Method for detecting active organic carbon in soil based on fluorescence spectrometry

Abstract

The invention discloses a method for detecting soil active organic carbon based on fluorescence spectrometry, and belongs to the technical field of soil detection. The method comprises the following steps: sequentially drying, sieving and grinding fresh soil to obtain a soil sample, and sequentially performing active organic carbon extraction, purification, decoloration and pH regulation on the soil sample to obtain a soil liquid to be detected. The method comprises the following steps: adding fluorescein into a soil liquid to be detected to form a soil internal standard detection liquid, obtaining a soil fluorescence spectrum through three-dimensional fluorescence spectrum scanning, carrying out background deduction and correction coefficient correction, and calculating the active organic carbon concentration of the soil by using tryptophan, tyrosine and SMP fluorescence concentration standard curves. According to the method, an internal standard method is combined with a fluorescence spectrum technology, and through multi-step sample pretreatment and spectrum correction, the detection accuracy and the anti-interference capability are improved, the active organic carbon concentration of the soil can be rapidly and accurately determined, and an effective means is provided for soil carbon cycle research and quality evaluation.

Description

Technical Field

[0001] The present invention relates to the technical field of soil detection, and in particular to a method for detecting active organic carbon in soil based on fluorescence spectroscopy. Background Art

[0002] Soil active organic carbon (AOC) is a key active component of the soil carbon pool, and its accurate detection is crucial for soil ecological assessment and carbon cycle research. Existing detection methods, such as potassium dichromate oxidation, high-performance liquid chromatography, and carbon isotope analysis, are cumbersome, costly, and poorly resistant to interference.

[0003] Although fluorescence spectroscopy offers the potential for rapid detection, it suffers from complex soil matrix interference, imperfect pretreatment procedures, and a lack of correction mechanisms, resulting in insufficient accuracy and difficulty meeting practical application requirements. Therefore, a fluorescence spectroscopy detection method with efficient pretreatment and strong interference resistance is urgently needed. To this end, a method for detecting soil active organic carbon based on fluorescence spectroscopy is proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for detecting active organic carbon in soil based on fluorescence spectroscopy to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: A method for detecting soil active organic carbon based on fluorescence spectroscopy comprises the following steps: S1. Obtain fresh soil, dry, sieve, and grind the fresh soil in sequence to obtain a soil sample; S2. Active organic carbon was extracted from the soil sample to obtain an AOC extract, which was then purified, decolorized, and pH adjusted to obtain a soil test solution; S3. Fluorescein was added to the soil solution to be tested and mixed evenly to obtain a soil internal standard test solution with a preset fluorescein concentration. The soil internal standard test solution was tested using fluorescence spectroscopy to obtain a soil fluorescence spectrum; S4. performing background subtraction on the soil fluorescence spectrum and obtaining a correction coefficient; S5. Construct a fluorescence concentration standard curve, extract the fluorescence intensity from the soil fluorescence spectrum after background subtraction, and correct it using a correction coefficient to obtain the corrected fluorescence intensity. Substitute the corrected fluorescence intensity into the fluorescence concentration standard curve to obtain soil active organic carbon concentration data.

[0006] Preferably, the fresh soil is dried, sieved and ground in sequence: Fresh soil was collected and spread flatly in a freeze-drying bottle with a thickness not exceeding half the height of the bottle, and the soil was placed in a pre-freezing refrigerator for pre-freezing at -40°C for 2 to 4 hours. After the pre-freezing was completed, the freeze-dried bottle was transferred to a freeze dryer, the cold trap temperature was set to -50°C, the vacuum degree was maintained at 20 Pa, and the freeze-drying time was set to 24 hours, until the fresh soil was in a loose powdery state and had no moisture, thereby obtaining fresh dry soil. The fresh dry soil was taken and sieved using an 8-mesh standard soil sieve that complies with the national standard GB / T 6003.1 by a vibrating sieve method at a vibration frequency of 200 times / minute to remove impurities, thereby obtaining sieved fresh dry soil. The sieved fresh dry soil was placed in an agate mortar and ground in a circular motion, with the grinding force controlled to be uniform. The soil was passed through a 150-mesh standard sieve every 2 minutes, and the soil particles that did not pass through the 150-mesh standard sieve were repeatedly ground until they passed through the 150-mesh standard sieve, thereby obtaining a soil sample.

