CN112014339A - Determination method for quickly extracting ammonia nitrogen in soil - Google Patents
Determination method for quickly extracting ammonia nitrogen in soil Download PDFInfo
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- CN112014339A CN112014339A CN202010887108.2A CN202010887108A CN112014339A CN 112014339 A CN112014339 A CN 112014339A CN 202010887108 A CN202010887108 A CN 202010887108A CN 112014339 A CN112014339 A CN 112014339A
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/34—Purifying; Cleaning
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/38—Diluting, dispersing or mixing samples
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
Abstract
The invention discloses a determination method for quickly extracting ammonia nitrogen from soil, which comprises the following steps: s1, a pretreatment step; s2, a distillation step; s3, an absorption step; s4, a measuring step; s5, drawing a standard curve; s6, measuring the water content in the soil sample; s7, calculating the content of ammonia nitrogen in the soil sample. The method of the invention adopts a distillation mode to reduce the interference of the chromaticity of the sample, and the reagent is simple, convenient, fast, stable and nontoxic to prepare. The color development is carried out by using the Nar reagent, the color development time is short, and the speed is high.
Description
Technical Field
The invention belongs to the technical field of analytical chemistry, and relates to a determination method for quickly extracting ammonia nitrogen from soil.
Background
In the existing standard of potassium chloride solution extraction-spectrophotometry for measuring ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in HJ634-2012 soil, the ammonia nitrogen in the soil is extracted by using a potassium chloride solution, under an alkaline condition, the ammonia ions of an extracting solution react with phenol in the presence of hypochlorite ions to generate blue indophenol dye, and the blue indophenol dye has maximum absorption at a wavelength of 630 nm. In a certain concentration range, the ammonia nitrogen concentration and the absorbance value accord with the Lambert-beer law. The standard reagent is complex to prepare, and has instability, toxicity and long color development instability time. Some color is leached out from the sample, and the color development is interfered.
Disclosure of Invention
Aiming at the problems, the invention provides a determination method for quickly extracting ammonia nitrogen from soil. The principle is to distill NH4 in soil+By NH3Is released and taken up with boric acid. Ammonia absorbed by boric acid reacts with a nano-reagent in the form of ammonium ions to generate a yellow-brown complex, the chromaticity of the complex is in direct proportion to the content of ammonia nitrogen, and spectrophotometry is carried out at the wavelength of 420 nm.
The determination method of the invention can reduce the interference of the chromaticity of the sample on one hand, and on the other hand, the reagent is simple to prepare, convenient and quick, stable to store for a long time, environment-friendly and nontoxic, and is harmless to human bodies.
The invention refers to the technical scheme of 'GB/T7479-87 colorimetric method for measuring Narse reagent for ammonium water quality', the processed sample is water, wherein, after coagulation precipitation and complexing masking, the sample is still turbid and colored, and a distillation method is needed. The sample treated in the present invention is soil. The invention discloses a pretreatment and distillation method of a soil sample, which proves that the distillation method is also suitable for the soil sample and obtains unexpected technical effects.
The invention discloses a determination method for quickly extracting ammonia nitrogen from soil, which comprises the following steps:
s1, pretreatment: weighing a soil sample, mixing the soil sample with water, and then mixing the soil sample with a treating agent to obtain a mixture for distillation;
s2, a distillation step: distilling the obtained mixture for distillation, NH4 in soil sample+By NH3Is released;
s3, absorption step: absorbing the released NH with an absorbent3Obtaining a test sample for testing;
s4, a measuring step: taking the sample to be tested, mixing the sample with a shielding agent, mixing the sample with a color developing reagent, reacting, and testing absorbance;
s5, drawing a standard curve to obtain the intercept and the efficiency of the standard curve;
s6, determining the moisture content in the soil sample to obtain the dry matter content of the soil sample;
s7, calculating the content of ammonia nitrogen in the soil sample.
In the present invention, NH4 in soil sample is made by distillation+By NH3The form of the compound is released, and after the compound is absorbed by the absorbent, the chromogenic reagents are mixed, reacted and tested for absorbance. The distilled sample has no chromaticity interference, and the influence of color substances in the soil sample on the test absorbance can be reduced.
In the invention, the soil sample is directly mixed with water, and does not need to add KCl solution for leaching or add pH indicator, thus meeting the conditions required by distillation.
