CN111239275A - Method for measuring total phosphorus content of soil or sludge - Google Patents
Method for measuring total phosphorus content of soil or sludge Download PDFInfo
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- CN111239275A CN111239275A CN202010075584.4A CN202010075584A CN111239275A CN 111239275 A CN111239275 A CN 111239275A CN 202010075584 A CN202010075584 A CN 202010075584A CN 111239275 A CN111239275 A CN 111239275A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/04—Preparation or injection of sample to be analysed
- G01N30/06—Preparation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/86—Signal analysis
- G01N30/8675—Evaluation, i.e. decoding of the signal into analytical information
- G01N30/8679—Target compound analysis, i.e. whereby a limited number of peaks is analysed
Abstract
The invention relates to the technical field of environmental monitoring analysis, and discloses a method for measuring total phosphorus in soil or sludge, which comprises the following steps: (1) sample pretreatment; (2) conversion of phosphate; (3) establishing a standard curve; (4) detecting the sample by adopting a headspace gas chromatography; (5) and (6) calculating a result. The invention utilizes the phase inversion headspace gas chromatography analysis technology, firstly, phosphate reacts with calcium oxalate solid under the alkaline condition to generate calcium phosphate and release soluble oxalate, and then the oxalate can react with permanganate root under the acidic condition to generate carbon dioxide gas; the content of total phosphorus in soil and sludge samples can be calculated by measuring the chromatographic signal value of carbon dioxide generated after the phosphate is converted twice. Not only can simplify the operation flow and greatly reduce the influence of interfering substances, but also does not use an organic extractant, thereby avoiding secondary pollution and meeting the aim of green chemistry. The method of the invention is particularly suitable for the analysis of large batches of samples by soil and sludge related research units.
Description
Technical Field
The invention relates to the technical field of environmental monitoring analysis, in particular to a method for measuring the total phosphorus content of soil or sludge.
Background
Total Phosphorus (TP) is a fundamental physicochemical indicator of soil and sludge reflecting its potential for utilization, e.g., poor soils are generally low in total phosphorus content. On the other hand, if the total phosphorus content in the soil and sludge is too high, it may cause environmental hazards, such as rain wash, which can carry excess phosphorus into the water body causing eutrophication problems. Therefore, the method for effectively measuring the total phosphorus content in the soil and the sludge has important significance for the research of soil improvement and sludge resource utilization.
Since the total phosphorus in soil and sludge samples includes both inorganic and organic phosphorus, all forms of phosphorus must be converted to soluble phosphate salts by digestion processes for detection. For total phosphorus analysis of digested samples, molybdenum blue colorimetry (forming a phosphomolybdenum blue complex with phosphate having the maximum absorbance at 700 nm) based on ammonium molybdate (developer) is the most widely used method. Although this method allows accurate analysis of phosphate in water samples, there is a great error in the detection of soil and sludge samples because some co-existing interfering substances, such as silicon, arsenic and vanadium, may also react with molybdate to form blue complexes. In order to minimize the influence of these interfering substances on the spectral measurement, it is necessary to accurately adjust the pH of the sample solution to 4.4 to reduce the generation of the blue complex and reduce the interference. However, the above treatment does not completely eliminate the interfering effect of silicon due to the excessively high silicon content in the soil. In addition, some organic cations (such as cationic dyes and quaternary ammonium ions) in the sample also interfere with the phosphomolybdenum blue assay.
In order to eliminate interference from other substances in the sample matrix, researchers have proposed separation detection techniques such as Ion Chromatography (IC) and High Performance Liquid Chromatography (HPLC). Although these methods have high sensitivity for phosphate detection, there is a high possibility that the column part is damaged at the time of IC or HPLC inspection due to the presence of a large amount of fine particles, organic acids and inorganic salt crystals in the soil and sludge digestion solution. Therefore, prior to IC or HPLC detection, time-consuming and tedious pretreatment procedures such as solvent extraction, multi-step filtration, etc. must be employed to remove these substances. However, the extractant used is usually a toxic organic solvent, such as chloroform, which is harmful to the environment and to the operators. Therefore, these methods have limitations in practical applications. Therefore, the development of a rapid, simple and effective method for measuring the total phosphorus content in soil and sludge is a precondition for implementing quality supervision of environmental soil and sludge.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a method for measuring the total phosphorus content of soil or sludge.
