CN112051253A - Method and device for measuring nitrate nitrogen content of soil - Google Patents
Method and device for measuring nitrate nitrogen content of soil Download PDFInfo
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- 239000002689 soil Substances 0.000 title claims abstract description 209
- MMDJDBSEMBIJBB-UHFFFAOYSA-N [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] Chemical compound [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] MMDJDBSEMBIJBB-UHFFFAOYSA-N 0.000 title claims abstract description 114
- 238000000034 method Methods 0.000 title claims abstract description 60
- 239000003011 anion exchange membrane Substances 0.000 claims abstract description 91
- 238000001228 spectrum Methods 0.000 claims abstract description 60
- 238000001514 detection method Methods 0.000 claims abstract description 53
- 238000002156 mixing Methods 0.000 claims abstract description 31
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 27
- 239000008213 purified water Substances 0.000 claims abstract description 18
- 238000001035 drying Methods 0.000 claims abstract description 16
- 238000011282 treatment Methods 0.000 claims abstract description 10
- 238000004140 cleaning Methods 0.000 claims abstract description 6
- 230000003595 spectral effect Effects 0.000 claims description 28
- 238000001237 Raman spectrum Methods 0.000 claims description 22
- 238000005259 measurement Methods 0.000 claims description 21
- 238000011065 in-situ storage Methods 0.000 claims description 18
- 238000003825 pressing Methods 0.000 claims description 18
- 238000001069 Raman spectroscopy Methods 0.000 claims description 16
- 238000003756 stirring Methods 0.000 claims description 15
- 239000012528 membrane Substances 0.000 claims description 14
- 238000012545 processing Methods 0.000 claims description 12
- 230000005284 excitation Effects 0.000 claims description 10
- 239000002245 particle Substances 0.000 claims description 9
- 238000006073 displacement reaction Methods 0.000 claims description 8
- 238000005342 ion exchange Methods 0.000 claims description 6
- 238000007781 pre-processing Methods 0.000 claims description 6
- 241000196324 Embryophyta Species 0.000 claims description 5
- 239000011248 coating agent Substances 0.000 claims description 5
- 238000000576 coating method Methods 0.000 claims description 5
- 238000011088 calibration curve Methods 0.000 claims description 4
- 238000000691 measurement method Methods 0.000 claims description 4
- 230000008569 process Effects 0.000 abstract description 15
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- 230000004044 response Effects 0.000 abstract description 4
- 238000012544 monitoring process Methods 0.000 abstract description 3
- 239000000243 solution Substances 0.000 description 33
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 229910002651 NO3 Inorganic materials 0.000 description 8
- 238000002329 infrared spectrum Methods 0.000 description 8
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 6
- 230000003993 interaction Effects 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 239000002002 slurry Substances 0.000 description 5
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- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 150000003863 ammonium salts Chemical class 0.000 description 2
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- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 description 2
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- 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
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/12—Generating the spectrum; Monochromators
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/44—Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
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- Analytical Chemistry (AREA)
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Abstract
The embodiment of the invention provides a method and a device for measuring the content of nitrate nitrogen in soil, wherein the method for measuring the content of nitrate nitrogen in soil comprises the following steps: s1, mixing a soil sample with a preset amount with purified water in proportion to prepare a soil solution; s2, mixing the prepared anion exchange membrane with a soil solution for a preset time, and then sequentially carrying out purified water cleaning and drying treatment on the anion exchange membrane; s3, performing spectrum detection on the nitrate nitrogen enriched on the dried anion exchange membrane, and calculating the content of the nitrate nitrogen in the soil sample based on characteristic spectrum intensity information obtained by the spectrum detection; the method is convenient to operate, high in integration level in the whole test operation process, low in professional requirements on test processes and technicians, capable of realizing on-site rapid detection without chemical reagents participating in extraction of target objects, and significant in timely monitoring of soil nutrients in a field and rapid response of soil non-point source pollution possibly caused by excessive fertilization.
Description
Technical Field
The invention relates to the field of farmland soil non-point source pollution detection, in particular to a method and a device for measuring soil nitrate nitrogen content.
Background
Nitrate nitrogen refers to nitrogen elements contained in nitrate. The organic matters in the water and the soil are decomposed to generate ammonium salt, and the ammonium salt is changed into nitrate nitrogen after being oxidized. Nitrate nitrogen is used for supplementing nitrogen elements in agriculture, so that the growth of crops is accelerated, and the growth period and the harvesting period of the crops are prolonged. The nitrogen deficiency of crops can cause fruit dysplasia and more malformed fruits, and correspondingly, fertilizers such as potassium nitrate and the like play a vital role in the growth of crops and belong to one of three essential nutrient elements for the growth of crops.