[0007] Preferably, the method for extracting activated carbon from soil samples is: Weigh 5 g of soil sample using an analytical balance, place it in a borosilicate glass tube, and measure 50 mL of a soil sample with a conductivity of less than 10 Deionized water was slowly added along the inner wall of the borosilicate glass tube, and the soil was gently stirred to completely immerse the soil to form a soil solution with a soil-water ratio of 1:10. The borosilicate glass tube was sealed with a polytetrafluoroethylene sealing cap, and the borosilicate glass tube was placed in a digital constant temperature water bath, and the temperature was set at 80 ° C and the oscillation speed was 80 rpm. Constant temperature oscillation was performed for 16 hours. After the oscillation was completed, the borosilicate glass tube was taken out and cooled to room temperature. The soil solution in the glass tube was transferred to a centrifuge tube, and the centrifuge tube was placed in a refrigerated centrifuge and centrifuged at a speed of 3000 rpm for 20 minutes. After the centrifugation was completed, the upper layer of the soil supernatant was aspirated using a pipette gun, and a pore size of 0.22 was selected. The supernatant liquid in the soil layer is filtered through the cellulose acetate filter membrane using a vacuum filtration device, and the filtrate after filtration is the AOC extract.

[0008] Preferably, the AOC extract is purified, decolorized and pH adjusted in sequence: A strong acid cation exchange resin was selected and placed in a beaker. 100 mL of 1 M HCl solution was added and stirred for activation for 1 hour. After activation, the strong acid cation exchange resin was repeatedly rinsed with deionized water until the pH of the filtrate was 7. The resin was transferred to another beaker, 50 mL of 1 M NaOH solution was added and stirred for 30 minutes. The resin was rinsed again with deionized water until the pH of the filtrate was 7, and the resin was drained to obtain a pretreated strong acid cation exchange resin. The AOC extract and the pretreated strong acid cation exchange resin were mixed in a 1:1 ratio and placed in a conical flask. The conical flask was shaken on a shaker with an amplitude of 20 mm for 30 minutes. After the shaking, the resin AOC mixture was transferred to a centrifuge tube. The centrifuge tube was placed in a refrigerated centrifuge and centrifuged at 2500 rpm for 10 minutes to obtain a resin AOC supernatant. The powdered activated carbon was placed in a porcelain crucible, placed in a muffle furnace, heated to 500°C at a heating rate of 5°C / min, activated at a constant temperature for 2 hours, and cooled to room temperature to obtain powdered activated carbon treated by high temperature activation. The resin AOC supernatant was pipetted into a conical flask with 0.1g of powdered activated carbon treated by high temperature activation, and the conical flask was shaken on a shaker with an amplitude of 20mm for 15 minutes. The solution in the conical flask after shaking on the shaker was filtered through a 0.45 Filter through a polyvinylidene fluoride filter membrane to obtain a decolorized AOC extract; The pH of the decolorized AOC extract was measured using a precision pH meter. Based on the pH of the decolorized AOC extract, 0.1 M dilute NaOH or 0.1 M dilute HCl solution was used to adjust the pH of the decolorized AOC extract to 7.0 to obtain a soil test solution.

[0009] Preferably, the method of using fluorescence spectroscopy to detect the soil internal standard test solution is: Set the fluorescence spectrophotometer measurement parameters, transfer 2 to 3 mL of the soil internal standard test solution to a quartz cuvette with a 1 cm optical path, and perform a three-dimensional fluorescence spectrum scan of the quartz cuvette using the fluorescence spectrophotometer to obtain the soil fluorescence spectrum; The fluorescence spectrophotometer measurement parameters include an excitation wavelength range of 220 to 450 nm, an emission wavelength range of 280 to 550 nm, a slit width of 5 nm, and a scanning speed of 1200 nm / min.

[0010] Preferably, the method for background subtraction processing of soil fluorescence spectrum is: The soil sample was spread flat on a ceramic ark, and the ceramic ark was placed in a box-type muffle furnace. The temperature was raised from room temperature to 550°C at a heating rate of 10°C / min, and constant temperature calcination was performed for 6 hours. After the high-temperature calcination was completed, the furnace temperature dropped below 100°C, the ark was taken out, and the ark was placed in a desiccator to cool to room temperature to obtain an AOC-free soil sample. 5 g of the AOC-free soil sample was weighed, and the 5 g of the AOC-free soil sample was processed in accordance with S2 and S3 steps except for adding fluorescein to the soil test solution to obtain a blank control fluorescence spectrum; Using spectrum analysis software, the blank control fluorescence spectrum was subtracted from the soil fluorescence spectrum to obtain the soil fluorescence spectrum after background subtraction. The spectrum analysis software is Origin or FLS980.

