CN111812084A - A kind of inspection and detection method of organic matter content in soil - Google Patents

Abstract

The invention belongs to the field of organic matter detection, and discloses a method for detecting the content of organic matters in soil. The detection method comprises the following steps: (1) weighing a sample to be detected, putting the sample into a 250ml hard triangular flask, adding a potassium dichromate-sulfuric acid solution, shaking uniformly, and inserting a glass funnel into each triangular flask; (2) putting all the triangular bottles in iron reagent trays, putting the trays with the samples in an oven, keeping the temperature of 120 ℃ for baking for 2 hours, taking the trays out of the oven, cooling, directly washing the small funnel with water, and washing the washing liquid in the triangular bottles to control the total volume of the solution in the triangular bottles to be 50-60 mL; (3) adding 3 drops of phenanthroline indicator, titrating residual K with ferrous sulfate standard solution₂Cr₂O₇The color change process of the solution is orange-blue-green-brownish red. The method does not require in-vitroThe digestion solution is washed out, the defects of the prior art do not exist, the organic matters in the soil can be detected in large batch, and the method is simple to operate, environment-friendly, efficient, safe and reliable.

Description

A kind of inspection and detection method of organic matter content in soil

technical field

The invention relates to the field of organic matter detection, in particular to an inspection and detection method for the content of organic matter in soil.

Background technique

Soil organic matter content is an important indicator to measure soil fertility, and soil organic carbon fixation and changes are related to changes in atmospheric carbon dioxide concentration. Therefore, the rapid and accurate determination of soil organic matter content is the key to obtain soil fertility changes and soil organic carbon fixation, and is of great significance in soil fertility evaluation and mitigation of atmospheric carbon dioxide concentration.

There are many methods for soil organic matter detection, the common ones are oil bath and sand bath method, the most used is high temperature external thermal potassium dichromate oxidation-volume method, such as the method provided by the industry standard NY/T1121.6-2006: accurate weighing Air-dry 0.05g～0.5g of the sample through a 0.25mm aperture sieve (accurate to 0.0001g, and the weighing sample amount is determined according to the range of organic matter content), put it into a rigid test tube, and then accurately add 10.00mL0.4mol/ L potassium dichromate-sulfuric acid solution, shake well and insert a glass funnel into the mouth of each test tube; insert the test tubes into the wire cage one by one, and then sink the wire cage into the oil bath that has been heated to 185℃～190℃ on the electric furnace In the pot, make the liquid level in the tube lower than the oil level. It is required that the temperature of the oil bath drop to 170℃～180℃ after putting it in. When the solution in the test tube boils, start timing. At this moment, the temperature of the electric furnace must be controlled to prevent the solution from boiling violently. During the process, the wire cage can be gently lifted and shaken several times in the oil bath to make the liquid temperature uniform and maintained at 170℃～180℃. After 4.5min～5.5min, lift the wire cage out of the oil bath and let it cool for a while , wipe off the oil (wax) liquid outside the test tube; transfer the cooking liquid and soil residues in the test tube into a 250mL triangular flask without damage, rinse the test tube and small funnel with water, and merge the washing liquid into the triangular flask, so that the inner The total volume of the solution is controlled at 50mL-60mL; 3 drops of phenanthroline indicator are added, and the remaining K ₂ Cr ₂ O ₇ is titrated with ferrous sulfate standard solution. The discoloration process of the solution is orange-yellow-blue-green-brown-red. In this method, if the number of milliliters of ferrous sulfate solution used in the titration is less than 1/3 of the number of milliliters of ferrous sulfate solution consumed in the blank test, the soil weighing sample should be reduced and remeasured. For a blank test, take about 0.2g of burning pumice powder or soil instead of soil sample, and other steps are the same as soil sample determination.

However, there are many defects in the above-mentioned method, such as (1) transfer the boiling liquid and soil residue in the test tube into a 250mL conical flask without damage, so there is one more link, and the steps are cumbersome, (2) the wire cage is removed from the bath pot. It is not environmentally friendly, and (3) the workload is large. Before each measurement, it is necessary to determine the amount of chloride ions in the soil. Based on chlorine Only the content of ions can determine the amount of silver sulfate to be added. The operation is also more troublesome, and batch testing is inconvenient. (4) The oil bath oxidation of soil organic matter is very troublesome to operate. First, the temperature of the electric furnace must be controlled to prevent the solution from boiling violently. , (paraffin) oil is easy to splash on the inspection personnel, there is a potential safety hazard, and the temperature of the electric furnace is difficult to control, (5) the maximum degree of oxidation of organic matter by potassium dichromate-concentrated sulfuric acid external heating method is only 95%, which cannot be achieved. The complete oxidation of organic matter will result in errors.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the above-mentioned background technology, and provide a method for testing the content of organic matter in soil. The method does not need to wash out the digestion liquid in the test tube, does not have the above-mentioned defects of the prior art, can detect the organic matter in the soil in large quantities, is simple to operate, environmentally friendly, efficient, safe and reliable.