As the nitrate nitrogen in the soil has negative charges as the same as soil colloids and is not easy to be adsorbed by the soil colloids, the nitrate nitrogen is an important component of the quick-acting nitrogen fertilizer and is an important nutrient substance which can be directly absorbed by plants, and the content of the nitrate nitrogen in the soil is also one of important indexes for measuring the soil fertility. However, the nitrification and denitrification in the circulation process of nitrogen in soil not only results in the loss of nitrogen, but also may cause the problems of soil non-point source pollution and the like due to excessive fertilization, and therefore, the method has important significance for the measurement of soil nitrate nitrogen.
In the prior art, methods for measuring the nitrate in the soil comprise an ultraviolet spectrophotometry method, a flow injection method, an ion chromatography method, an ion selective electrode method and the like. The determination methods are required to be carried out in a laboratory and cannot be used for field operation, particularly for an ultraviolet spectrophotometry method, a flow injection method and an ion chromatography, soil samples are required to be sieved and ground before treatment, and operations such as chemical reagent leaching and filtering are required to be carried out during measurement.
In the existing patent literature, a soil nitrate nitrogen rapid measurement device based on infrared spectrum and a use method thereof are disclosed, wherein an infrared ATR accessory is adopted to measure soil pasty mud so as to obtain the content of nitrate nitrogen in soil. The measurement principle of the method is based on the interaction of infrared light on the surface of the corresponding crystal of the infrared ATR accessory and soil pasty slurry, so that the particle size of an original soil sample and the mixing ratio of the original soil sample and water need to be strictly controlled in the measurement process, the original soil sample is ensured to be prepared into a slurry state and is tightly attached to the surface of the corresponding crystal of the infrared ATR accessory, and the measurement accuracy can be ensured.
In another patent document, a soil nitrate nitrogen leaching agent and a soil nitrate nitrogen rapid determination method are disclosed, the measurement method introduces chemical reagents to carry out treatments such as leaching, color development and titration in the determination of soil nitrate nitrogen, and adopts a colorimetric/ultraviolet absorption method to realize, the operation process is complex, the requirement on the professional of testers is high, a laboratory analysis instrument is required to be matched for carrying out related analysis tests, and the method is not suitable for field application.
Therefore, the existing method for measuring nitrate nitrogen in soil generally has strong indoor limitation, strict sample processing requirement, complex operation, need of chemical reagents, and risk of secondary pollution of the chemical reagents in measurement.
Disclosure of Invention
The embodiment of the invention provides a method and a device for measuring the content of nitrate nitrogen in soil, which are used for solving the problems of strong indoor limitation, strict sample treatment, complex operation and secondary pollution risk of chemical reagents in the existing method for measuring nitrate nitrogen in soil.
The embodiment of the invention provides a method for measuring the content of nitrate nitrogen in soil, which comprises the following steps: s1, mixing a soil sample with a preset amount with purified water in proportion to prepare a soil solution; s2, mixing the prepared anion exchange membrane with the soil solution for a preset time, and then sequentially carrying out purified water cleaning and drying treatment on the anion exchange membrane; and S3, performing spectrum detection on the nitrate nitrogen enriched on the dried anion exchange membrane, and calculating the content of the nitrate nitrogen in the soil sample based on the characteristic spectrum intensity information obtained by the spectrum detection.
According to the soil nitrate nitrogen content measuring method of one embodiment of the present invention, the mixing the prepared anion-exchange membrane with the soil solution in S2, further includes: and (2) placing the anion exchange membrane in the soil solution, and adopting an oscillator or a stirrer to assist the anion exchange membrane to be in full contact and mixed with the soil solution.
According to the method for measuring the content of nitrate nitrogen in soil, in S3, the performing a spectrum detection on the nitrate nitrogen enriched on the anion exchange membrane after the drying treatment further includes: s31, enabling laser with preset wavelength to be incident on the surface of the anion exchange membrane, and obtaining scattered light scattered by nitrate nitrogen on the anion exchange membrane; s32, performing spectrum detection on the scattered light through a Raman spectrum detection module to obtain Raman spectrum intensities of the scattered light at different spectrum shifts; and S33, preprocessing the Raman spectrum intensities at different spectrum displacement positions to obtain the spectrum intensity of the nitrate nitrogen at the Raman spectrum characteristic position.