The purpose of the invention is realized by the following technical scheme:
a method for measuring the total phosphorus content of soil or sludge comprises the following steps:
(1) sample pretreatment: putting 0.1-0.4 g of dry soil sample or dry sludge sample and 5-15 mL of concentrated nitric acid into a digestion container, and heating for 5-20 min at the temperature of 150-200 ℃;
(2) conversion of phosphate: diluting the solution obtained in the step (1) with deionized water, then placing 1-10 mL of the solution into a centrifuge tube, and adding 5-10 mL of sodium hydroxide solution, 0.5-1.0 g of calcium oxalate powder and deionized water; placing the centrifuge tube in a constant-temperature water bath shaking table at 20-60 ℃ for intensive stirring for 5-30 min, and filtering the supernatant of the solution;
putting 0.1-2 mL of the filtrate and 1.0-5.0 mL of sulfuric acid solution into a headspace sample bottle, adding 0.1-1 mL of potassium permanganate solution into another small test tube in the headspace sample bottle, and fully mixing the two solutions in the headspace sample bottle after the cap is closed to ensure that the two solutions are completely reacted;
(3) establishing a standard curve: replacing the filtrate obtained in the step (2) with known phosphate standard solutions with different concentrations, placing the filtrate in a headspace bottle, sealing the cap, uniformly mixing, placing the headspace bottle containing the standard solution to be detected in a headspace sample injector, setting the operating conditions of the headspace sample injector and the operating conditions of a gas chromatograph, then carrying out headspace gas chromatography analysis and detection, and obtaining a standard curve according to the corresponding relation between the obtained chromatographic peak area signal value of the carbon dioxide and the phosphate standard solution with known concentration;
(4) sample detection: after the treatment of the step (2), placing the headspace bottle filled with the sample to be detected in a headspace sample injector, performing headspace gas chromatography analysis by adopting the same operation conditions of the headspace sample injector and the gas chromatograph as those in the step (3), and recording the carbon dioxide chromatographic peak area signal value of the sample;
(5) and (4) calculating a result: and (4) comparing the carbon dioxide chromatographic peak area signal value obtained in the step (4) with the standard curve obtained in the step (3), and calculating to obtain the total phosphorus content in the sample.
Preferably, the concentration of the concentrated nitric acid in the step (1) is 1.0-14.5 mol/L.
Preferably, during the phosphate conversion in the step (2), the concentration of the sodium hydroxide is 1.0-5.0 mol/L; the sulfuric acid solution is 1.0-5.0 mol/L; the concentration of the potassium permanganate solution is 0.05-0.5 mol/L.
The headspace sample bottle had a volume of 21.6 mL.
Preferably, the concentration of the phosphate standard solution in the step (3) is 1-1000 mg/L calculated by phosphorus.
Preferably, the headspace sampler operating conditions in step (4) are: the balance temperature is 50-100 ℃, the balance time is 1.0-5.0 min, the vibration condition is vigorous oscillation, the balance time of the air-carrying in the headspace sample bottle is 10-20 s, the air inflation time of the pipeline is 10-20 s, the balance time of the pipeline is 1-10 s, and the loop balance time is 10-20 s.
Preferably, a GS-Q type capillary chromatographic column (30m x 0.53mm, J & W Scientific) is used in the operating conditions of the gas chromatograph in the step (3) and the step (4), and the temperature of the chromatographic column is 30-150 ℃; nitrogen is used as a carrier, and the flow rate of the nitrogen is 2.0-6.0 mL/min; the temperature of the detector of the thermal conductivity detector is 150-250 ℃.
Preferably, the soil comprises sandy soil, clay, loam and the like; the sludge comprises excess sludge of a sewage treatment plant, sediment of rivers, lakes and reservoirs and the like.
The method utilizes a headspace gas chromatography (HS-GC) method to determine the concentration of carbon dioxide generated after two-step conversion of phosphate, and indirectly obtains the total phosphorus content in soil or sludge, and has the advantages of high determination speed, high accuracy of analysis results and simple operation.