In order to achieve the purpose of the present invention, the inspection and detection method of the organic matter content in the soil of the present invention includes the organic matter inspection of the air-dried soil sample and the organic matter inspection of the blank sample, wherein the organic matter inspection of the air-dried soil sample comprises the following steps:

(1) Accurately weigh 0.05-0.5g of the air-dried soil sample to be tested (accurate to 0.0001g, and the weighing sample size is determined according to the range of organic matter content), put it into a 250ml hard conical flask, and then accurately add it from an automatic zero-adjusting burette 10.00ml 0.4mol/L potassium dichromate-sulfuric acid solution, shake well and insert a glass funnel into each conical flask;

(2) Put all the triangular flasks in the iron reagent tray, heat the oven to a constant temperature of 120 °C in advance, put the tray with the sample into the oven and keep it at 120 °C for 2 hours, shake it once in the middle, and put the tray after 2 hours. Take it out of the oven, cool it for a while, rinse the small funnel directly with water, and wash the lotion into the triangular flask, so that the total volume of the solution in the triangular flask is controlled at 50mL to 60mL;

(3) Add 3 drops of phenanthroline indicator, titrate the remaining K ₂ Cr ₂ O ₇ with ferrous sulfate standard solution, and the discoloration process of the solution is orange-yellow-blue-green-brown-red;

During each batch of analysis, two blank tests are performed at the same time. The method for testing the organic matter of the blank sample is as follows: take 0.18-0.22g of burned soil or pumice powder instead of the air-dried soil sample to be tested as a blank sample, and the other steps are the same as Described steps (1)-(3) are identical;

Finally, the organic matter content in the soil to be tested was calculated from the organic matter test results of the air-dried soil samples and blank samples.

Further, in described step (2), if the milliliter of ferrous sulfate solution used in titration is less than one-third of the milliliter of ferrous sulfate solution used in blank test, then the air-dried soil test to be inspected in step (1) should be reduced. Sample size retest.

Further, the calculation result of the organic matter content in the soil to be tested is:

In the formula: O.M—the mass fraction of soil organic matter, in grams per kilogram (g/kg);

V ₀ —volume of ferrous sulfate standard solution consumed by blank test, mL;

V—the volume of ferrous sulfate standard solution consumed by the determination of the air-dried soil sample to be tested, mL;

C—the concentration of ferrous sulfate standard solution, mol L ^-1 ;

0.003—1/4 millimolar mass of carbon atoms, g;

1.724—the coefficient converted from organic carbon to organic matter;

1.10—Oxidation correction coefficient;

m—weigh the mass of the dried sample, g;

1000—converted to the content per kilogram;

The results of parallel determinations are expressed as the arithmetic mean, with three significant figures reserved.

Further, the organic matter content in the soil of the present invention is below 15%.

Compared with the prior art, the advantages of the present invention are as follows:

(1) The method of the present invention is compared with the NY/Y1121.6-2006 method, and the results are the same, but it is safer, simpler, environmentally friendly, fast, and has better re-dominance;

(2) The method of the present invention can detect the organic matter in the soil in large quantities, and can directly replace the test tube with a hard 150ml triangular flask, without washing out the digestion liquid in the test tube, so that a link is saved, and the large batch of The samples are placed directly in the iron tray, which is convenient, safe and fast.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention. It should be understood that the following description is only used to explain the present invention, but not to limit the present invention.

As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or device comprising the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article or device elements.

The main instruments and equipment of the present invention are as follows:

Oven, rigid triangular flask (150mL), small meniscus funnel, iron tray, auto-zero burette.

Unless otherwise specified, the reagents and water used in this test method refer to analytically pure reagents and tertiary water specified in GB/T6682. Said solution is an aqueous solution if no solvent is specified.