According to the method for measuring the content of nitrate nitrogen in soil, in S3, the obtaining the content of nitrate nitrogen in the soil sample based on the characteristic spectrum intensity information obtained by the spectrum detection further includes: combining the characteristic spectrum intensity information with a pre-established calibration model to obtain the content of nitrate nitrogen in the soil sample; the calibration model is a calibration curve which is established in advance based on a standard soil sample corresponding to the soil sample and represents the correlation between the nitrate nitrogen content of the standard soil sample and the spectral intensity of nitrate nitrogen at the Raman spectral characteristic position.
According to the soil nitrate nitrogen content measuring method of one embodiment of the present invention, S1 further includes an operation of acquiring the soil sample: digging in-situ soil at a preset depth of a preset position, removing large particles and weeds in the in-situ soil, drying the in-situ soil, and taking the dried in-situ soil as the soil sample.
According to the method for measuring the content of nitrate nitrogen in soil, the exchange groups of the anion exchange membrane comprise OH-Or Cl-。
The embodiment of the invention also provides a measuring device of the method for measuring the content of nitrate nitrogen in soil, which comprises the following steps: the soil sample mixing assembly is used for containing a soil solution prepared from a soil sample; the anion exchange membrane is used for carrying out ion exchange with nitrate nitrogen in the soil solution; the scattered light collection device is used for carrying out laser excitation on the nitrate nitrogen enriched on the anion exchange membrane so as to output scattered light; the spectrum detection module is used for acquiring characteristic spectrum intensity information of the scattered light; and the processing module is used for acquiring the content of the nitrate nitrogen in the soil sample based on the characteristic spectrum intensity information.
According to the measuring device of one embodiment of the invention, the soil sample mixing assembly comprises a container provided with a stirring device and/or a vibrator, wherein a stirring end of the stirring device extends into the container, and the vibrator is used for placing the container.
According to the measuring device of one embodiment of the invention, the anion exchange membrane is provided with a membrane fixing frame, the membrane fixing frame comprises a first pressing sheet and a second pressing sheet, the first pressing sheet and the second pressing sheet are provided with corresponding windows, and the anion exchange membrane is clamped between the first pressing sheet and the second pressing sheet.
According to a measuring apparatus of an embodiment of the present invention, the scattered light collecting apparatus includes: the laser generator is used for outputting laser with a preset wavelength; the coating surface of the spectroscope is used for receiving the laser output by the laser generator and reflecting the laser to the surface of the anion exchange membrane, and correspondingly, the scattered light scattered by the nitrate nitrogen on the anion exchange membrane is also transmitted to the spectrum detection module through the spectroscope.
According to the measuring apparatus of an embodiment of the present invention, the scattered light collecting apparatus further includes: the focusing lens is used for focusing the laser reflected by the coating surface of the spectroscope to the surface of the anion exchange membrane, and correspondingly, the focusing lens is also used for focusing the scattered light scattered by the nitrate nitrogen on the anion exchange membrane and then transmitting the scattered light to the spectrum detection module through the spectroscope; and/or the optical filter is used for carrying out filtering processing on the light beam transmitted to the spectrum detection module by the spectroscope.
According to the method and the device for measuring the nitrate nitrogen content of the soil, provided by the embodiment of the invention, the soil solution can be obtained by mixing the soil sample with the preset amount of purified water in proportion, the prepared anion exchange membrane is mixed with the soil solution, so that the anion exchange membrane and nitrate ions in the soil solution can be subjected to exchange reaction, and after the preset time, the purpose of extracting the nitrate nitrogen in the soil sample can be achieved, so that the anion exchange membrane sample is prepared after the anion exchange membrane subjected to the exchange reaction is sequentially subjected to purified water cleaning and drying treatment, the nitrate nitrogen enriched on the anion exchange membrane sample can be subjected to spectrum detection, and the nitrate nitrogen content in the soil sample can be conveniently obtained based on the correlation between the obtained characteristic spectrum intensity information and the nitrate nitrogen content in the soil.
