How to test the chlorine content and particle size of NPK compound fertilizer

What is chlorine’s function in fertilizer?

Chlorine in compound fertilizer is one of the indispensable elements for crops. It is a trace element with important physiological functions and plays an important role in plant growth and development. The main function of chlorine in crops is to participate in photosynthesis and respiration, promote metabolism and energy conversion of plant cells, and also protect crops from pests and pathogenic bacteria. But how do you know if the fertilizer you purchased is qualified in terms of chlorine content? In this article we are going to show you step by step.

How to test the chlorine content in npk fertilizer?

Step 1: Test the particle size of the fertilizer

First step is to measure the particle size and prepare for mkaing the solution, the equipment that is need to perform the above testing is a test sieve:

1.00mm, 4.75mm with chassis and sieve cover. (Blended fertilizer test sieve specifications 2.00mm, 4.00mm)

Step 2: Measure the particle size of the fertilizer.

According to the size of the product particles, stack the sieves in order of 1.00mm and 4.75mm and install them on the chassis. Weigh about 200g of the reduced laboratory sample (accurate to 0.5g) and place it on the stacked sieves. Cover the sieve cover. Sift for 5 minutes. Weigh the sample between 1.00mm and 4.75mm (accurate to 0.5g). The sample caught in the sieve holes will not pass through this sieve.

Step 3: Calculate the particle size of the chlorine fertilizer

Particle size w1 is calculated based on the mass fraction of the sample with a particle size of 1.00 mm to 4.75 mm in all samples. The value is expressed in % and is calculated according to the following formula:

W1=m1/m*100

Step 4: Prepare the chlorine fertilizer solution.

Weigh about 5g of the sample (accurate to 0.0001g), add 100ml of water to a 250ml beaker, slowly heat to boiling, continue to boil slightly for 10 minutes, and cool to room temperature.
Transfer the solution to a 250ml measuring flask, dilute to volume and mix well, dry filter and discard the first 50ml of filtrate.
Accurately draw 25.0ml of the filtrate into a 250ml Erlenmeyer flask, add 5ml of nitric acid solution, add 25.0ml of silver nitrate solution, shake until the precipitation separates, add 5ml of dibutyl phthalate, and shake for a while.
Add water to make the total volume of the solution about 100 ml, add 2 ml of ferric ammonium sulfate indicator solution, and titrate the remaining silver nitrate with ammonium thiocyanate standard solution until light orange-red or light brick green appears, and perform a blank test at the same time.

Step 5: Calculation of chlorine content using formla equation.

The mass fraction (%) of chloride ion X6 is calculated according to the following formula:

X6=(V0-V2)*c*35.46/m3

In the formula:

V0——The volume of ammonium thiocyanate standard titration solution consumed in the blank test, in milliliters (ml)
V2——The volume of ammonium thiocyanate standard titration solution consumed in the titration test, in milliliters (ml)
c——Concentration of ammonium thiocyanate standard titration solution, unit mole per liter (mol/l)
0.03546——The value of millimole mass of chlorine, unit is (g/mmol)
m3——The mass of the sample, unit is g

Take the arithmetic mean of the parallel measurement results as the measurement result.
The absolute difference of parallel measurement results should be ≤0.40%.

Step 6: 3 things to note when performing the test.

The control of the titration endpoint and the depth of the endpoint color will directly affect the accuracy of the test results. The test method for chloride ion content is the back titration method in volumetric analysis. The end point is a light orange-red or light brick red color, which is difficult to control. In particular, some samples themselves are colored, which leads to incorrect judgment of the end point and inaccurate test data.
The concentration of ammonium thiocyanate standard titration solution should be accurate. The calibrated ammonium thiocyanate standard titration solution is prepared from a standard sodium chloride solution that has been dried at 270°C to 300°C to a constant weight. Therefore, the purity of the sodium chloride and the degree of drying will affect the ammonium thiocyanate. The concentration of the standard titration solution is accurate or not.
Blank test. When testing chloride ions, it is required that the titration endpoint of the blank test must be consistent in color with the titration endpoint of the sample, otherwise deviation will occur.

3 Adventages of compound fertilizer containning chlorine

1. Nutrient balance of chlorine-containing compound fertilizer

Chlorine-containing compound fertilizer has three main nutrients: nitrogen, phosphorus and potassium, as well as a small amount of medium and trace elements, such as calcium, magnesium, sulfur, etc. These nutrients play an important role in plant growth, promoting plant growth and development, and improving crop stress resistance and yield.

2. The fertilizer effect of chlorine-containing compound fertilizer is long-lasting.

The chlorine element in chlorine-containing compound fertilizer can promote the transformation and release of nutrients in the soil, making the fertilizer effect more lasting. At the same time, chlorine-containing compound fertilizer also has better water solubility and diffusibility, and can be better absorbed and utilized by crops. This kind of fertilizer can reduce the frequency of fertilization to a certain extent, reduce labor intensity, and improve agricultural production efficiency.

3. The improvement effect of chlorine-containing compound fertilizer on soil

Chlorine-containing compound fertilizers have a certain improvement effect on soil. An appropriate amount of chlorine can promote the formation of aggregate structures in the soil, improve the soil’s ability to retain water and fertilizer, and enhance soil permeability and root activity. In addition, chlorine-containing compound fertilizers can also inhibit harmful microorganisms in the soil and reduce the occurrence of pests and diseases, thus helping to maintain soil health and sustainable utilization.

Conclusion:

In this article, we introduce what chlorine in compound fertilizers is and the effect of chlorine on plants. So how to identify whether the chlorine content of compound fertilizers meets the standard? We introduced it in detail in the article, showing how to test the particle size of the particles, then make the compound fertilizer into a solution and conduct component testing, and finally use a formula to calculate the chloride ion content. Finally, we introduced the advantages of chlorine-containing compound fertilizers.