Soil total nitrogen determination

Soil total nitrogen determination

Soil total nitrogen determination techniques and methods,

Instruments: Temperature Control Furnace, Eliminating Tube, Nitrogen Distiller, Digestion Furnace

Reagents: 1. Sulfuric acid (GB 625-77): Chemically pure;

2. Sulfuric acid (GB 625-77) or hydrochloric acid (GB 622-77): analytically pure, 0.005 mol/L sulfuric acid or 0.01 mol/L hydrochloric acid standard solution;

3. Sodium hydroxide (GB 629-81): industrial or chemically pure, 10mol/L sodium hydroxide solution;

4. Boric acid-indicator mixture;

Boric acid (GB 628-78): analytically pure, 2% solution (W/V);

Mix indicator: 0.5g bromocresol green (HG3-1220-79) and 0.1g methyl red (HG3-958-76) in an agate mortar, add a small amount of 95% ethanol, grind until the indicator is completely dissolved, Add 95% ethanol to 100 ml. Prior to use, add 20 ml of mixed indicator per liter of boric acid solution and adjust to a reddish purple (pH about 4.5) with dilute base. The liquid should not be stored for too long. If there is a change in pH during use, it must be adjusted with dilute acid or dilute alkali at any time.

5. Accelerator: 100g of potassium sulfate (HG 3-920-76, chemically pure), 10g of copper sulfate pentahydrate (GB 665-78, chemically pure), 1g of selenium powder (HG3-926-76) in the mortar Must be fully mixed.

6. Potassium permanganate solution: 25g of potassium permanganate (GB 643-77) is dissolved in 500ml of ion-free water and stored in a brown bottle;

7. 1:1 sulfuric acid;

8. Reduced iron powder: ground through a 0.15mm (100 mesh) sieve;

Octanol.

Step by step, put the weighed soil sample on the decontamination tube, add reagents and drugs, and cook on the temperature-controlled electric furnace for the first time, 205 degrees for 45 minutes, then cool down, add reagents and drugs, and perform the second Cooking, 375 degrees for 4 hours. Next, the decontaminated soil liquid (detergent) is cooled and placed on a nitrogen determination instrument for distillation. The blue slip solution is then titrated with dilute sulfuric acid until it turns into a purple color, according to the titration used. The amount of soil total nitrogen was calculated from the amount of dilute sulfuric acid, the concentration, and the weight of the soil.

During the experiment, it is necessary to pay attention to putting the decontamination tube away, otherwise the decontamination fluid will be corroded by the determinator after the decontamination of the decontamination fluid through the high temperature. This will result in failure of the experiment. At the same time, a good decontamination tube should be selected and the material should be thicker.

Soil total nitrogen (%) = [(V-V0) × CH × 0.014/m] × 100

Where: V ─ volume of the acid standard solution used when titrating the test solution, ml;

V0── volume of the acid standard solution used when titrating the blank, ml;

CH── concentration of acid standard solution, mol/L;

0.014── The mass of nitrogen atoms;

M─ Dry soil quality, g.

6.2 Parallel determination results, expressed as an arithmetic average, with three decimal places retained.

6.3 The difference between the parallel determination results: When the soil nitrogen content is more than 0.1%, it shall not exceed 0.005%; when the nitrogen content is 0.1-0.06%, it shall not exceed 0.004%; if the nitrogen content is less than 0.06%, it shall not exceed 0.003%.