Determination of Total Nitrogen in Nitrogen Fertilizers

Determination of Ammonium Nitrogen in Nitrogen Fertilizer
The nitrogen fertilizer containing ammonium nitrogen is generally soluble in water, can be distilled in an alkaline medium to escape ammonia, and then absorbed by boric acid, titrated with standard hydrochloric acid, and the amount of nitrogen contained is calculated according to the amount of acid consumed.
Operation steps: Weigh 0.5-1.0g (accurate to 0.0001g) of nitrogen fertilizer sample in 100ml beaker, dissolve it with 20~30ml distilled water, transfer and dilute to 100ml, shake up and take 25ml in Kjeldahl bottle. Alkali distillation, titration and calculation.
Determination of nitrate ammonia in nitrogen fertilizers (Zn-FeSO4 alkaline medium reduction distillation nitrogen determination method)
Principle of the method: In a strong alkaline solution, zinc reacts with sodium hydroxide to form hydrogen, and reduces nitrate nitrogen to nitrite nitrogen. At the same time, it also reduces high-priced iron to low-priced iron, so that the ferrous iron exists repeatedly. The ferrous iron reduces nitrate nitrogen and nitrite nitrogen to ammonia. The ammonia distilled at the same time of reduction is absorbed by boric acid, titrated with standard hydrochloric acid, and the content of nitrate nitrogen is calculated. The main reaction is as follows:  FeSO4+2NaOH → Fe(OH) 2↓+Na2SO4
8Fe (OH) 2 + NaNO3 + 6H2O → 8Fe (OH) 3 + NaOH + NH3 
Zn+2NaOH → Na2ZnO2+H2
H2+NaNO3 → NaNO2+H2O
6Fe(OH)2+NaNO2+5H2O → 6Fe(OH)3+NaOH+NH3 
The nitrogen determined by the method is substantially the total amount of ammonium nitrogen and nitrate nitrogen. If it is necessary to separately determine the content of ammonium nitrogen and nitrate nitrogen, and only add sodium hydroxide solution for distillation, absorption and titration, it is ammonium. Nitrogen; then adding zinc-ferrous sulfate reducing agent to the Kjeldahl bottle for distillation, absorption, and titration, which is nitrate nitrogen.
Instruments: nitrogen distillation unit, burette, Kjeldahl bottle, etc. Reagents : (1) Zinc powder-ferrous ferrous sulfate reducing agent: Weigh 50 g of chemically pure ferrous sulfate and 10 g of zinc powder in a porcelain mortar, and then pass through a 60-mesh sieve, mix and store in a brown grinding machine. Spare in the bottle.
(2) 40% sodium hydroxide solution: 400 g of chemically pure sodium hydroxide is dissolved in water, diluted to 1 liter, and stored in a plastic bottle for use.
(3) 2% boric acid solution:
(4) Fixed nitrogen mixed indicator:
(5) 0.02mol/L standard hydrochloric acid solution:
(6) liquid paraffin
Operation steps: Weigh 1.1xxg of fertilizer sample into a 50ml beaker, add a small amount of water to dissolve and transfer it to a 100ml volumetric flask without damage. Shake well after constant volume. Pipette 10-20 ml of this solution (so that the nitrogen content is about 20-30 mg) in a 250 ml Kjeldahl bottle, add 1.5-3.0 g of Zn-FeSO4 reducing agent, and immediately add 40 ml of NaOH 10 ml to heat, distill, absorb and titrate.
Result calculation:
N%=(V-V0) × C×0.014/W×100
Where V: the volume of the test solution consumed by standard hydrochloric acid, ml;
V0 : blank consumption standard hydrochloric acid volume, ml;
C : concentration of standard hydrochloric acid, mol/L;
0.014 : millimolar mass of nitrogen atom, g/mmol;
W : absorbs the mass of 10 to 20 ml of the sample to be tested, g.
Determination of nitrogen in urea
Principle of the method: Urea is a nitrogen fertilizer containing amide nitrogen. It can not be directly distilled by adding alkali. The aqueous solution can be hydrolyzed to ammonium nitrogen in the presence of sulfuric acid, and CO2 is evolved. The reaction formula of acid hydrolysis is
CO(NH2)2+2H2SO4+H2O → 2NH4HSO4+CO2↑
After zui, alkali distillation was carried out to determine the nitrogen content.
Instruments and reagents: determination of total nitrogen in soil
Operation steps: Weigh 0.2xxxg of urea sample dried at 75 °C, dissolve it with distilled water, dilute to 100ml, shake and set aside. Aspirate 5.00 ml of the test solution in a 150 ml Kjeldahl bottle, add 5 ml of concentrated sulfuric acid, first heat with a simmer until the CO2 is completely removed, and then increase the temperature to make the sulfuric acid smoke. Take off a little cooling, dilute to 70 ~ 80ml with water, and then distill and titrate according to the operation procedure of soil total nitrogen, calculate the result.