GB/T 8572-2001 Determination of total nitrogen content in compound fertilizers - Titration after distillation
Some standard content:
GB/T 8572.--2001
This standard is a revision of GB/T 8572-1988 "Determination of total nitrogen content in compound fertilizers - Titration after distillation". This standard is not equivalent to the international standard ISO5315:1984 "Determination of total nitrogen content in fertilizers - Titration after distillation". The main differences between this standard and ISO5315:1984 are: the reduction method of nitrate nitrogen in the absence of amide nitrogen is changed from chromium powder to nitrogen alloy; 2 the concentration of sodium hydroxide standard titration solution is changed from 0.1mol/L to 0.5mol/L. Compared with the previous version:
This standard reduces the pollution of heavy metal chromium to the environment; 1
2 the operation process is simpler.
This standard replaces GB/T8572-1988 from the date of publication. This standard is proposed by the State Administration of Petroleum and Chemical Industry. This standard is under the jurisdiction and interpretation of the National Technical Committee for Standardization of Fertilizers and Soil Conditioners. This standard was drafted by: National Fertilizer Quality Supervision and Inspection Center (Shanghai). The main drafters of this standard are: Zhang Xiaoqin, Zhang Minghong, and Zhu Tao. 116
GB/T8572—2001
ISOForeword
ISO (International Organization for Standardization) is a worldwide federation of international standards institutes (ISO member bodies). ISO technical committees are responsible for the formulation of international standards. A member body can organize the formulation of standards on behalf of the technical committee, and international organizations, governments, and non-governmental organizations that have a cooperative relationship with ISO can also participate.
The draft international standard adopted by the technical committee must be approved by the member body before it can be confirmed as an international standard by the ISO committee. This standard was prepared by Technical Committee ISO/TC 134 Fertilizers and soil conditioners and was issued to member bodies in March 1978. The following member bodies voted in favor:
Australia, Brazil, Canada, Czechoslovakia, Egypt, France, Germany FR,, Hungary, India, Iran, Ireland, Israel, Italy, Kenya, Mexico, Netherlands, New Zealand, Norway, Philippines, Poland, Portugal, Romania, South Africa, Spain, Thailand, Turkey, United Kingdom, Soviet Union, Venezuela, Yugoslavia. No member body voted against.
1 Scope
National Standard of the People's Republic of China
Determination of total nitrogen content for compound fertilizers-Titrimetric method after distillation
Determination of total nitrogen content for compound fertilizers-Titrimetric method after distillation This standard specifies the method for the determination of total nitrogen content in compound fertilizers. GB/T 8572—2001
neq ISO 5315:1984
Replaces GB/T8572--1988
This standard does not apply to compound fertilizers containing more than 7% organic matter (except urea and cyanamide compounds). 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T2441.1—2001 Determination method of urea Determination of total nitrogen content GB/T8571--1988 Laboratory sample preparation for compound fertilizers HG/T2843-1997 Commonly used standard titration solutions, standard solutions, reagent solutions and indicator solutions in chemical analysis of fertilizer products 3 Principle
Reducing nitrate with nitrogen alloy in alkaline medium, directly distilling ammonia or reducing nitrate to ammonium salt in acidic medium, digesting with concentrated sulfuric acid in the presence of mixed catalyst, converting organic nitrogen or amide nitrogen and cyanamide nitrogen into ammonium salt, and distilling ammonia from alkaline solution. Absorb ammonia in excess sulfuric acid solution, back titrate with sodium hydroxide standard titration solution in the presence of methyl red-methylene blue mixed indicator. 4 Reagents
The reagents and water used in this standard shall comply with the requirements of HG/T2843 when the preparation method and specifications are not specified. 4.1 Sulfuric acid;
4.2 Hydrochloric acid;
4.3 Chromium powder: fineness less than 250μm;
4.4 Nitrogen alloy (Cu: 50%, Al: 45%, Zn: 5%): fineness less than 850μm;4.5 Potassium sulfate;
4.6 Copper sulfate pentahydrate;
4.7 Preparation of mixed catalyst: fully mix 1000g potassium sulfate and 50g copper sulfate pentahydrate, and grind finely;4.8 Sodium hydroxide solution: 400g/1.;
4.9 Standard titration solution of sodium hydroxide: c(NaOH)=0.5mol/L; 4.10 Sulfuric acid solution: c(1/2HzSO,)=0.5mol/L or c(1/2H,SO,)=1mol/L; 4.11 Methyl red-methylene blue mixed indicator; Approved by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China on July 26, 2001 1.48
Implementation on January 1, 2002
4.12 Wide range pH test paper;
4. 13 Silicone grease.