In some embodiments of the present invention, in the S1 step, the treating agents are light magnesium oxide and sodium hydroxide.
The light magnesium oxide and the sodium hydroxide in the treating agent are matched with each other, so that the organic nitrogen in a soil sample can be reduced from hydrolysis, and the problem that the result of an ammonia nitrogen result is higher than the actual result is solved.
In some preferred embodiments of the present invention, in the S1 step, the light magnesium oxide and sodium hydroxide account for 2-3% and 4-6% by weight of the soil sample to be tested and the weight ratio of the light magnesium oxide and sodium hydroxide is 1: (1.8-2.2).
The research finds that the light magnesium oxide and the sodium hydroxide have better effect of inhibiting the hydrolysis of the organic nitrogen at the content and the weight ratio.
In some embodiments of the present invention, the amount of water in the S1 step is 150-250ml per 10.00g of the soil sample.
Each 10.00g of the soil sample is mixed with 250ml of water of 150-.
In some embodiments of the present invention, in the S3 step, the absorbent is a boric acid solution having a concentration of 15 to 25 g/L.
At this concentration of the organic acid, the organic acid is dissolved in the solvent,boric acid can completely absorb NH released by distillation3。
In some embodiments of the present invention, in the S4 step, the shielding agent is sodium potassium tartrate.
The sodium potassium tartrate can complex metal ions, and prevent the metal ions from reacting with a color developing agent to develop color and influence the absorbance.
In some embodiments of the invention, the chromogenic agent is a na agent.
The color reagent is a Nashi reagent, and compared with phenol, the reagent is stable and non-toxic, the preparation process is simple, and the storage time is long. The color development is carried out by using the Nar reagent, the color development time is short, and the speed is high.
In some embodiments of the invention, in step S4, the test sample is mixed with sodium potassium tartrate in batches, flocs are formed, the precipitate is removed by centrifugation, and the process is repeated until all the test sample is added, and the absorbance L is measured, wherein the amount V of test sample added in batchesoptThe determination of (a) comprises the steps of:
s31, determining the minimum amount V of sample added for the test that flocculatesmin；
S32, the test specimen is Vmin×1、Vmin×2、Vmin×3、VminThe xI … … is divided into a plurality of parts by a basic unit, i is more than 2;
s33, taking j parts of the test sample for repetition to obtain absorbance Lij;
s34, calculating the final absorbance intra-group variance and inter-group variance between two adjacent grouping basic units,
from small to large, if the absorbance Li between two adjacent basic grouping units has a significant difference, the small basic grouping unit is considered as Vopt。
The amount V of the distillate added per batch determined by this methodoptEither side ofThe number of batch operations is reduced, which in turn reduces the effect of adsorption of the flocs present on the resulting absorbance. The number of batch operations is reduced as much as possible on the premise of accurate results.
In some embodiments of the invention, in the step S5, the weight of the standard ammonia nitrogen product is 0.0, 0.1, 0.2, 0.5, 1.0, 2.0, 3.5ml of 10mg/L ammonia nitrogen product solution.
In the range, the light absorption value of the standard product after color development is linear, and the content of ammonia nitrogen in the soil sample can be calculated.
In some embodiments of the present invention, the calculation formula of the content of ammonia nitrogen in the soil sample is:
wherein the content of the first and second substances,
w-mass fraction of ammonia nitrogen in the soil sample, measured as N, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
The invention has the beneficial technical effects that:
the soil sample pretreatment steps of the invention are simple to operate, the used reagents are few in types, and the prepared mixture can be well distilled.
The method of the invention adopts a distillation mode to reduce the interference of the chromaticity of the sample, and the reagent is simple, convenient, fast, stable and nontoxic to prepare. The color development is carried out by using the Nar reagent, the color development time is short, and the speed is high.
The method has the advantages of stable reagent, no toxicity, simple preparation process and long storage time; the distilled sample has no chroma interference; the color development time is short, and the result calculation process is simple.
In the detection method of the present invention, the detection limit is 0.15mg/kg, and the lower limit of the measurement is 0.6 mg/kg. The detection limit, linearity, recovery rate and precision reach the level of the similar detection methods.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
The following examples and comparative examples are parallel runs, with the same processing steps and parameters, unless otherwise indicated.