[0011] Preferably, the method for obtaining the correction coefficient is: With deionized water as solvent, based on 1.0 Fluorescent stock solution was prepared by serial dilution method with concentrations of 0.1 , 0.5 、1 , 1.5 , 2 , 3 , 4 and 5 The fluorescein standard solution is used, and the fluorescence spectrophotometer measurement parameters are set to be consistent with the fluorescence spectrophotometer measurement parameters set in the method for detecting the soil internal standard test solution using fluorescence spectroscopy; The fluorescence intensity of the corresponding fluorescein standard solution of each fluorescein concentration was measured by a fluorescence spectrophotometer with the fluorescence spectrophotometer measurement parameters set. Based on the fluorescence intensity corresponding to the fluorescein standard solution of each fluorescein concentration and the fluorescein concentration, the fluorescein concentration was used as the horizontal axis and the corresponding fluorescence intensity as the vertical axis, and the least squares method was used for linear regression to obtain the fluorescein standard curve: ; Get the preset fluorescein concentration corresponding to the soil internal standard test solution ,Will Substitute the fluorescein standard curve to obtain the expected fluorescence intensity At the same time, the measured fluorescence intensity in the soil fluorescence spectrum after background subtraction was obtained through spectrum analysis software. , based on the expected fluorescence intensity and the measured fluorescence intensity Ratio , and obtain the correction coefficient .

[0012] Preferably, the method for constructing a fluorescence concentration standard curve is: Deionized water was used as solvent and the concentration of the mixture was 0.1 , 0.5 , 1 , 5 , 10 , 15 , 25 , 35 , 45 , 55 and 70 The standard mixture solution of each standard mixture concentration is processed in accordance with steps S2 and S3 to obtain a corresponding fluorescence spectrum, and the fluorescence intensity of the tryptophan peak, the tyrosine peak, and the SMP peak in the fluorescence spectrum corresponding to the standard mixture solution of each standard mixture concentration is obtained by spectrum analysis software; Based on the fluorescence intensities of the tryptophan peak, tyrosine peak, and SMP peak corresponding to the standard mixture solutions of each standard mixture concentration and the corresponding mixture concentration, the fluorescence intensities of the tryptophan peak, tyrosine peak, and SMP peak were used as the abscissa and the corresponding mixture concentration was used as the ordinate. The least squares method was used for linear regression to obtain fluorescence concentration standard curves including a tryptophan concentration standard curve, a tyrosine concentration standard curve, and an SMP concentration standard curve, wherein the tryptophan concentration standard curve is The standard curve of tyrosine concentration is The standard curve of SMP concentration is ; The standard mixture solution is composed of tryptophan, tyrosine and glucuronolactone dissolved in deionized water in a ratio of 1:1:1; The SMP is a soluble microbial product.

[0013] Preferably, the method for obtaining soil active organic carbon concentration data is: The fluorescence intensities of the tryptophan, tyrosine, and SMP peaks in the soil fluorescence spectrum after background subtraction were obtained using spectrum analysis software, and the fluorescence intensities of the tryptophan, tyrosine, and SMP peaks were multiplied by the correction coefficients. Correction was performed to obtain the fluorescence intensity including tryptophan , tyrosine fluorescence intensity and SMP fluorescence intensity The corrected fluorescence intensity is brought into the fluorescence concentration standard curve to obtain the concentration of tryptophan. , tyrosine concentration and SMP concentration Soil labile organic carbon concentration data.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention optimizes the pretreatment process and multi-step purification process, adopts freeze-drying, 8-mesh sieve screening and 15-mesh grinding to ensure sample uniformity, combines constant temperature oscillation extraction with a soil-water ratio of 1:10, purification with a strong acidic cation exchange resin, high-temperature activated carbon decolorization and precise adjustment of pH to 7.0, effectively removes interfering substances such as soil particulate impurities, metal ions and pigments, greatly improves extraction efficiency, and significantly enhances the ability to resist matrix interference, solving the problems of cumbersome operation and serious matrix interference of traditional methods. At the same time, the innovative use of internal standard method combined with spectral correction technology, constructs a correction system with fluorescein as the internal standard, eliminates instrument fluctuations and matrix scattering errors through background subtraction and correction coefficient correction, and cooperates with multivariate standard curves covering tryptophan, tyrosine and SMP, significantly improving detection accuracy, and the three-dimensional fluorescence spectrum scanning takes a short time. The standardized operation of the whole process greatly saves detection time and reduces costs compared with traditional technologies, providing an accurate, fast and universal detection method for soil carbon cycle research and quality assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 The figure is a flow chart of the method steps of the present invention. DETAILED DESCRIPTION