5 Instruments
General laboratory instruments, as well as:
GB/T 8572 - 2001
5.1 Digestion instrument: 1000mL round-bottom distillation flask (matching the distillation instrument) and pear-shaped glass funnel; 5.2 Steaming stuffing instrument: equipped according to GB/T2441.1; 5.3 Anti-violent particles or anti-violent device: the latter consists of a glass rod about 100mm long and 5mm in diameter connected to a polyethylene tube about 25mm long;
5.4 Digestion heating device: a 1500W electric furnace placed in a fume hood, or other forms of heat sources that can make 250mL of water boil violently from room temperature within 7min8min;
5.5 Distillation heating device: 1000W~1500W electric furnace, placed on a lifting platform, the height of which can be freely adjusted. A temperature-controlled electric furnace or other forms of heat sources that can adjust the heating intensity can also be used. 6 Analysis steps
6.1 Sample
Prepare the sample according to GB/T8571.
If the sample is difficult to crush, grind it until it passes through a 2mm test sieve. Weigh 0.5g to 2g (accurate to 0.0002g) of the sample with a total nitrogen content of no more than 235mg and a nitrate nitrogen content of no more than 60mg into a distillation flask.
6.2 Sample treatment and distillation
6.2.1 Sample containing only ammonium nitrogen
6.2.1.1 Add 300mL of water to the distillation flask, shake it to dissolve the sample, put in the anti-boiling material, and connect the distillation flask to the distillation device.
2 Add 40.0mL sulfuric acid solution Lc (1/2H2SO4) = 0.5mol/L.] or 20.0mL sulfuric acid solution 6.2.1.2
[c (1/2H2SO4) = 1mol/L], 4~5 drops of mixed indicator, and add appropriate amount of water to ensure the closed gas outlet, and connect the receiver to the distillation device.
The ground joints of the distillation device should be sealed with silicone grease. Add 20mL sodium hydroxide solution (4.8) through the dropping funnel of the distillation device. When the solution is about to flow out, add 20~30mL water to rinse the funnel. When 3~5mL of water is left, close the piston. Turn on the cooling water and the heating device (5.5) at the same time. When boiling, adjust the heating intensity according to the degree of foam generation to avoid foam overflow or droplets. After distilling at least 150mL of distillate, check the droplets at the outlet of the condenser with pH test paper. If there is no alkalinity, end the distillation.
6.2.2 For samples containing nitrate nitrogen and ammonium nitrogen, add 300 ml of water to the distillation flask, shake to dissolve the sample, add 3 g of nitrogen alloy and anti-boiling material, and connect the distillation flask to the distillation device.
During the distillation process, except for adding 20 ml of sodium hydroxide solution (4.8), let it stand for 10 min and then heat it up, the rest of the steps are the same as 6.2.1.2. 6.2.3 For samples containing amide nitrogen, cyanamide nitrogen and ammonium nitrogen, place the distillation flask in a fume hood, carefully add 25 ml of sulfuric acid (4.1), insert a pear-shaped glass funnel, and place it on the heating device (5.4); heat until white sulfuric acid smoke appears for 15 minutes, then stop, and carefully add 250 ml of water after the distillation flask cools to room temperature. The distillation process is the same as 6.2.1.2 except that 100 ml of sodium hydroxide solution (4.8) is added. 6.2.4 Samples containing organic matter, amide nitrogen, cyanamide nitrogen and ammonium nitrogen Place the distillation flask in a fume hood, add 22 g of mixed catalyst, carefully add 30 ml of sulfuric acid (4.1), insert a pear-shaped glass funnel, and place it on a heating device (5.4) Heat.
