How to determine the Nitrogen Content of compound fertilizer using lab formula?

Compound fertilizer nitrogen content inspection basis and standards applied:
- GB15063-2009 Compound fertilizer (compound fertilizer).
- GB21633-2008 Blended fertilizer.
- GB/T8572-2010 Determination of total nitrogen content in compound fertilizers – Titration method after distillation.
- GB/T8573-2010 Determination of available phosphorus content in compound fertilizers.
- GB/T8574-2010 Determination of potassium content in compound fertilizers – Potassium tetraphenylborate gravimetric method.
- GB/T8576-2010 Determination of free water content in compound fertilizers – Vacuum oven method.
- GB/T8570-2008 Numerical rounding rules and expression and determination method of limit values.
Compound fertilizer nitrogen content test sample reduction
- Quickly mix the collected samples, use a divider or the quartering method to divide the sample to about 1kg, then divide it into two parts, and pack them into two clean, dry 500ml plastic bottles, seal and label them. Use one bottle for product quality analysis and keep the other bottle for two months for future reference.
Compound fertilizer nitrogen content sample preparation
- Take out about 100g of the sample from one bottle in 2.1 after multiple reductions, grind it quickly until all the samples pass through a 0.5mm aperture sieve, mix well, and place it in a clean, dry bottle for composition analysis. The remaining sample was used for particle size determination.
5 steps for measuring sample total nitrogen content:
Step 1: Fertilizer sample weighing
According to the nitrogen content label, weigh about 0.5~1.0g of the sample (total nitrogen is not more than 235mg) in the distillation flask, accurate to 0.0001g.
Step 2: Fertilizer sample pre-treatment
According to the raw materials of the sample, and in accordance with the provisions of 6.2 in GB/T8572-2010, the sample mainly contains amide nitrogen and ammonium nitrogen, and 25 ml of sulfuric acid is added for digestion.
Step 3: Fertilizer sample distillation
- After cooling the processed sample to room temperature, add about 300ml of water to the distillation flask, put in anti-bump material and connect the distillation flask to the distillation device.
- Add 40.0ml of sulfuric acid solution [c (1/2H2SO4) = 0.5mol/L] into the receiver, 4 or 5 drops of mixed indicator, and add an appropriate amount of water to ensure that the gas outlet is sealed, and connect the receiver to the distillation on the device.
- Apply silicone grease to the ground joint of the distillation unit to seal it.
- Add 120 ml of sodium hydroxide solution through the dropping funnel of the distillation device. When the solution is about to run out, add 20 to 30 ml of water to rinse the funnel. Close the piston when 3 to 5 ml of water remain. Turn on the cooling water and the heating device at the same time.
- After distilling at least 150ml of distillate, use a pH test paper to check the droplets at the outlet of the condenser tube. If there is no alkalinity, end the distillation.
Step 4: fertilizer solution sample titration
Back-titrate excess sulfuric acid with sodium hydroxide standard titration solution until the mixed indicator turns gray-green as the end point.
Step 5: fertilizer solution sample blank test
At the same time as the measurement, follow the same operating steps and use the same reagents, but without the sample, perform a blank test.
Fertilizer nitrogen content calculation formula step by step
The total nitrogen content X1 is expressed as the mass percentage of nitrogen and is calculated according to the following formula:
- X1=(V2-V1)*C*0.01402*100/m
In the formula:
- V2——The volume of sodium hydroxide standard titration solution used in blank test, unit is milliliter, ml
- V1——When measuring, use the volume of sodium hydroxide standard titration solution, the unit is milliliter, ml
- C——Concentration of sodium hydroxide standard titration solution, mol/l
- m——sample mass, g
- 0.01402——Numerical value of millimole mass of nitrogen, g/mmol
Take the arithmetic mean of parallel measurement results as the measurement result.
Fertilizer nitrogen content calculation formula standard deviation
The absolute difference aka the standard deviation of parallel measurement results is not greater than 0.30%
Precautions during the determination of vanadium content in fertilizers
- The compound fertilizer must be completely melted. Whether it is completely melted or not mainly depends on the melting temperature. If the temperature is too low, the melting will be incomplete; but if the temperature is too high, it will lead to the loss of nitrogen.
- Generally, the heat source requirement is to achieve a boiling test of 7 to 7.5 minutes. The so-called boiling test is to add 250ml of distilled water to a distilling bottle and heat it on an electric stove. If the water at 25°C reaches a violent boil within 7 to 7.5 minutes, the heating of the electric stove meets the melting requirements.
- Before distillation, you should check whether each connecting joint is sealed. The ground joint should be coated with silicone grease and fixed with a rubber band to prevent the joint from loosening during distillation, causing gas or liquid to leak out and lower the result.
- An appropriate amount of water should be added to the receiver to ensure that the gas outlet is sealed.
- Excess sodium hydroxide should be added during distillation. If the amount added is not enough, the ammonium ions cannot be completely converted into ammonium hydroxide.
- Distillation should be complete. To ensure complete distillation, the distillate should generally reach about 150ml. If the room temperature is too high during distillation, it will also lead to incomplete distillation. Generally, the room temperature is below 35°C.
Conclusion: How to calculate Nitrogen content of fertilizer
To summarize, in this article we introduced how to measure the nitrogen content in compound fertilizers. The method used is to take some samples of compound fertilizers and then dilute them, record the data through distillation, and finally bring it into the calculation formula of the nitrogen content of compound fertilizers. Perform calculations and finally draw conclusions. This is an internal document of the compound fertilizer factory laboratory, used to train new employees in the laboratory