[0017] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0018] Examples, such as Figure 1 As shown, a method for detecting soil active organic carbon based on fluorescence spectroscopy includes the following steps: S001 obtain fresh soil, the fresh soil was dried, sieved and ground in sequence to obtain a soil sample; S002. Active organic carbon was extracted from soil samples to obtain an AOC extract, which was then purified, decolorized, and pH adjusted to obtain a soil solution to be tested; S003. Fluorescein was added to the soil to be tested and mixed evenly to obtain a soil internal standard test solution with a preset fluorescein concentration. The soil internal standard test solution was tested using fluorescence spectroscopy to obtain a soil fluorescence spectrum. S004. Perform background subtraction on the soil fluorescence spectrum and obtain the correction coefficient; S005. Construct a fluorescence concentration standard curve, extract the fluorescence intensity from the soil fluorescence spectrum after background subtraction, and correct it using a correction coefficient to obtain the corrected fluorescence intensity. Substitute the corrected fluorescence intensity into the fluorescence concentration standard curve to obtain soil active organic carbon concentration data.

[0019] Furthermore, the working principle of the present invention is described below by way of examples: Taking the cultivated land in the North China Plain as an example, the soil type in this area is brown soil, and wheat and corn rotation crops have been planted for a long time. The background value of soil organic carbon is 12.5g / kg, and the target is to detect its active organic carbon (AOC) concentration.

[0020] 500 g of fresh soil was collected and spread flat in a freeze-drying bottle with a thickness of 1.5 cm. The soil was pre-frozen in a -40°C pre-freezing refrigerator for 3 hours and then transferred to a freeze dryer for 24 hours to obtain loose powdered fresh dry soil. The soil was sieved using an 8-mesh standard soil sieve at a vibration frequency of 200 times / min to remove gravel and plant residues. The sieved soil was placed in an agate mortar and ground in a circular grinding manner, passing through a 150-mesh sieve every 2 minutes until all the soil passed through to obtain a uniform soil sample.

[0021] Weigh 5.00 g of soil sample into a borosilicate glass tube, add 50 mL of deionized water with a conductivity of less than 10 μS / cm to form a soil solution with a soil-water ratio of 1:10, seal with a polytetrafluoroethylene cap, and shake at 80 rpm in a constant temperature water bath at 80°C for 16 hours. The shaken solution is transferred to a centrifuge tube, centrifuged at 3000 rpm for 20 minutes, and the supernatant is vacuum filtered through a 0.22 μm cellulose acetate filter to obtain an AOC extract; the AOC extract is mixed with the pretreated strong acid cation exchange resin in a 1:1 volume ratio, shaken in a conical flask at a 20 mm amplitude shaker for 30 minutes, centrifuged at 2500 rpm for 10 minutes, and the resin AOC supernatant is taken. 0.1 g of activated carbon activated at 500°C for 2 hours is added, shaken for 15 minutes, and filtered through a 0.45 μm polyvinylidene fluoride filter membrane. The pH of the filtrate is adjusted to 7.0 using 0.1 M NaO solution to obtain the soil test solution.

[0022] To 10 mL of the test solution, 10 μL of 100 mg / L fluorescein standard solution was added, mixed evenly, and 2 mL was transferred to a 1 cm quartz cuvette. A fluorescence spectrophotometer was used for three-dimensional fluorescence scanning. The measurement parameters of the fluorescence spectrophotometer were set to an excitation wavelength of 220-450 nm, an emission wavelength of 280-550 nm, a slit width of 5 nm, and a scanning speed of 1200 nm / min to obtain the soil fluorescence spectrum.

[0023] 5.00 g of soil sample was calcined in a muffle furnace at 550°C for 6 hours. Blank control spectra were prepared according to the steps of S002 and S003 without adding fluorescein. The background was subtracted using Origin software. Fluorescent standard solutions with concentrations ranging from 0.1 to 5 mg / L were prepared. The parameters were scanned using the fluorescence spectrophotometer. The fluorescein standard curve was obtained by analysis and calculation. ( ), the fluorescein concentration is mg / L of expected fluorescence intensity in the soil test solution for , i.e. 1011.2, the measured fluorescence intensity is 998.5, calculate the correction factor It is 1011.2 / 998.5, which is 1.013.

