How to calculate fertilizer phosphrous composition using lab formula method?

How to calculate fertilizer phosphrous composition using lab formual method?

General introduction: How to calculate phosphrous content of compound fertilizer.

In daily life, when you buy a package of fertilizer, do you want to see if the ingredients in the fertilizer are consistent with what is labeled on the package? Of course, the fertilizer ingredients of most manufacturers are up to standard, so just in case if you want to measure the ingredient content of fertilizer yourself or you are a college student writing a thesis on fertilizer ingredients, this article will teach you step by step. Fertilizer phosphrous content determination method

Npk compound fertilizer phosphrous sample weighing

Weigh about 1g of the sample (containing 100 to 200 mg of phosphorus pentoxide), accurate to 0.0001g.

Extraction of fertilizer water-soluble phosphorus:

Place the sample in a 75ml mortar, add 25ml of water and grind it. Pour and filter the clear liquid into a 250ml measuring bottle with 5ml of nitric acid solution added in advance. Continue grinding with water for 3 times, each time with 25ml of water. Then remove the water-insoluble matter. Transfer to filter paper and wash the water-insoluble matter with water until the solution in the measuring bottle reaches 200ml. Finally dilute to volume with water. Mix well to obtain solution A, which is used for measuring water-soluble phosphorus.

Extraction of available phosphorus from fertilizer solution:

According to the weighing requirements, weigh the sample and place it on the filter paper, wrap the sample with filter paper, put it into a 250ml measuring bottle, add 150ml EDTA solution, plug the bottle stopper tightly, shake the measuring bottle to disperse the sample in the solution, and place it Keep warm and shake for 1 hour in a constant temperature water bath oscillator at 60±1°C. Then take out the measuring flask, cool to room temperature, dilute to the mark with water, mix well, dry filter, discard the first 50ml of filtrate, and obtain solution B for measuring available phosphorus.

Determination of water-soluble phosphorus:

Use a single-line pipette to absorb 25 ml of solution A, transfer it to a 500 ml beaker, add 10 ml of nitric acid (1+1) solution, dilute to 100 ml with water, heat to boiling on an electric stove, remove, add 35 ml of quinolinone reagent, and cover Put the watch glass on the electric hot plate and boil it slightly for 1 minute, remove it and cool it to room temperature.
Use a No. 4 glass crucible filter that has been dried to constant weight in a drying oven at 180±2°C to filter. First filter the supernatant, and then wash the precipitate 1 to 2 times with the pouring method, using 25 ml of water each time.
Transfer the precipitate to the filter and wash with water. The total water used is about 100~125ml. Place the crucible containing the precipitate in a drying box at 180±2°C. After the temperature reaches 180°C, dry it for 45 minutes, take it out and move it into a desiccator, cool and weigh.

Determination of available phosphorus in compound fertilizer:

Use a single-line pipette to absorb 25 ml of solution B, transfer it to a 500 ml beaker, add 10 ml of nitric acid (1+1) solution, dilute to 100 ml with water, heat to boiling on an electric stove, remove, add 35 ml of quinolinone reagent, and cover Put the watch glass on the electric hot plate and boil it slightly for 1 minute, remove it and cool it to room temperature.
Use a No. 4 glass crucible that has been dried to constant weight in a drying oven at 180±2°C to filter. First filter the supernatant, and then wash the precipitate 1 to 2 times with the pouring method. Use 25 ml of water each time to remove the precipitate. Transfer to a filter and wash with water. The total water used is about 100~125ml.
Place the crucible containing the precipitate in a drying box at 180±2°C. After the temperature reaches 180°C, dry it for 45 minutes, take it out and move it into a desiccator, cool and weigh.

Fertilizer phosphrous content calculation formula step by step guide:

Water-soluble phosphorus content X2 and available phosphorus content

X2=(m1-m2)*32.07/ma
X3=(m3-m4)*32.07/mb

In the formula:

m1——The mass of quinoline phosphomolybdate precipitate obtained by measuring water-soluble phosphorus, unit is grams (g).
m2——When measuring water-soluble phosphorus, the mass of quinoline phosphomolybdate precipitate obtained from the blank test, the unit is grams (g).
m3——The mass of quinoline phosphomolybdate precipitate obtained from the determination of available phosphorus, unit is grams (g).
m4——When measuring available phosphorus, the mass of quinoline phosphomolybdate precipitate obtained from the blank test, the unit is grams (g).
mA——When measuring water-soluble phosphorus, the mass of the sample, the unit is grams (g).
mB——The mass of the sample when measuring available phosphorus, in grams (g).
0.03207——The coefficient for converting the mass of quinoline phosphomolybdate into the mass of phosphorus pentoxide.

Take the arithmetic mean of the parallel measurement results as the measurement result.

Allowable difference/standard deviation: The absolute difference of parallel measurement results is not greater than 0.20%.

7 things to notice during the operation of calculate fertilizer phosphrous composition while using the formula.

When extracting water-soluble phosphorus, the sample should be carefully ground three times. When washing the water-insoluble matter on the filter paper with water, wait until the solution in the measuring bottle reaches about 200ml.
When extracting available phosphorus, the concentration of EDTA solution should be prepared according to standard regulations, and the EDTA solution is 37.5g/l.
When extracting available phosphorus, the extraction temperature, oscillation frequency and extraction time should be strictly controlled. The extraction temperature is strictly controlled at 60±1°C, the shaking frequency is sufficient to allow the sample in the measuring bottle to flip freely, and the extraction time is 1 hour.
During the operation of measuring phosphorus, adding 35 ml of quinolinone reagent can only precipitate 25 mg of phosphorus pentoxide. Therefore, when absorbing the extract, it is appropriate to use no more than 20 mg of phosphorus pentoxide.
The solution temperature when adding quinolone reagent is preferably around 80°C. After adding the reagent, the temperature drops to around 60°C. If the temperature is too low, it is easy to form a precipitate with poor physical properties.
Quinolinone reagent can corrode glass, so it should be kept in a dark place in a polyethylene bottle.
The No. 4 glass crucible filter used to filter the yellow precipitate should be washed away with water after use, and then soaked in 1+1 ammonia water. After the yellow precipitate is completely dissolved, it should be washed with clean water.

Conclusion: how to calculate phosphrous content in fertilizer.

This article introduces how to make compound fertilizer into a solution and use the compound fertilizer solution to measure the phosphorus content. I hope it can help people in need. In our next article, we will introduce how to use the compound fertilizer potassium chloride. The ingredients are measured.