Therefore, the method is convenient and fast to operate, the content of the nitrate nitrogen in the soil sample can be accurately and quickly obtained in a spectral detection mode on site after the nitrate nitrogen in the soil sample is extracted by the membrane, the integration level of the whole test operation process is high, the requirements on the test flow and the professional of technicians are not high, and a chemical reagent is not required to participate in the extraction of a target object in the test, so that the hidden danger of secondary pollution of the chemical reagent in the measurement is effectively solved, the site quick detection can be realized, and the method has important significance for timely monitoring of soil nutrients in a field and quick response of soil non-point source pollution possibly caused by excessive fertilization.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method for measuring the content of nitrate nitrogen in soil according to an embodiment of the invention;
FIG. 2 shows soil samples with different nitrate nitrogen contents in 1040cm displacement according to the embodiment of the present invention-1(ii) Raman spectral intensity profile of (ii);
FIG. 3 is a schematic structural diagram of a measuring device based on a soil nitrate nitrogen content measuring method (not including a soil sample mixing component) according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a soil sample mixing assembly provided by an embodiment of the present invention;
fig. 5 is a schematic view of an installation structure of an anion exchange membrane provided in an embodiment of the present invention.
In the figure, 1, a soil sample mixing assembly; 11. a container; 12. a stirring device; 13. an oscillator; 14. a mounting structure; 2. an anion exchange membrane; 3. a scattered light collection means; 31. a laser generator; 32. a beam splitter; 33. a focusing lens; 34. a reflective mirror; 35. an optical filter; 4. a spectrum detection module; 5. a processing module; 6. a human-computer interaction module; 7. a membrane holder.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without any inventive step, are within the scope of the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Referring to fig. 1, the present embodiment provides a method for measuring nitrate nitrogen content in soil, including: s1, mixing a soil sample with a preset amount with purified water in proportion to prepare a soil solution; s2, mixing the prepared anion exchange membrane with a soil solution for a preset time, and then sequentially carrying out purified water cleaning and drying treatment on the anion exchange membrane; and S3, performing spectrum detection on the nitrate nitrogen enriched on the dried anion exchange membrane, and calculating the content of the nitrate nitrogen in the soil sample based on the characteristic spectrum intensity information obtained by the spectrum detection.
Specifically, according to the measurement method shown in this embodiment, a soil solution can be obtained by mixing a soil sample with a preset amount of purified water in a ratio, and the prepared anion exchange membrane is mixed with the soil solution, so that an exchange reaction can be performed between the anion exchange membrane and nitrate ions in the soil solution, and after a preset time, the purpose of extracting nitrate nitrogen in the soil sample can be achieved.
Therefore, the measurement method shown in the embodiment is convenient and fast to operate, the content of the nitrate nitrogen in the soil sample can be accurately and quickly obtained in a spectral detection mode on site after the nitrate nitrogen in the soil sample is extracted by a membrane, the integration level of the whole test operation process is high, the requirements on the test flow and the professional performance of technicians are not high, and a chemical reagent is not required to participate in the extraction of a target object in the test, so that the potential hazard of secondary pollution of the chemical reagent in the measurement is effectively solved, the site quick detection can be realized, and the method has important significance for timely monitoring of soil nutrients in a field and quick response of soil area source pollution possibly caused by excessive fertilization.
It should be noted that, since the present embodiment is based on membrane extraction of nitrate nitrogen in a soil sample, and then performing spectrum detection to obtain the content of nitrate nitrogen in the soil sample, the spectrum detection shown in the present embodiment can not only adopt raman spectrum detection as shown in the following embodiment, but also adopt infrared spectrum detection known in the art, which can ensure the accuracy of obtaining detection data by infrared spectrum detection and simplify the data processing process.
In the existing patent documents, no matter the publication No. CN106770058A 'fast special device and its using method for soil nitrate nitrogen based on infrared spectrum' or the patent No. US10345283B1 'a vehicle-mounted method for measuring soil nitrate nitrogen based on FTIR-ATR' are to closely contact the soil sample with the crystal surface corresponding to the ATR accessory, and then adopt infrared spectrum detection to obtain the content of soil nitrate nitrogen. In this case, the soil-water mixing ratio of the soil sample needs to be strictly controlled so that the soil sample is in a slurry state, otherwise, the soil sample is difficult to contact with the corresponding crystal of the ATR accessory well, and meanwhile, the soil sample in the slurry state or the original soil sample contains soluble or insoluble carbonate in the soil, especially for the insoluble carbonate, the infrared spectrum peak of the soil sample has cross coverage interference on the infrared characteristic spectrum peak of nitrate, and the characteristic peak of nitrate is completely covered in severe cases. On the contrary, the scheme shown in the embodiment performs infrared spectrum detection on the basis of nitrate nitrogen film extraction, so that the problem can be well avoided.
