This standard specifies the method of using dioxane to extract free water in fertilizers and then using Karl Fischer reagent to titrate the free water content in compound fertilizers. GB/T 8577-2002 Determination of free water content in compound fertilizers Karl Fischer method GB/T8577-2002 Standard download decompression password: www.bzxz.net

1 Scope
Determination of free water content in compound fertilizers
Karl Fischer method
GB/T8577-2002
This standard specifies the method of obtaining free water in compound fertilizers with dioxane and then titrating with Karl Fischer reagent to determine the free water content in compound fertilizers.
Normative references
The clauses in the following documents become the clauses of this standard through the reference of this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, the parties to an 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/T2441.3 Determination of urea Determination of moisture content Karl Fischer method GB/T6283 Determination of moisture content in chemical products Karl Fischer method (general method) (eg VISO760) GB/T8571
Laboratory sample preparation for compound fertilizers
HG/T2843 Common standard titration solutions, standard solutions, reagent solutions and indicator solutions for chemical analysis of fertilizer products 3 Principle
The free water in the sample reacts quantitatively with the Karl Fischer reagent of known water titer. The reaction formula is as follows! H,O+1,+SO,+3CHN=2CHN.HI+CHN.SOC.HN.SO,+CH.OH-CHNH.OSO,OCH4 Reagents
4-1 The reagents, solutions and water used in this standard shall comply with the provisions of HG/T2843 when the specifications and preparation methods are not specified. 4.25A molecular sieve: 3mm~5mm diameter particles, used as desiccant, before use, roast at 500℃ for 2h and cool in a dryer containing molecular sieve. Used molecular sieve can be washed with water, dried, roasted and regenerated for use: 4.3 Methanol: water content ≤0.05% by mass, if the water content of the reagent is >0.05% by mass, add about 50g of 5A molecular sieve (4.1) to 500mL methanol, plug the bottle, leave it overnight, and absorb the supernatant for use: 4.4 Dioxane: after dehydration, the method is the same as 4.3; 4.5 Anhydrous ethanol: after dehydration, the method is the same as 4.3; 4.6 Karl Fischer reagent: prepared according to GB6283. Note: Karl Fischer modified reagent without pyridine can also be used. Its preparation method is shown in HG/T28435 Instrumentbzxz.net
Karl Fischer direct coulometric titration instrument is equipped according to GB/T6283. 6 Analysis steps
6-1 Calibration of Karl Fischer reagent
GB/T8577-2002
According to the provisions of GB/T6283, calibrate with sodium tartrate dihydrate (or water). 6-2 Determination
Prepare laboratory samples according to the provisions of GB/T8571. In a 125mL conical flask with a rubber stopper of a saline bottle, accurately weigh 1.5g to 2.5g of laboratory sample with a free water content of no more than 150mg, weigh to 0.0001g, cover the bottle stopper, inject 50.0mL of dioxane (except for arbitration, in general, it can be replaced by anhydrous ethanol or methanol), shake or oscillate for several minutes, let it stand for 15 minutes, shake or oscillate for several minutes, and after the sample settles slightly, take part of the solution and centrifuge it in a centrifuge tube with a rubber stopper of a saline bottle. Drain the residual liquid in the titration container through the discharge nozzle, add 50mL of methanol into the titration container. The amount of methanol must be enough to submerge the electrodes. Turn on the power supply and turn on the electromagnetic stirrer. As with the calibration of Karl Fischer reagent, titrate with Karl Fischer reagent until the ammeter produces the same deflection as during calibration, and keep it stable for 1 minute.
Use a syringe to take out 10.0 mL of dioxane extract from the centrifuge tube, inject it into the titration container through the feeding port, titrate to the end point with Karl Fischer reagent, and record the volume of Karl Fischer reagent consumed (). When dioxane is used as the extractant, the residual liquid in the titration container should be completely titrated with methanol after three titrations, and titrate to the same end point with Karl Fischer reagent. Then the next determination is carried out in the same way. The volume (V) of Karl Fischer reagent consumed by 10.0 mL of dioxane is determined. 7. Calculation and expression of analysis results
7.1 Calculation of analysis results
The free hydration content in the sample is expressed as mass fraction W (free water) %). It is calculated according to formula (1): W (free water)
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The volume of Karl Fischer reagent consumed by 10-0 mL of dioxane solution is in liters (mL): The volume of Karl Fischer reagent consumed to determine 10.0 ml of dioxane is in milliliters (ml). The full tolerance of Karl Fischer reagent to water is in grams per milliliter (mg/ml). The mass unit of the test sample is grams (g).
Take the arithmetic mean of the parallel determination results as the determination result. 7.2 Allowable tolerance
When the mass fraction of free water W (free water) is 2.0%, the absolute difference of the parallel determination results should be ≤0.30%: When the mass fraction of free water W (free water) is >2.0%, the absolute difference of the parallel determination results should be 0.40%: Maximum
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