[0024] A standard mixture solution of tryptophan, tyrosine, and glucuronolactone in a 1:1:1 ratio was prepared in a concentration series of 0.1 to 70 mg / L. After treatment according to S002 and S003, a standard curve of tryptophan concentration, a standard curve of tyrosine concentration, and a standard curve of SMP concentration were established. In the soil fluorescence spectrum after background subtraction, the fluorescence intensity of the tryptophan peak was 25.6, the fluorescence intensity of the tyrosine peak was 32.4, and the fluorescence intensity of the SMP peak was 41.8. The corrected tryptophan fluorescence intensity The fluorescence intensity of tyrosine was 25.93. The fluorescence intensity of SMP was 32.82. is 42.35, which is then substituted into the fluorescence concentration standard curve to calculate: The tryptophan concentration is ; The concentration of tyrosine is ; The SMP concentration standard curve is ; Based on this, the total soil active organic carbon concentration is 107.88 mg / L, which is converted into a soil dry weight content of total soil active organic carbon of 1078.8 mg / kg, or 1.08 g / kg. The value obtained by simultaneous detection using the potassium dichromate oxidation method is 1.04 g / kg, with a relative error of 3.3%, proving the accuracy of the method.

[0025] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them. Modifications to the technical solutions described in the aforementioned embodiments, or equivalent replacements of some of the technical features therein, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for detecting soil active organic carbon based on fluorescence spectroscopy, characterized in that: The following steps are involved: S1. Obtain fresh soil, dry, sieve, and grind the fresh soil in sequence to obtain a soil sample; S2. Active organic carbon was extracted from the soil sample to obtain an AOC extract, which was then purified, decolorized, and pH adjusted to obtain a soil test solution; S3. Fluorescein was added to the soil solution to be tested and mixed evenly to obtain a soil internal standard test solution with a preset fluorescein concentration. The soil internal standard test solution was tested using fluorescence spectroscopy to obtain a soil fluorescence spectrum; S4. performing background subtraction on the soil fluorescence spectrum and obtaining a correction coefficient; S5. Construct a fluorescence concentration standard curve, extract the fluorescence intensity from the soil fluorescence spectrum after background subtraction, and correct it using a correction coefficient to obtain the corrected fluorescence intensity. Substitute the corrected fluorescence intensity into the fluorescence concentration standard curve to obtain soil active organic carbon concentration data.

2. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 1, characterized in that: The method of drying, sieving and grinding fresh soil in sequence: Fresh soil was collected and dried by freeze-drying to obtain fresh dry soil. The fresh dry soil was sieved with an 8-mesh standard soil sieve, and the sieved fresh dry soil was ground with an agate mortar to a soil particle size of 150 mesh to obtain a soil sample.

3. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 2, characterized in that: The method for extracting activated carbon from soil samples: A soil solution was prepared in a ratio of 1:10 between the soil sample and deionized water. The soil solution was placed in a glass tube, which was sealed with a polytetrafluoroethylene sealing cap. The sealed glass tube was placed in a water bath and shaken at a constant temperature. The soil solution in the glass tube after constant temperature shaking was transferred to a centrifuge tube, and the centrifuge tube was centrifuged to obtain a soil supernatant. The soil supernatant was aspirated using a pipette and filtered through a cellulose acetate filter membrane to obtain an AOC extract.

4. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 3, characterized in that: The method of sequentially purifying, decolorizing and pH adjusting the AOC extract: The AOC extract was mixed with the pretreated strong acid cation exchange resin in a ratio of 1:1, and the mixture was placed in a conical flask for shaking to obtain a resin AOC mixed solution, and the resin AOC mixed solution was transferred to a centrifuge tube for centrifugation to obtain a resin AOC supernatant; The resin AOC supernatant was pipetted into a conical flask containing 0.1 g of high-temperature activated powdered carbon, and the conical flask was shaken. The solution in the conical flask after shaking was filtered through a polyvinylidene fluoride filter membrane to obtain a decolorized AOC extract. The decolorized AOC extract was adjusted to pH 7.0 using a dilute NaOH or HCl solution to obtain a soil test solution.

5. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 4, characterized in that: The method for detecting the soil internal standard test solution using fluorescence spectroscopy: Set the measurement parameters of the fluorescence spectrophotometer, transfer a certain volume of soil internal standard test solution to a quartz cuvette with a 1 cm optical path, and perform a three-dimensional fluorescence spectrum scan of the quartz cuvette using the fluorescence spectrophotometer to obtain the soil fluorescence spectrum; The measurement parameters of the fluorescence spectrophotometer include the excitation wavelength range, the emission wavelength range, the slit width and the scanning speed.

6. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 5, characterized in that: The method for performing background subtraction processing on the soil fluorescence spectrum: The soil sample is subjected to high-temperature calcination to obtain an AOC-free soil sample, and the AOC-free soil sample is sequentially treated according to step S2 and step S3 without adding fluorescein to the soil test solution to obtain a blank control fluorescence spectrum; Using spectrum analysis software, the blank control fluorescence spectrum was subtracted from the soil fluorescence spectrum to obtain the soil fluorescence spectrum after background subtraction; The spectrum analysis software is Origin or FLS980.

7. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 6, characterized in that: The method for obtaining the correction coefficient: Using deionized water as solvent, the concentration of fluorescein was prepared as 0.1 , 0.5 , 1 , 1.5 , 2 , 3 , 4 and 5 The fluorescein standard solution is used, and the fluorescence spectrophotometer measurement parameters are set to be consistent with the fluorescence spectrophotometer measurement parameters set in the method for detecting the soil internal standard test solution using fluorescence spectroscopy; Fluorescence intensities of the corresponding fluorescein standard solutions at various fluorescein concentrations were measured by a fluorescence spectrophotometer set with the fluorescence spectrophotometer measurement parameters. Based on the fluorescence intensities corresponding to the fluorescein standard solutions at various fluorescein concentrations and the fluorescein concentrations, a linear regression was performed using the least squares method with the fluorescein concentration as the abscissa and the corresponding fluorescence intensity as the ordinate to obtain a fluorescein standard curve; Get the preset fluorescein concentration corresponding to the soil internal standard test solution ,Will Substitute the fluorescein standard curve to obtain the expected fluorescence intensity At the same time, the measured fluorescence intensity in the soil fluorescence spectrum after background subtraction was obtained through spectrum analysis software. , based on the expected fluorescence intensity and the measured fluorescence intensity , and obtain the correction coefficient .

8. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 7, characterized in that: The method for constructing a fluorescence concentration standard curve: The fluorescence concentration standard curve includes a tryptophan concentration standard curve, a tyrosine concentration standard curve and an SMP concentration standard curve; Deionized water was used as solvent and the mixture concentration was prepared by stepwise dilution method, with the concentration of 0.1 , 0.5 , 1 , 5 , 10 , 15 , 25 , 35 , 45 , 55 and 70 The standard mixture solution of each standard mixture concentration is processed in accordance with steps S2 and S3 to obtain a corresponding fluorescence spectrum, and the fluorescence intensity of the tryptophan peak, the tyrosine peak, and the SMP peak in the fluorescence spectrum corresponding to the standard mixture solution of each standard mixture concentration is obtained by spectrum analysis software; Based on the fluorescence intensities of the tryptophan peak, tyrosine peak, and SMP peak corresponding to the standard mixture solutions of each standard mixture concentration and the corresponding mixture concentration, a fluorescence concentration standard curve was obtained by linear regression using the least squares method, with the fluorescence intensities of the tryptophan peak, tyrosine peak, and SMP peak as the abscissa and the corresponding mixture concentration as the ordinate; The standard mixture solution is composed of tryptophan, tyrosine and glucuronolactone dissolved in deionized water at a ratio of 1:1:

1.

9. The method for detecting soil active organic carbon based on fluorescence spectroscopy according to claim 8, characterized in that: The method for obtaining soil active organic carbon concentration data: The fluorescence intensities of tryptophan peaks, tyrosine peaks and SMP peaks in the soil fluorescence spectrum after background subtraction were obtained using spectral analysis software. The fluorescence intensities of the tryptophan peaks, tyrosine peaks and SMP peaks were multiplied by the correction coefficients for correction to obtain the corrected fluorescence intensities including tryptophan fluorescence intensity, tyrosine fluorescence intensity and SMP fluorescence intensity. The corrected fluorescence intensities were substituted into the fluorescence concentration standard curve to obtain the soil active organic carbon concentration data including tryptophan concentration, tyrosine concentration and SMP concentration.

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