Although there are some common problems with infrared spectroscopy, such as: during the measurement process, the detector needs internal refrigeration to ensure the stable response of the detector; meanwhile, water has strong absorption on the infrared spectrum, so that the detection result is greatly influenced by the water; in addition, in carrying out infrared spectroscopy, all need to carry out background sampling before every sample measurement, but the spectral measurement that this embodiment was carried out to the anion exchange membrane sample of preparation can partially avoid the problem that current infrared spectroscopy detected and exists, compares in the infrared spectroscopy measurement mode of current soil nitrate nitrogen, in the measurement process, need not strictly control soil, water ratio and need not to carry out the grinding that becomes more meticulous to soil etc to reduce the degree of difficulty of measurement operation greatly, improved measuring speed, the accuracy of measurement is also showing and is promoted.
Preferably, in S1 shown in this embodiment, when the soil sample is obtained, the specific operations adopted include: the method comprises the steps of digging in-situ soil at a preset depth of a preset position, removing large particles and weeds in the in-situ soil in a manual screening or screen screening mode, drying the in-situ soil in a drying or natural air convection mode to prevent errors caused by the water content in the in-situ soil to the ratio of soil and water, and taking the in-situ soil after drying as a soil sample. The large particle shown in this embodiment refers to a particle with a particle size significantly larger than that of most soil powders in-situ soil, and such large particle may be stones, soil polymers, soil and stone polymers, etc. commonly found in-situ soil.
Preferably, in the embodiment, a soil sample with a preset amount is mixed with purified water in proportion, which is to be understood as that the soil sample is mixed with the purified water according to a certain mass ratio, for example: 5g of soil sample can be weighed by an electronic scale, and the soil solution can be prepared by mixing 5g of soil sample with 25mL of pure water according to the proportion of 1: 5.
In addition, the exchange groups of the anion exchange membrane shown in this example include OH-Or Cl-Thus, in the anion exchange membrane and the soil solutionWhen mixed, can pass through OH on an anion exchange membrane-Or Cl-With NO in soil solution3 -Exchange takes place to realize NO3 -Transfer and enrichment from the soil to the surface of the anion exchange membrane.
It should be noted here that in practice, anion exchange membranes of different manufacturers may have different exchange capacities, i.e. exchangeable ion capacity per unit mass of anion exchange membrane, generally expressed as exchange equivalent meq/g, and the total amount of exchangeable ions may be characterized by exchange capacity/anion valence, e.g. when the exchange capacity of the anion exchange membrane is 2meq/g, it indicates exchangeable 1-valent anions (NO) per 1g of anion exchange membrane (NO)3 -) In a total amount of 2mol, exchangeable anions having a valency of 2 (SO)4 2-) The total amount of (b) is accordingly 1 mol. Therefore, the dosage of the anion exchange membrane needs to be adjusted by combining the ion exchange capacity of the anion exchange membrane so as to adapt to soil samples of different nitrate nitrogen, and corresponding models are established according to different anion exchange membranes.
Preferably, in S2 shown in this embodiment, the mixing the prepared anion-exchange membrane with the soil solution further includes: arrange anion exchange membrane in soil solution, adopt oscillator or agitator to assist anion exchange membrane and soil solution's abundant contact mixture, so can ensure that the equal soil solution of each region on anion exchange membrane surface contacts in the short time to carry out the membrane exchange reaction, can effectively improve the efficiency of membrane exchange, thereby reduced the time of whole test procedure greatly.
Preferably, in this embodiment, in S3, the performing a spectroscopic detection on the nitrate nitrogen enriched on the anion-exchange membrane after the drying treatment further includes: s31, enabling laser with preset wavelength to be incident on the surface of the anion exchange membrane, and obtaining scattered light scattered by nitrate nitrogen on the anion exchange membrane; s32, performing spectrum detection on the scattered light through a Raman spectrum detection module to obtain Raman spectrum intensities of the scattered light at different spectral displacement positions; and S33, preprocessing the Raman spectrum intensities at different spectrum displacement positions to obtain the spectrum intensity of the nitrate nitrogen at the Raman spectrum characteristic position.
Specifically, in S31 shown in this embodiment, the laser incident on the anion exchange membrane is excitation laser, the preset wavelength selected by the excitation laser may be 532nm, 633nm, and 785nm, and the preset wavelength is specifically selected adaptively according to the actually adopted soil sample.
Meanwhile, in S33 shown in this embodiment, the preprocessing of the Raman spectrum intensities at different spectral shifts includes: the processing module is adopted to carry out spectrum preprocessing such as multiple sampling averaging, denoising, smoothing and the like to obtain NO3 -The group is displaced at 1040cm-1Raman spectral intensity of (d).