0.4mol/L potassium dichromate-sulfuric acid solution: Weigh 40.0g potassium dichromate (chemically pure) and dissolve it in 600ml~800ml water, filter it with filter paper into a 1L measuring cylinder, wash the filter paper with water, and add water to a 1L measuring cylinder, Wash the filter paper with water and add water to 1 L and transfer this solution into a large 3 L beaker. Take another 1L of concentrated sulfuric acid (chemically pure) with a density of 1.84g·cm- ³ , slowly pour it into the potassium dichromate aqueous solution, and keep stirring. In order to avoid rapid heating, stop for a while after adding about 100mL of concentrated sulfuric acid, and put the large beaker in a large plastic basin filled with cold water to cool it down. until all added, the concentration of this solution

0.1mol/L ferrous sulfate standard solution: Weigh 28.0g of ferrous sulfate (chemically pure) or 40.0g of ferrous ammonium sulfate (chemically pure) and dissolve it in 600mL~800mL of water, add 20mL of concentrated sulfuric acid (chemically pure) and stir well. After standing for a while, filter the filter paper into a 1L volumetric flask, then wash the filter paper with water and add water to the 1L volumetric flask, then wash the filter paper with water and add water to 1L (this solution is easy to be oxidized by air and the concentration will decrease. calibrate its exact concentration).

Calibration of 0.1mol/L ferrous sulfate solution: draw 20.00ml of 0.1000mol/L potassium dichromate standard solution and put it into a 150mL conical flask, add 3ml to 5ml of concentrated sulfuric acid and 3 drops of phenanthroline indicator, use bisulfite sulfate Iron solution titration, according to the consumption of ferrous sulfate solution, the consumption of ferrous sulfate solution can be calculated, and the accurate concentration of ferrous sulfate solution can be calculated.

Potassium dichromate standard solution: Accurately weigh 4.904g of potassium dichromate (superior pure) dried at 130°C for 2h to 3h, dissolve with a small amount of water, and then transfer it into a 1000mL volumetric flask without damage, add water to the volume, this standard Solution concentration

O-phenanthroline (C ₁₂ HgN ₂ .H ₂ O) indicator: Weigh 1.49g of o-phenanthroline and dissolve it in 0.70g FeSO ₄ .7H ₂ O or 1.00g (NH ₄ ) ₂ SO ₄ .FeSO ₄ . _6H2O in 100 mL of water.

The calculation results of the organic matter content in the soil to be tested are:

In the formula: O.M—the mass fraction of soil organic matter, in grams per kilogram (g/kg)

V ₀ —volume of ferrous sulfate standard solution consumed by blank test, mL;

V—the volume of ferrous sulfate standard solution consumed by the determination of the air-dried soil sample to be tested, mL;

C—the concentration of ferrous sulfate standard solution, mol L ^-1 ;

0.003—1/4 millimolar mass of carbon atoms, g;

1.724—the coefficient converted from organic carbon to organic matter;

1.10—Oxidation correction coefficient;

m—weigh the mass of the dried sample, g;

1000—converted to the content per kilogram;

The results of parallel determinations are expressed as the arithmetic mean, with three significant figures reserved.

The allowable difference values of parallel determination results are shown in the table below.

Organic matter content, g/kg Absolute difference allowed, g/kg <10 <0.5 10～40 <1.0

Example 1

Weigh 0.3368g, 0.3416g, 0.2705g (accurate to 0.0001) of 100 mesh air-dried soil samples into three glass conical flasks, add 10.00ml of 0.4mol/L potassium dichromate-sulfuric acid solution, shake well and place in Insert a glass funnel into each flask. Put all the triangular flasks in the iron reagent tray, heat the oven to a constant temperature of 120 °C in advance, put the tray with the sample in the oven and keep it at 120 °C for 2 hours, shake it once in the middle, and remove the tray from the oven after 2 hours. Take it out, cool it for a while, rinse the small funnel directly with water, wash the lotion into the triangular flask, control the total volume of the solution in the triangular flask to 50mL~60mL, add 3 drops of phenanthroline indicator, use ferrous sulfate standard solution Titrate the remaining K ₂ Cr ₂ O ₇ , and the discoloration process of the solution is orange-yellow-blue-green-brown-red.

