120C5C. 6 Preparation of sample solution
Prepare laboratory samples according to GB/T8571. Weigh 2g~5g of sample containing about 400mg of potassium oxide (accurate to 0.0002g), place in a 250ml conical flask, add about 150ml GB/T85742002
water, heat and boil for 30min, cool, quantitatively transfer to a 250mL volumetric flask, dilute with water to the mark, mix, dry filter, discard the first 50mL filtrate,
7 Analysis steps| |tt||7.1 Test solution treatment
7.1.1 The sample does not contain amine compounds or organic matter. Take 25mL of the above filtrate and put it in a 200mL beaker. Add 20mL of EDTA solution (40mL can be added when it contains more cations) and 2-3 drops of phenol solution. Add sodium hydroxide solution until red appears, then add 1mL in excess. Heat slowly in a well-ventilated cabinet and rinse for 15 minutes. Then let it cool or cool it to room temperature with running water. If the red color disappears, add sodium hydroxide solution to adjust it to red. 7.1.2 The sample contains cyanamide or organic matter. Take 25mL of the above filtrate and place it in a 200mL~250mL beaker, add 5mL of bromine solution and boil the solution until all the cyanamide is completely removed (no color). If it contains other colors, evaporate the liquid volume to less than 100mL. After the liquid is cooled, add 0.5 activated carbon and stir it thoroughly to adsorb it, then filter and wash 3~5 times, using about 5mL of water each time to collect all the filtrate: add 20mL of EDTA liquid (add 40mL when it contains more cations). The procedure is the same as (7.1.1D). 7.2 Precipitation and Filtration
While stirring, add sodium tetraphenylborate solution dropwise to the sample solution (7.1:1 or 7.1.2). The amount added is 0.5mL of sodium tetraphenylborate solution per 1M potassium oxide and an excess of about 7mL. Continue stirring for 1min. Let it stand for more than 15min. Filter the precipitate by decantation into a No. 4 glass crucible filter that has been pre-weighed at 120°C. Wash the precipitate 5 to 7 times with sodium tetraphenylborate washing solution, using about 5mL each time. Finally, wash it twice with water, each time The amount used for the second time is 5mL. 7.3 Drying
Put the solution containing the precipitate in a 120°C ± 5°C drying oven, dry for 1-5 minutes, then cool it in a desiccator and weigh it. Note: When washing with dry air, if the precipitate is difficult to wash off, it can be further washed with an inner jar. 7.4 Blank test
Except for not adding the test solution, the analysis steps and the amount of reagents are the same as the above steps. Expression of analysis results
Potassium (in KO) content is expressed as mass fraction W(K,O) and calculated according to formula (1): W(K.0)-(m2m)×0.1314 ×100=9m-m）x131.4
Wherein:
The mass of the precipitate obtained from the test solution, in grams (g)The mass of the precipitate obtained during the blank test, in grams (g)0.1314
The coefficient for converting the mass of potassium tetraphenylborate to the mass of potassium oxide:The mass of the test material, in grams ():
25-The volume of the sample solution absorbed, in milliliters (mL):250-The total volume of the sample solution. In milliliters (m)Take the arithmetic mean of the parallel determination results as the determination result. Allowable difference
The allowable difference of the parallel determination and the determination results of different laboratories shall meet the requirements of Table 1! .1)
Mass fraction of lithium (in terms of K-0/%
10.0~20.0
Allowable difference between parallel determinations/%
GB/T8574-2002
Allowable difference between determinations in different laboratories/%
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