First, since the solubility product constant of calcium phosphate is much lower than that of calcium oxalate, soluble phosphate can react with calcium oxalate solids in alkaline solution to form a more insoluble calcium phosphate precipitate, releasing free oxalate ions:
the free oxalate ions then react with permanganate in the strongly acidic conditions in the headspace bottle, producing carbon dioxide:
therefore, by measuring the carbon dioxide content in the headspace bottle, the phosphate content in the sample can be indirectly measured by headspace gas chromatography.
Compared with the prior art, the invention has the following technical effects:
firstly, compared with the molybdenum blue colorimetric method, the method does not need to accurately adjust the pH value of the solution to be measured in the sample pretreatment operation before the instrument test, and the operation is simplified. In addition, the headspace gas chromatography has the function of automatic sample injection detection, and can realize the detection of large batches of soil and sludge samples.
Secondly, when the method is used for measuring the total phosphorus content of soil and sludge, an extractant is not needed, and the use of a toxic extractant is avoided, so that secondary pollution is avoided, the harm to the environment and human bodies is reduced, and the aim of green chemistry is met.
In summary, the headspace gas chromatography gave a relative standard deviation of less than 2.6% of the total phosphorus content of the soil and sludge. Therefore, it can be said that the method has better reproducibility of the detection of the yield coefficient. The yield of the total phosphorus content of the soil measured by the headspace gas chromatography is 95.7-111.2%, which shows that the method has good accuracy in the quantitative analysis of the total phosphorus in the soil and the sludge. Therefore, the method has the advantages of high determination speed, high accuracy of analysis results and simple and convenient operation. The method is particularly suitable for analyzing large-batch samples in laboratories and relevant units for soil and sludge monitoring.
Drawings
FIG. 1 is a graph showing changes in signal values of oxygen and carbon dioxide in the aerobic activated sludge culture process
FIG. 2 is a graph showing the relationship between the signal value of carbon dioxide in a flask and the increase amount of MLSS during the culture of aerobic activated sludge.
Detailed Description
The following further describes the embodiments of the present invention. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto.
Example 1 testing of soil samples
(1) Sample pretreatment: soil samples from certain farmland in Guangxi Nanning area are air-dried, crushed, ground and sieved. The detection shows that the basic physicochemical properties are as follows: red soil, pH 5.15. Taking 0.25g of dry soil sample and 10mL of concentrated nitric acid, putting the dry soil sample and the 10mL of concentrated nitric acid into a polytetrafluoroethylene microwave digestion tank with the volume of 100mL, sealing a cover, performing microwave digestion, heating for 10min, and keeping the temperature at 180 ℃;
(2) conversion of phosphate: diluting the solution obtained in the step (1) with deionized water, then placing 5mL of the solution into a centrifuge tube, and adding 5.0mL of sodium hydroxide solution (2.0mol/L), 0.5g of calcium oxalate powder and 20mL of deionized water; placing the centrifugal tube in a constant-temperature water bath shaking table at 60 ℃ for reaction, and filtering the supernatant of the solution by using a filter membrane;
putting 1mL of the filtrate and 1.0mL of sulfuric acid solution (2.0mol/L) into a headspace sample bottle, wherein a small test tube is additionally arranged in the headspace bottle, 0.5mL of potassium permanganate solution (0.2mol/L) is added into the test tube, and fully mixing the two solutions in the headspace bottle after the cap is closed to ensure that the two solutions are completely reacted;
(3) establishing a standard curve: and (3) replacing the filtrate obtained in the step (2) with known phosphate standard solutions with different concentrations, placing the filtrate in a headspace bottle, sealing the cap, uniformly mixing, placing the headspace bottle containing the standard solution to be detected in a headspace sample injector, and then carrying out headspace gas chromatography analysis and detection.