As shown in FIG. 2, in the distribution diagram of Raman spectral intensity (also referred to as Raman spectral intensity), the shift shown on the abscissa is 1040cm-1The position of the position is characterized by the characteristic position of nitrate nitrogen in the Raman spectrum, the abscissa shown in FIG. 2 is wave number, and the displacement of the Raman spectrum is characterized and expressed in cm-1The Raman spectral intensity is normalized on the ordinate.
As shown in fig. 2, this embodiment specifically plots nine Raman spectral intensity distribution curves, each having the maximum normalized Raman spectral intensity at a Raman spectral feature position, and as the content of nitrate nitrogen in the soil sample increases, i.e., in fig. 2, the content of nitrate nitrogen gradually increases from 20mg/kg to 200mg/kg, and the corresponding normalized Raman spectral intensity at the Raman spectral feature position also gradually increases accordingly.
Therefore, when the content of the nitrate nitrogen in the soil sample is obtained through the spectral intensity, a calibration model can be established in advance, the calibration model is a calibration curve established in advance based on a standard soil sample corresponding to the soil sample, the calibration curve represents the correlation between the nitrate nitrogen content of the standard soil sample and the spectral intensity of the nitrate nitrogen at the Raman spectral characteristic position, and after the spectral intensity of the nitrate nitrogen at the Raman spectral characteristic position is obtained in S32, the characteristic spectral intensity information can be combined with the pre-established calibration model to obtain the content of the nitrate nitrogen in the soil sample.
It should be noted here that in the actual measurement, for soil samples with different nitrate nitrogen contents, different measuring ranges can be adapted by adjusting the soil sample dosage and the membrane dosage, so as to avoid the nitrate nitrogen content of the actually unknown soil sample from exceeding the corresponding quantitative detection range.
As shown in fig. 3, this embodiment further provides a measuring device of the method for measuring the content of nitrate nitrogen in soil as described above, including: the soil sample mixing assembly 1 is used for containing a soil solution prepared from a soil sample; the anion exchange membrane 2 is used for carrying out ion exchange with nitrate nitrogen in the soil solution; the scattered light acquisition device 3 is used for carrying out laser excitation on nitrate nitrogen enriched on the anion exchange membrane 2 so as to output scattered light; the spectrum detection module 4 is used for acquiring characteristic spectrum intensity information of the scattered light; and the processing module 5 is used for calculating the content of nitrate nitrogen in the soil sample based on the acquired characteristic spectrum intensity information.
The following describes the operation flow of the measuring apparatus shown in this embodiment with reference to one of the specific embodiments as follows:
(1) sampling, namely digging a certain amount of in-situ soil at a preset position and a preset depth in a field, screening out impurities such as large particles, weeds and the like in the in-situ soil through an 8-mesh screen, drying the in-situ soil to obtain a soil sample, and weighing 5g of the soil sample by using a small electronic scale;
(2) mixing, according to the dosage of the soil sample, according to the ratio of 1:5 proportion, metering 25mL of purified water, preparing the required soil solution in the soil sample mixing component 1, adding the anion exchange membrane 2 into the soil sample mixing component 1, and fully contacting and mixing the anion exchange membrane 2 and the soil solution so as to carry out ion exchange between the anion exchange membrane 2 and nitrate nitrogen in the soil solution, so that NO in the soil solution is exchanged3 -Transfer and enrichment on the surface of the anion exchange membrane 2;
(3) cleaning and drying, washing soil slurry attached to the surface of the anion exchange membrane 2 by using purified water, and then naturally drying for 2-5 minutes;
(4) measuring, performing laser excitation on nitrate nitrogen enriched on the dried anion exchange membrane 2 by adopting a scattered light acquisition device 3 to output scattered light, performing spectrum detection on the scattered light by adopting a spectrum detection module 4 to obtain the Raman spectrum intensities of the scattered light at different spectrum displacement positions, preprocessing the Raman spectrum intensities at different spectrum displacement positions to obtain the spectrum intensity of nitrate nitrogen at the Raman spectrum characteristic position, calculating and obtaining the content of nitrate nitrogen in an actual soil sample by combining a calibration model which is pre-established through a standard soil sample, and further performing real-time display through a man-machine interaction module 6.
It should be noted that the light beam output by the scattered light collecting device 3 shown in this embodiment is transmitted to the spectrum detecting module 4, the spectrum detecting module 4 is in communication connection with the processing module 5, and the scattered light collecting device 3, the spectrum detecting module 4 and the processing module 5 are all in communication connection with the human-computer interaction module 6, where the spectrum detecting module 4 may be a Raman spectrum detector known in the art, the processing module 5 may be an industrial personal computer known in the art, and the human-computer interaction module 6 may be a touch screen controller known in the art, and can perform human-computer interaction operation based on the touch screen controller to display the Raman spectrum and nitrate nitrogen detection results of the soil sample, and at the same time, can combine with manual input to adjust laser energy and replace the calibration model.
