This standard is applicable to the determination of urea nitrogen content in urea or fertilizers containing only nitrogen by urease method. This method is also applicable to corresponding industrial products. GB 3598-1983 Determination of urea nitrogen content in fertilizers Urease method GB3598-1983 standard download decompression password: www.bzxz.net

Scope of application
National Standard of the People's Republic of China
Determination of ureanitrogen content in fertilizers
Urease method
Fertilizers--Determination of ureanitrogen content-urease methodUDC 631.8
：543.06
GB 3598-83
This standard applies to the determination of urea nitrogen content in urea or fertilizers containing only nitrogen by urease method. This method is also applicable to corresponding industrial products.
2 Principle
In a solution of constant acidity, urease is used to convert urea nitrogen into ammonia, which is then titrated with a standard sulfuric acid solution. The reaction formula is as follows: CO (NH2)2+2H2O (NHa)2CO3(NH,)2 CO 3+H,SO 4-(NH), SO+CO2+H,O3 Reagents and solutions
3.1 Bromocresol green (HG3-1220--79): 0.1% ethanol solution. 3.2 Methyl orange (HGB3089--59): 0.1% solution. 3.3 95% ethanol (GB 679--80).
3.4 ​​Mixed indicator solution: 6 parts of 0.1% bromocresol green solution (3.1) and 1 part of 0.1% methyl orange solution (3.2) are mixed. 3.5 Sulfuric acid (GB 625-77).
3.6 0.5N sulfuric acid standard solution: Prepare and calibrate according to GB601-77 "Preparation Method of Chemical Reagent Standard Solution". 3.7 Urease: fresh 1% solution (suspension). 4 Apparatus
4.1 pHt.
4.2 Water bath.
5 Determination procedure
5.1 Preparation of test solution
Weigh 5 g of the sample, accurate to 0.0002 g, place it in a beaker, add water to dissolve, transfer to a 500 ml volumetric flask, dilute to the mark, and mix well. www.bzxz.net
5.2 Titration
Pipette V ml of test solution (containing 0.20-0.25 g urea equivalent), transfer to a beaker, dilute to 100 ml, and titrate with 0.5 N sulfuric acid standard solution (3.6) to pH 4.2 [measured with a pH meter (4.1)); or add 4 drops of mixed indicator solution (3.4), and titrate with 0.5 N sulfuric acid standard solution (3.6) until the solution turns grayish green (pH 4.2) as the end point, and record the required amount. Pipette √ ml of test solution, transfer to a 250 ml conical flask with a ground stopper, dilute to 100 ml, add the required amount for the above titration. National Bureau of Standards Issued on April 11, 1983
Implementation on February 1, 1984
GB 3598-83
Add 25 ml of 1% urease solution (3.7) to the volume of 0.5N sulfuric acid standard solution (3.6), plug the bottle tightly, shake vigorously for 2 minutes, let it stand at 25±2℃ for 1 hour [or let it stand in a 40±2℃ water bath (4.2) for 30 minutes and cool to room temperature], rinse the bottle stopper and bottle wall with water, and then titrate with 0.5N sulfuric acid standard solution (3.6). At the beginning, quickly add 15 ml, and then continue to titrate until the pH is close to 4.2. Transfer the solution quantitatively into a beaker (the total volume of the solution is not more than 200 ml), and at the pH value (4.1), titrate to pH 4.2 as the end point; or after quickly adding 15 ml of 0.5N sulfuric acid standard solution (3.6), add 4 drops of mixed indicator solution (3.4) and continue to titrate until the solution turns gray-green (pH is 4.2) as the end point. 5.3 Blank test
Carry out a blank test according to the above procedure.
6 Expression of results
6.1 Calculation
6.1.1 The percentage of urea nitrogen content (on a dry basis) is calculated as follows: N (V × 0.01401 × 100 =
N (V-±,) × 500×140.1
G×100-X,
Wherein: N
equivalent concentration of sulfuric acid standard solution,
volume of sulfuric acid standard solution used for titration of sample, milliliter; volume of sulfuric acid standard solution used for blank test, milliliter; volume of test solution absorbed, milliliter,
mass of sample, gram,
moisture content of a sample,
mass of each milligram equivalent nitrogen, gram.
6.2 Allowable error
6.2.1 The arithmetic mean of the parallel determination results shall be taken as the determination result. 6.2.2 The absolute difference of the parallel determination results shall not exceed 0.10%. 6.2.3 The absolute difference of the determination results of different laboratories shall not exceed 0.15%. G×V (100 - X)
GB 3598—83
Appendix A
General description of this standard
(Supplement)
A.1 Measuring instruments used in the standard, such as balances, scales, volumetric flasks, burettes, pipettes, etc., should be calibrated before use. A.2 Water used in the standard, unless otherwise specified, is distilled water or deionized water. A.3 Reagents used in the standard, unless otherwise specified, are all chemically pure or above. A.4 Acid or ammonia liquid reagents used in the standard, when only the reagent name is written, refer to reagents with the concentration specified in the reagent standard (i.e., concentrated acid or concentrated ammonia). For example, sulfuric acid refers to 95-98% sulfuric acid, and ammonia refers to 25-28% ammonia. A.5 When aqueous solutions prepared with liquid reagents in the standard are expressed as the volume of the reagent plus the volume of water, for example, 1+3 sulfuric acid refers to 1 volume of sulfuric acid and 3 volumes of water.
A.6 Percent concentration solutions prepared with solid reagents in the standard refer to The number of grams of solute contained in 100 ml of solution. A.7 The instruments or reagents and solutions mentioned in the determination procedure in the standard shall use the specifications specified in the instruments or reagents and solutions. A.8 For the blank test, except that no sample is added, the operating procedures, applied reagents and reagent dosage are the same as those in the determination. Additional remarks:
This standard is formulated with reference to the European Economic Community's uniform regulations on fertilizer sampling and analysis methods (1977), the fertilizer sampling and analysis methods formulated by the Quality Committee of the American Fertilizer Association (1974), and JOACVo1.59No.5P1045-1048 (1976) and other relevant materials.
This standard was proposed by the Ministry of Chemical Industry of the People's Republic of China and is under the jurisdiction of the Shanghai Research Institute of Chemical Industry of the Ministry of Chemical Industry. The Shanghai Research Institute of Chemical Industry of the Ministry of Chemical Industry and the Fertilizer Research Institute of the Ministry of Chemical Industry are responsible for drafting this standard. The main drafters of this standard are Zhao Yuwei and Xu Dejiao. 6
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