Haineng Instrument: Determination method of soil cation exchange amount (cation exchange amount measuring instrument)-华强电子网

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In accordance with "LYT 1243-1999 Determination of cation exchange capacity in forest soils." The soil sample is treated repeatedly with a 1 mol/L ammonium acetate solution to saturate the soil with ammonium ions. Excess ammonium acetate is then removed using 95% ethanol, followed by the addition of magnesium oxide and distillation. The distilled ammonia is absorbed by a boric acid solution and titrated with a standard acid solution. The cation exchange capacity (CEC) is calculated based on the amount of ammonium ions retained.

K1160 automatic Kjeldahl analyzer (cation exchange meter)

Analytical balance (one in ten thousand)

Centrifuge (100ml centrifuge tube)

Reagent configuration reference: LYT 1243-1999 Determination of cation exchange capacity in forest soils.

1) Ion Exchange

Weigh 2g of air-dried soil through a 1mm sieve and place it into a 100ml centrifuge tube. Add a small amount of 1mol/L ammonium acetate solution along the wall and stir the soil with a rubber-headed glass rod to create a uniform slurry. Then add ammonium acetate solution to reach a total volume of 60ml, mix thoroughly, and rinse the rod with more solution before transferring it to the centrifuge tube.

The centrifuge tube is balanced with ammonium acetate solution and placed symmetrically in the centrifuge at 3000r/min for 3-5 minutes. The supernatant is collected in a 250ml volumetric flask and washed 2-3 times with ammonium acetate until no calcium ions are detected in the leachate.

To check for calcium ions: Take 5ml of leachate, add 1ml of pH 10 buffer solution, and a few drops of KB indicator. If the solution turns blue, there are no calcium ions; if it turns purple, calcium ions are present. Finally, adjust the volume with ammonium acetate and retain the supernatant for further analysis.

2) Repeated Washing

Add a small amount of 95% ethanol to the centrifuge tube and stir the soil with a rubber-headed glass rod to make it a mud-like consistency. Then add ethanol to about 60ml, mix well, and wash away excess ammonium acetate. Ensure no clumps remain.

Centrifuge the tube at 3000r/min for 3-5 minutes and discard the ethanol solution. Repeat this process 2-3 times with fresh ethanol until the final solution contains no ammonium ions. To check for ammonium ions, add a drop of Nessler's reagent to the ethanol solution. If no yellow color appears, it indicates no ammonium ions are present.

3) On-Machine Test

Rinse the outer wall of the centrifuge tube with water and add a small amount of water to create a paste. Wash the slurry into the digestion tube with water, and clean the inner walls of the tube with a rubber-headed glass rod. Transfer all soil samples to the digestion tube, ensuring the total volume of washing water is between 50-80ml.

Add 2ml of liquid paraffin and 1g of magnesium oxide to the digestion tube. Immediately place the tube into the instrument according to the setup instructions as shown in the image below.

Each soil sample should be tested in parallel at least twice, and a blank test must also be conducted.

4) Instrument Output

The instrument automatically performs titration and provides the cation exchange capacity. The built-in calculation formula used by the instrument is as follows:

Where:

CEC: Cation exchange capacity, cmol(+)/kg;

C: Concentration of hydrochloric acid standard solution, mol/L;

V: Volume of hydrochloric acid standard solution, mL;

Vâ‚€: Volume of blank test hydrochloric acid standard solution, mL;

m₁: Mass of air-dried soil sample, g;

Kâ‚‚: Conversion factor from air-dried soil to dry soil;

10: Conversion factor from mmol to cmol.