Example 1
Pre-treating a soil sample: weighing 10.00g of soil, adding 200ml of distilled water into a 500ml distillation flask, adding 0.25g of light magnesium oxide and 5ml of 100g/L sodium hydroxide, adding 50ml of 20g/L boric acid solution into an absorption flask, connecting a distillation device, ensuring that a condensation pipe is below the absorption liquid level of the boric acid, starting distillation, and collecting 100ml of distillate.
Testing of moisture: another soil sample is taken to be measured according to HJ 613-2011-gravimetric method for measuring dry matters and water in soil ".
And (3) drawing a curve: respectively adding 10mg/L ammonia nitrogen standards of 0.0, 0.1, 0.2, 0.5, 1.0, 2.0 and 3.5ml into 7 colorimetric tubes of 50ml, adding water to a marked line, adding 1ml of potassium sodium tartrate solution and 1ml of a Nashi reagent, uniformly mixing, developing for 10 minutes, taking water as a reference, determining absorbance at 420nm, taking the content of the ammonia nitrogen standard solution as a horizontal coordinate, and taking the corresponding absorbance after blank deduction as a vertical coordinate to draw a standard curve.
The preparation method of the potassium sodium tartrate solution comprises dissolving 50g of potassium sodium tartrate tetrahydrate in 100ml of water, heating to boil, and adding water to a constant volume of 100 ml. The Nassner reagent is a commercial product and can be made by self.
Measurement of the sample: taking 50ml of a sample (if the concentration of the sample is higher, less sample can be taken) in a 50ml colorimetric tube, testing according to the same step of drawing a standard curve, and testing a calculation formula according to the step of measuring the sample in a blank laboratory:
w- - -mass fraction (in N) of ammonia nitrogen in the soil sample, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
Example 2
Pre-treating a soil sample: weighing 10.00g of soil, adding 200ml of distilled water into a 500ml distillation flask, adding 0.20g of light magnesium oxide and 4ml of 100g/L sodium hydroxide, adding 50ml of 20g/L boric acid solution into an absorption flask, connecting a distillation device, ensuring that a condensation pipe is below the absorption liquid level of the boric acid, starting distillation, and collecting 100ml of distillate.
Testing of moisture: another soil sample is taken to be measured according to HJ 613-2011-gravimetric method for measuring dry matters and water in soil ".
And (3) drawing a curve: respectively adding 10mg/L ammonia nitrogen standards of 0.0, 0.1, 0.2, 0.5, 1.0, 2.0 and 3.5ml into 7 colorimetric tubes of 50ml, adding water to a marked line, adding 1ml of potassium sodium tartrate solution and 1ml of a Nashi reagent, uniformly mixing, developing for 10 minutes, taking water as a reference, determining absorbance at 420nm, taking the content of the ammonia nitrogen standard solution as a horizontal coordinate, and taking the corresponding absorbance after blank deduction as a vertical coordinate to draw a standard curve.
The preparation method of the potassium sodium tartrate solution comprises dissolving 50g of potassium sodium tartrate tetrahydrate in 100ml of water, heating to boil, and adding water to a constant volume of 100 ml. The Nassner reagent is a commercial product and can be made by self.
Measurement of the sample: taking 50ml of a sample (if the concentration of the sample is higher, less sample can be taken) in a 50ml colorimetric tube, testing according to the same step of drawing a standard curve, and testing a calculation formula according to the step of measuring the sample in a blank laboratory:
w- - -mass fraction (in N) of ammonia nitrogen in the soil sample, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
Example 3
Pre-treating a soil sample: weighing 10.00g of soil, adding 200ml of distilled water into a 500ml distillation flask, adding 0.30g of light magnesium oxide and 6ml of 100g/L sodium hydroxide, adding 50ml of 20g/L boric acid solution into an absorption flask, connecting a distillation device, ensuring that a condensation pipe is below the absorption liquid level of the boric acid, starting distillation, and collecting 100ml of distillate.
Testing of moisture: another soil sample is taken to be measured according to HJ 613-2011-gravimetric method for measuring dry matters and water in soil ".