Preferably, as shown in fig. 4, the soil sample mixing assembly 1 of the present embodiment includes a container 11, the container 11 is configured with a stirring device 12 and/or a vibrator 13, wherein a stirring end of the stirring device 12 extends into the container 11, and the container 11 can be placed on the vibrator 13. In this way, the process of sufficiently contacting and mixing the anion-exchange membrane 2 with the soil solution can be accelerated based on the stirring action of the stirring device 12 or the oscillation action of the oscillator 13. The container 11 shown in this embodiment may be a centrifuge tube, a flask, a custom container, or the like known in the art.
Meanwhile, as shown in fig. 5, the anion exchange membrane 2 shown in this embodiment is configured with a membrane fixing frame 7, the membrane fixing frame 7 includes a first pressing sheet and a second pressing sheet, the first pressing sheet and the second pressing sheet are provided with corresponding windows, the anion exchange membrane 2 is clamped between the first pressing sheet and the second pressing sheet, so that the surfaces of both sides of the anion exchange membrane 2 are exposed from the windows, and the area of the anion exchange membrane 2 performing ion exchange can be adjusted by controlling the area of the windows, so as to control the exchange capacity of the anion exchange membrane 2, and further control the range of the nitrate nitrogen content.
Further, as shown in fig. 4, the carrying structure 14 matched with the membrane fixing frame 7 can be arranged in the container 11 in the embodiment, the carrying structure 14 can be a guide frame or a clamping groove, when in use, the membrane fixing frame 7 clamped with the anion exchange membrane 2 can be directly and conveniently arranged on the carrying structure 14, so that when the anion exchange membrane 2 is in contact and mixed with soil solution, the anion exchange membrane 2 is prevented from being directly damaged by the stirring process of the stirring device 12 or vibration generated by the oscillator 13, and meanwhile, in the process of mixing operation, the hand of an operator can be prevented from being in contact with the anion exchange membrane 2 to cause other ion interference.
Preferably, as shown in fig. 3, the scattered light collection device 3 in the present embodiment includes: a laser generator 31, wherein the laser generator 31 is used for outputting laser with preset wavelength; the spectroscope 32, the coated surface of the spectroscope 32 is used for receiving the laser output from the laser generator 31 and reflecting the laser to the surface of the anion exchange membrane 2, and correspondingly, the scattered light scattered by the nitrate nitrogen on the anion exchange membrane 2 is also transmitted to the spectrum detection module 4 through the spectroscope 32.
Specifically, the laser generator 31 shown in this embodiment outputs a laser wavelength of 785nm and a maximum optical power of 500 mW. The coated surface of the beam splitter 32 shown in this embodiment is arranged at an inclination angle of 45 ° with respect to the horizontal plane.
In the structure shown in fig. 3, the laser generator 31 emits excitation laser light horizontally incident toward the coating surface of the beam splitter 32, the excitation laser light is reflected vertically downward and output by the coating surface of the beam splitter 32, and after being focused by the focusing lens 33, the excitation laser light is vertically incident to the surface of the anion exchange membrane 2 and is adsorbed to the NO in the soil sample on the surface of the anion exchange membrane 23 -The scattered light is focused by the focusing lens 33, transmitted by the spectroscope 32 and incident to the next-stage reflector 34, reflected by the reflector 34 at 90 degrees and filteredFiltering the light by the sheet 35 to filter 785nm excitation laser carried by the scattered light, so as to obtain Raman scattered light after filtering; then, the Raman scattering light can enter the spectrum detection module 4 through the optical fiber coupling, so as to obtain the Raman spectrum intensity at different spectrum shifts based on 785nm, and the content of nitrate nitrogen in the soil sample can be calculated and obtained through the processing module 5 shown in the above embodiment.