Example 2

Using the method of NY/T 1121.6-2006, 0.3368g, 0.3416g, 0.2705g (accurate to 0.0001) of air-dried soil samples of 100 mesh were weighed into three rigid test tubes, and then 10.00ml of 0.4mol/L was added to the conical flask. Potassium dichromate-sulfuric acid solution, shake well and insert a glass funnel into the mouth of each test tube. Insert the test tubes into the wire cages one by one, and then sink the wire cages into the oil bath pot that has been heated to 185 ℃ ~ 190 ℃ on the electric furnace, so that the liquid level in the tubes is lower than the oil level, and the temperature of the oil bath is required to drop after being placed. When the temperature reaches 170℃-180℃, start timing when the solution in the test tube boils. At this moment, the temperature of the electric furnace must be controlled to prevent the solution from boiling violently. During this period, the wire cage can be gently lifted and shaken several times in the oil bath to make the liquid temperature uniform. , and maintained at 170 ℃ ~ 180 ℃, after 4.5min ~ 5.5min, lift the wire cage out of the oil bath, cool for a while, and wipe off the oil (wax) liquid outside the test tube. Transfer the digestion liquid and soil residue in the test tube into a 250mL conical flask without damage, rinse the test tube and small funnel with water, and add the washing liquid into the conical flask, so that the total volume of the solution in the conical flask is controlled at 50mL~60mL, add 3 drops of phenanthroline indicator, titrate the remaining K ₂ Cr ₂ O ₇ with ferrous sulfate standard solution, the discoloration process of the solution is orange-yellow-blue-green-brown-red.

Effect Example

The method of Example 1 of the present invention and the method of NY/Y1121.6-2006 of Example 2 are compared, and the results are the same, but they are safer, simpler, more environmentally friendly, and faster. The specific results are shown in the following table:

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (4)

1. The method for detecting the content of the organic matters in the soil is characterized by comprising an air-dried soil sample organic matter detection step and a blank sample organic matter detection step, wherein the air-dried soil sample organic matter detection step comprises the following steps:

(1) accurately weighing 0.05-0.5 g of an air-dried soil sample to be detected, putting the air-dried soil sample into a 250ml hard triangular flask, then accurately adding 10.00ml of 0.4mol/L potassium dichromate-sulfuric acid solution from an automatic zero setting burette, shaking uniformly, and inserting a glass funnel into each triangular flask;

(2) putting all triangular bottles in iron reagent trays, heating an oven to 120 ℃ in advance, keeping the temperature constant, putting the trays with samples in the oven, keeping the temperature at 120 ℃ for 2 hours, shaking once midway, taking the trays out of the oven after 2 hours, cooling for a moment, directly washing small funnels with water, washing the washing liquid in the triangular bottles, and controlling the total volume of the solution in the triangular bottles to be 50-60 mL;

(3) adding 3 drops of phenanthroline indicator, titrating residual K with ferrous sulfate standard solution₂Cr₂O₇The color change process of the solution is orange-blue-green-brownish red;

when each batch of analysis is carried out, 2 blank tests are simultaneously carried out, and the method for testing the organic matters in the blank samples comprises the following steps: taking 0.18-0.22g of burned soil or pumice powder to replace an air-dried soil sample to be detected as a blank sample, and the other steps are the same as the steps (1) - (3);

and finally, calculating the content of organic matters in the soil to be detected according to the organic matter detection results of the air-dried soil sample and the blank sample.

2. The method for detecting the content of organic matters in the soil according to claim 1, wherein in the step (2), if the milliliter number of the ferrous sulfate solution used for titration is less than one third of the milliliter number of the ferrous sulfate solution used for the blank test, the weight of the soil sample to be air-dried in the step (1) is reduced.

3. The method for detecting the content of organic matters in the soil according to claim 1, wherein the calculation result of the content of organic matters in the soil to be detected is as follows:

in the formula: O.M mass fraction of soil organic matter, unit is gram per kilogram;

V₀blank testTesting the volume of the consumed ferrous sulfate standard solution, namely mL;

v, determining the volume of the consumed ferrous sulfate standard solution mL of the air-dried soil sample to be detected;

c-concentration of ferrous sulfate Standard solution, mol L^-1；

0.003-1/4 carbon atoms, g;

1.724-coefficient converted from organic carbon to organic matter;

1.10-oxidation correction factor;

m-weighing the mass g of the dried sample;

1000-conversion to the content per kilogram;

the results of the replicates are represented by arithmetic means, with three significant figures being retained.

4. The method for detecting the content of organic matters in the soil according to claim 1, wherein the content of the organic matters in the soil is below 15%.