And (3) drawing a curve: respectively adding 10mg/L ammonia nitrogen standards of 0.0, 0.1, 0.2, 0.5, 1.0, 2.0 and 3.5ml into 7 colorimetric tubes of 50ml, adding water to a marked line, adding 1ml of potassium sodium tartrate solution and 1ml of a Nashi reagent, uniformly mixing, developing for 10 minutes, taking water as a reference, determining absorbance at 420nm, taking the content of the ammonia nitrogen standard solution as a horizontal coordinate, and taking the corresponding absorbance after blank deduction as a vertical coordinate to draw a standard curve.
The preparation method of the potassium sodium tartrate solution comprises dissolving 50g of potassium sodium tartrate tetrahydrate in 100ml of water, heating to boil, and adding water to a constant volume of 100 ml. The Nassner reagent is a commercial product and can be made by self.
Measurement of the sample: taking 50ml of a sample (if the concentration of the sample is higher, less sample can be taken) in a 50ml colorimetric tube, testing according to the same step of drawing a standard curve, and testing a calculation formula according to the step of measuring the sample in a blank laboratory:
w- - -mass fraction (in N) of ammonia nitrogen in the soil sample, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
Example 4
The difference from example 1 is that the test sample is mixed in portions with sodium potassium tartrate, flocs are formed, the precipitate is removed by centrifugation, and the measurement of the absorbance L is repeated until all the test samples have been added, wherein the amount V of the test sample added in portions is measuredoptThe determination of (a) comprises the steps of:
s31, determination of minimum occurrence of flocsAmount of sample added Vmin；
S32, the test specimen is Vmin×1、Vmin×2、Vmin×3、VminThe xI … … is divided into a plurality of parts by a basic unit, i is more than 2;
s33, taking j parts of the test sample for repetition to obtain absorbance Lij;
s34, calculating the final absorbance intra-group variance and inter-group variance between two adjacent grouping basic units,
from small to large, if the absorbance Li between two adjacent basic grouping units has a significant difference, the small basic grouping unit is considered as Vopt。
The amount V of the distillate added per batch determined by this methodoptThe number of batch operations is reduced, as well as the effect of the adsorption of the flocs present on the resulting absorbance. The number of batch operations is reduced as much as possible on the premise of accurate results.
Comparative example 1
Pre-treating a soil sample: weighing 10.00g of soil, adding 200ml of distilled water into a 500ml distillation flask, adding 0.50g of light magnesium oxide and 5ml of 100g/L sodium hydroxide, adding 50ml of 20g/L boric acid solution into an absorption flask, connecting a distillation device, ensuring that a condensation pipe is below the absorption liquid level of the boric acid, starting distillation, and collecting 100ml of distillate.
Testing of moisture: another soil sample is taken to be measured according to HJ 613-2011-gravimetric method for measuring dry matters and water in soil ".
And (3) drawing a curve: respectively adding 10mg/L ammonia nitrogen standards of 0.0, 0.1, 0.2, 0.5, 1.0, 2.0 and 3.5ml into 7 colorimetric tubes of 50ml, adding water to a marked line, adding 1ml of potassium sodium tartrate solution and 1ml of a Nashi reagent, uniformly mixing, developing for 10 minutes, taking water as a reference, determining absorbance at 420nm, taking the content of the ammonia nitrogen standard solution as a horizontal coordinate, and taking the corresponding absorbance after blank deduction as a vertical coordinate to draw a standard curve.
The preparation method of the potassium sodium tartrate solution comprises dissolving 50g of potassium sodium tartrate tetrahydrate in 100ml of water, heating to boil, and adding water to a constant volume of 100 ml. The Nassner reagent is a commercial product and can be made by self.
Measurement of the sample: taking 50ml of a sample (if the concentration of the sample is higher, less sample can be taken) in a 50ml colorimetric tube, testing according to the same step of drawing a standard curve, and testing a calculation formula according to the step of measuring the sample in a blank laboratory:
w- - -mass fraction (in N) of ammonia nitrogen in the soil sample, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
Comparative example 2
Pre-treating a soil sample: weighing 10.00g of soil, adding 200ml of distilled water into a 500ml distillation flask, adding 0.20g of light magnesium oxide and 6ml of 100g/L sodium hydroxide, adding 50ml of 20g/L boric acid solution into an absorption flask, connecting a distillation device, ensuring that a condensation pipe is below the absorption liquid level of the boric acid, starting distillation, and collecting 100ml of distillate.
Testing of moisture: another soil sample is taken to be measured according to HJ 613-2011-gravimetric method for measuring dry matters and water in soil ".