In summary, the advantages of the solution shown in this embodiment over the prior art are mainly reflected in: (1) the chemical reagent is avoided, and the purified water can be used as the soil sample mixture and the purified water extracted by nitrate nitrogen, so that the secondary pollution is avoided; (2) the method is simple to operate and rapid in measurement, can simply mix purified water, a soil sample and an anion exchange membrane, realizes extraction and enrichment of nitrate nitrogen in a stirring or oscillation mode, has low requirements on operators, and can finish the whole measurement process within 15 min; (3) the device can be used for on-site rapid detection, the integration level of the detection device is high, other chemical analysis accessories or chemical reagents cannot be used for extraction in the detection process, the operation is flexible, and the device can be used as portable on-site detection equipment.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A method for measuring the content of nitrate nitrogen in soil is characterized by comprising the following steps:
s1, mixing a soil sample with a preset amount with purified water in proportion to prepare a soil solution;
s2, mixing the prepared anion exchange membrane with the soil solution for a preset time, and then sequentially carrying out purified water cleaning and drying treatment on the anion exchange membrane;
and S3, performing spectrum detection on the nitrate nitrogen enriched on the dried anion exchange membrane, and acquiring the content of the nitrate nitrogen in the soil sample based on characteristic spectrum intensity information obtained by the spectrum detection.
2. The method for measuring soil nitrate nitrogen content according to claim 1, wherein the mixing of the prepared anion-exchange membrane with the soil solution in S2 further comprises: and (2) placing the anion exchange membrane in the soil solution, and adopting an oscillator or a stirrer to assist the anion exchange membrane to be in full contact and mixed with the soil solution.
3. The method for measuring the content of nitrate nitrogen in soil according to claim 1, wherein the step of performing spectral detection on the nitrate nitrogen enriched on the anion exchange membrane after drying in step S3 further comprises:
s31, enabling laser with preset wavelength to be incident on the surface of the anion exchange membrane, and obtaining scattered light scattered by nitrate nitrogen on the anion exchange membrane;
s32, performing spectrum detection on the scattered light through a Raman spectrum detection module to obtain Raman spectrum intensities of the scattered light at different spectrum shifts;
and S33, preprocessing the Raman spectrum intensities at different spectrum displacement positions to obtain the spectrum intensity of the nitrate nitrogen at the Raman spectrum characteristic position.
4. The method for measuring the content of nitrate nitrogen in soil according to claim 3, wherein the step of obtaining the content of nitrate nitrogen in the soil sample based on the characteristic spectral intensity information obtained by the spectral detection in S3 further comprises: combining the characteristic spectrum intensity information with a pre-established calibration model to obtain the content of nitrate nitrogen in the soil sample;
the calibration model is a calibration curve which is established in advance based on a standard soil sample corresponding to the soil sample and represents the correlation between the nitrate nitrogen content of the standard soil sample and the spectral intensity of nitrate nitrogen at the Raman spectral characteristic position.
5. The soil nitrate nitrogen content measurement method according to claim 1, wherein S1 further includes an operation of obtaining the soil sample:
digging in-situ soil at a preset depth of a preset position, removing large particles and weeds in the in-situ soil, drying the in-situ soil, and taking the dried in-situ soil as the soil sample.
6. Method for measuring the content of nitrate nitrogen in soil according to any one of claims 1 to 5, wherein the exchange groups of the anion exchange membrane comprise OH-Or Cl-。
7. A measuring apparatus for a soil nitrate nitrogen content measuring method according to any one of claims 1 to 6, comprising:
the soil sample mixing assembly is used for containing a soil solution prepared from a soil sample;
the anion exchange membrane is used for carrying out ion exchange with nitrate nitrogen in the soil solution;
the scattered light collection device is used for carrying out laser excitation on the nitrate nitrogen enriched on the anion exchange membrane so as to output scattered light;
the spectrum detection module is used for acquiring characteristic spectrum intensity information of the scattered light;
and the processing module is used for calculating the content of the nitrate nitrogen in the soil sample based on the characteristic spectrum intensity information.
8. The measurement device of claim 7, wherein the soil sample mixing assembly comprises a container configured with a stirring device or a shaker, wherein a stirring end of the stirring device extends into the container and the shaker is configured to receive the container thereon.
9. The measuring device according to claim 7, wherein the anion exchange membrane is provided with a membrane holder, the membrane holder comprises a first pressing plate and a second pressing plate, the first pressing plate and the second pressing plate are provided with corresponding windows, and the anion exchange membrane is clamped between the first pressing plate and the second pressing plate.
10. The measurement device of claim 7, wherein the scattered light collection device comprises:
the laser generator is used for outputting laser with a preset wavelength;
the coating surface of the spectroscope is used for receiving the laser output by the laser generator and reflecting the laser to the surface of the anion exchange membrane, and correspondingly, the scattered light scattered by the nitrate nitrogen on the anion exchange membrane is also transmitted to the spectrum detection module through the spectroscope.
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