GB/T 8572—2001
If there is a lot of foam, reduce the heating intensity until the foam disappears, continue heating until white sulfuric acid smoke appears for 60 minutes or until the solution becomes transparent. After the flask cools to room temperature, carefully add 250mL of water. The distillation process is the same as 6.2.1.2 except that 120mL of sodium hydroxide solution (4.8) is added. 6.2.5 For samples containing nitrate nitrogen, amide nitrogen, cyanamide nitrogen and ammonium nitrogen, add 35mL of water to the distillation flask, shake to dissolve the sample, add 1.2g of chromium powder and ?ml of hydrochloric acid, let it stand for 5~10min, and insert a pear-shaped glass funnel. www.bzxz.net
Place the distillation flask on the heating device (5.4) in the fume hood, heat until boiling and foaming for 1 minute, cool to room temperature, carefully add 25ml of sulfuric acid (4.1), continue heating until white sulfuric acid smoke appears for 15 minutes, and carefully add 400ml of water after the distillation flask cools to room temperature. The distillation process is the same as 6.2.1.2 except that 100ml of sodium hydroxide solution (4.8) is added. 6.2.6 For samples containing organic matter, nitrate nitrogen, amide nitrogen, cyanamide nitrogen and ammonium nitrogen or unknown samples, add 35ml of water to the distillation flask, shake to dissolve the sample, add 1.2g of chromium powder and 7ml of hydrochloric acid, let it stand for 5~10min, and insert a pear-shaped glass funnel.
Place the distillation flask on the heating device (5.4) in the fume hood, heat until boiling and foaming for 1 minute, cool to room temperature, add 22g of mixed catalyst, carefully add 30ml sulfuric acid (4.1), and continue heating. If there is a lot of foam, reduce the heating intensity until the foam disappears, continue heating until white smoke of bone sulfuric acid appears for 60 minutes, then stop, and carefully add 400ml of water after the distillation flask cools to room temperature.
Except for adding 120mL of sodium hydroxide solution (4.8) during the distillation process, the remaining steps are the same as 6.2.1.2. 6.3 Titration
Back-titrate the excess sulfuric acid with sodium hydroxide standard titration solution (4.9) until the mixed indicator turns gray-green as the end point. 6.4 Blank test
At the same time as the determination, perform a blank test according to the same operating steps, using the same reagents but without the sample. 6.5 Verification test
Use freshly prepared ammonium nitrate containing 100 mg of nitrogen and carry out the test under the same conditions as the test sample. 7 Expression of analytical results
7.1 Calculation of analytical results
The total nitrogen content (X) is expressed as the mass fraction (%) of nitrogen (N) and is calculated as follows: X = V,-Vvc× 0. 014 01 × 100m
Where: --Concentration of sodium hydroxide standard titration solution used in determination and blank test, mol /I., V,-Volume of sodium hydroxide standard titration solution used in determination, mL; V2-Volume of sodium hydroxide standard titration solution used in blank test, mL; 0.01401The mass of nitrogen expressed in grams equivalent to 1.00mL sodium hydroxide standard titration solution Lc(NaOH)=1.000mol/L;
Sample mass g.
Take the arithmetic mean of the parallel determination results as the determination result. 7.2 Allowable Difference
The absolute difference of the parallel determination results shall not exceed 0.30%; the absolute difference of the determination results of different laboratories shall not exceed 0.50%. 130
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