And (3) drawing a curve: respectively adding 10mg/L ammonia nitrogen standards of 0.0, 0.1, 0.2, 0.5, 1.0, 2.0 and 3.5ml into 7 colorimetric tubes of 50ml, adding water to a marked line, adding 1ml of potassium sodium tartrate solution and 1ml of a Nashi reagent, uniformly mixing, developing for 10 minutes, taking water as a reference, determining absorbance at 420nm, taking the content of the ammonia nitrogen standard solution as a horizontal coordinate, and taking the corresponding absorbance after blank deduction as a vertical coordinate to draw a standard curve.
The preparation method of the potassium sodium tartrate solution comprises dissolving 50g of potassium sodium tartrate tetrahydrate in 100ml of water, heating to boil, and adding water to a constant volume of 100 ml. The Nassner reagent is a commercial product and can be made by self.
Measurement of the sample: taking 50ml of a sample (if the concentration of the sample is higher, less sample can be taken) in a 50ml colorimetric tube, testing according to the same step of drawing a standard curve, and testing a calculation formula according to the step of measuring the sample in a blank laboratory:
w- - -mass fraction (in N) of ammonia nitrogen in the soil sample, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
Comparative example 3
Pre-treating a soil sample: weighing 10.00g of soil, adding 200ml of distilled water into a 500ml distillation flask, adding 0.25g of light magnesium oxide and 140g/L of potassium hydroxide into the distillation flask, adding 50ml of 20g/L boric acid solution into an absorption flask, connecting a distillation device, ensuring that a condensation pipe is below the absorption liquid level of the boric acid, starting distillation, and collecting 100ml of distillate.
Testing of moisture: another soil sample is taken to be measured according to HJ 613-2011-gravimetric method for measuring dry matters and water in soil ".
And (3) drawing a curve: respectively adding 10mg/L ammonia nitrogen standards of 0.0, 0.1, 0.2, 0.5, 1.0, 2.0 and 3.5ml into 7 colorimetric tubes of 50ml, adding water to a marked line, adding 1ml of potassium sodium tartrate solution and 1ml of a Nashi reagent, uniformly mixing, developing for 10 minutes, taking water as a reference, determining absorbance at 420nm, taking the content of the ammonia nitrogen standard solution as a horizontal coordinate, and taking the corresponding absorbance after blank deduction as a vertical coordinate to draw a standard curve.
The preparation method of the potassium sodium tartrate solution comprises dissolving 50g of potassium sodium tartrate tetrahydrate in 100ml of water, heating to boil, and adding water to a constant volume of 100 ml. The Nassner reagent is a commercial product and can be made by self.
Measurement of the sample: taking 50ml of a sample (if the concentration of the sample is higher, less sample can be taken) in a 50ml colorimetric tube, testing according to the same step of drawing a standard curve, and testing a calculation formula according to the step of measuring the sample in a blank laboratory:
w- - -mass fraction (in N) of ammonia nitrogen in the soil sample, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
Examples of the experiments
1 Effect of the treating agent
Taking the absorbance values obtained in the experimental examples and the comparative examples, the comparative examples are significantly higher than the examples based on the lowest value of the examples, and the results are shown in table 1.
TABLE 1 Effect of treatment Agents
| Absorbance/relative value | |
| Example 1 | 100a |
| Example 2 | 102a |
| Example 3 | 103a |
| Comparative example 1 | 115b |
| Comparative example 2 | 121c |
| Comparative example 3 | 112b |
In the table, the lower case letters are different, indicating that the difference is significant (P is less than 0.05)
Organic nitrogen in the soil sample is decomposed into ammonia during distillation under alkaline conditions, so that the actual content of ammonia nitrogen in the sample is influenced. As can be seen from Table 1, in the method of the present invention, the decomposition rate of organic nitrogen is less than 3% by controlling the amounts of the treating agents, i.e., light magnesium oxide and sodium hydroxide. In contrast, in the comparative test using the treating agent in an amount exceeding the above-mentioned weight ratio, the decomposition rate of organic nitrogen was about 15%, for example, in comparative example 1, and in some cases, it reached about 21%, for example, in comparative example 2, significantly higher than 3%. Meanwhile, in comparative example 3 in which the same molar equivalent of potassium hydroxide was used instead of sodium hydroxide, a similar technical effect, which was about 10% higher, could not be obtained.
Time repeatability in 2 embodiment
In order to eliminate the influence of the distillation time among the influences of the above-mentioned treatment agents and avoid the case where the absorbance value is increased due to incomplete distillation in the soil sample, the change of absorbance with the distillation time was examined in example 1 and comparative example 1.
In example 1 and comparative example 1, the time for distillation was extended by 10%, 30% and 50%, respectively, and the change in absorbance was examined. The results are shown in Table 2.
TABLE 2 influence of distillation time
As can be seen from table 2, in the distillation methods of example 1 and comparative example 1 of the present invention, the absorbance did not significantly change with the extension of the distillation time, indicating that ammonia nitrogen in the soil sample did not remain and the distillation time was not the cause of the above difference.
While the preferred embodiments and examples of the present invention have been described in detail, the present invention is not limited to the embodiments and examples, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (10)
1. A determination method for quickly extracting ammonia nitrogen from soil comprises the following steps:
s1, pretreatment: weighing a soil sample, mixing the soil sample with water, and then mixing the soil sample with a treating agent to obtain a mixture for distillation;
s2, a distillation step: distilling the obtained mixture for distillation, NH4 in soil sample+By NH3Is released;
s3, absorption step: absorbing the released NH with an absorbent3Obtaining a test sample for testing;
s4, a measuring step: taking the sample to be tested, mixing the sample with a shielding agent, mixing the sample with a color developing reagent, reacting, and testing absorbance;
s5, drawing a standard curve to obtain the intercept and the efficiency of the standard curve;
s6, determining the moisture content in the soil sample to obtain the dry matter content of the soil sample;
s7, calculating the content of ammonia nitrogen in the soil sample.
2. The method of claim 1, wherein in the step of S1, the treating agents are light magnesium oxide and sodium hydroxide.
3. The method according to claim 2, wherein in the step of S1, the weight percentages of the light magnesium oxide and the sodium hydroxide in the soil sample to be tested are 2-3% and 4-6%, and the weight ratio of the light magnesium oxide and the sodium hydroxide is 1: (1.8-2.2).
4. The method as claimed in claim 1, wherein the amount of water used in the step S1 is 150-250ml per 10.00g of the soil sample.
5. The method according to claim 1, wherein in the step of S3, the absorbent is a boric acid solution, and the concentration of the boric acid solution is 15-25 g/L.
6. The method of claim 1, wherein in the step of S4, the shielding agent is sodium potassium tartrate.
7. The method according to claim 1, wherein in the step of S4, the color developing agent is a na reagent.
8. The method of claim 1, wherein in step S4, the test sample is mixed with sodium potassium tartrate in batches, flocculated, centrifuged to remove precipitates, and repeated until all the test sample is added, and absorbance L is measured, wherein the test sample is added in batches in an amount VoptThe determination of (a) comprises the steps of:
s31, determining the minimum amount V of sample added for the test that flocculatesmin；
S32, the test specimen is Vmin×1、Vmin×2、Vmin×3、VminThe xI … … is divided into a plurality of parts by a basic unit, i is more than 2;
s33, taking j parts of the test sample for repetition to obtain absorbance Lij;
s34, calculating the final absorbance intra-group variance and inter-group variance between two adjacent grouping basic units,
from small to large, if the absorbance Li between two adjacent basic grouping units has a significant difference, the small basic grouping unit is considered as Vopt。
9. The method according to claim 1, wherein in the step S5, the weight of the ammonia nitrogen standard substance comprises taking 0.0, 0.1, 0.2, 0.5, 1.0, 2.0 and 3.5ml of 10mg/L ammonia nitrogen standard substance solution.
10. The method according to claim 1, wherein in the step of S7, the calculation formula for calculating the content of ammonia nitrogen in the soil sample is as follows:
wherein the content of the first and second substances,
w-mass fraction of ammonia nitrogen in the soil sample, measured as N, mg/kg;
a- - -absorbance value of the sample;
a0- -absorbance of blank sample;
a- -intercept of the standard curve;
v1- -volume of distillate, 100 ml;
v2- -colorimetric sample volume ml;
b- -slope of the standard curve;
m-mass of the sample g;
Wdm-dry matter content,% -of soil sample.
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