The headspace injector operating conditions were: the balance temperature is 70 ℃, the balance time is 3.0min, the balance time of the gas-carrying in the headspace sample bottle is 12s, the pipeline inflation time is 12s, the pipeline balance time is 3s, and the loop balance time is 12 s;
the gas chromatograph was operated with a GS-Q type capillary column (30 m.times.0.53 mm, J & W Scientific Co.) at a column temperature of 30 ℃; nitrogen is taken as a carrier, and the flow rate of the nitrogen is 3.1 mL/min; the detector temperature of the Thermal Conductivity Detector (TCD) is 200 ℃. Obtaining a standard curve according to the corresponding relation between the obtained carbon dioxide chromatographic peak area signal value and the phosphate standard solution with known concentration;
(4) sample detection: after the treatment of the step (2), placing the headspace bottle filled with the sample to be detected in a headspace sample injector, performing headspace gas chromatography analysis by adopting the same operation conditions of the headspace sample injector and the gas chromatograph as those in the step (3), and recording the carbon dioxide chromatographic peak area signal value of the sample;
(5) and (4) calculating a result: and (4) comparing the carbon dioxide chromatographic peak area signal value obtained in the step (4) with the standard curve obtained in the step (3), and calculating to obtain the total phosphorus content in the sample.
Complete conversion condition of phosphate
Preparing a series of phosphate standard solutions (1.0mg/L) with the same concentration, then placing 5.0mL of the solutions into a centrifuge tube, and adding 5.0mL of sodium hydroxide solution (2.0mol/L), 0.5g of calcium oxalate powder and 20mL of deionized water; respectively placing the centrifuge tubes in a constant-temperature water bath shaking table at 40-70 ℃ for reacting for 5-30 min, and filtering the supernatant of the solution by using a filter membrane;
putting 1.0mL of the filtrate and 1.0mL of sulfuric acid solution (2.0mol/L) into a headspace sample bottle, wherein a small test tube is additionally arranged in the headspace bottle, 0.5mL of potassium permanganate solution (0.2mol/L) is added into the test tube, and fully mixing the two solutions in the headspace bottle after the cap is closed to ensure that the two solutions are completely reacted;
the detection method in the above embodiment is used for detection and analysis in a headspace gas chromatograph, and the detection chromatogram of the sample in FIG. 1 is obtained. According to the figure 1, the phosphate can be completely converted by water bath reaction at 60 ℃ for 15min, and the method is reasonable and feasible in practical application.
Standard curve:
preparing a group of phosphate standard solutions (0.1-1000 mg/L) with different concentrations, adding 5mL of the series of phosphate standard solutions into a 50mL centrifuge tube, respectively adding 10mL of sodium hydroxide solution (2mol/L), 0.5g of calcium oxalate powder and 40mL of deionized water, and fixing the volume to 50 mL. The centrifuge tube was placed in a 60 ℃ constant temperature water bath shaker for reaction for 15 min. The supernatant of the above solution was filtered through a 0.45 μm membrane.
0.5mL of the above filtrate and 2.0mL of sulfuric acid solution (2.0mol/L) were taken and placed in a 21.6mL volume commercial headspace sample vial having a small tube containing 0.5mL of potassium permanganate solution (0.1 mol/L). The top cap vial was sealed with a septum and shaken well for mixing.
The detection analysis in the headspace gas chromatography is carried out according to the detection method, and the relation between the total phosphorus concentration and the corresponding carbon dioxide signal of the gas chromatography in the figure 2 is obtained, and the relation is shown as the following formula:
A＝464(±181)+151211(±591)×m (n＝7,R2＝0.999) (1)
in the formula: a is the area of the peak of the GC signal peak for carbon dioxide, and m is the total phosphorus mass (mg P).
Thus, the total phosphorus concentration in the soil or sludge (mg/kg P) can be expressed as:
in the formula: omega is total phosphorus content (mg/kg P) of the soil or sludge sample, and A is the peak area of a gas chromatography signal of carbon dioxide.
Examples 2 to 6 examination of various samples
In examples 2 to 6, different samples were tested, the process conditions are shown in table 1, and the operation is the same as example 1 except that the process conditions are not shown.
TABLE 1 detection conditions for each sample of examples 2 to 6
Comparative examples 1 to 3
The process conditions for comparative examples 1 to 3 are shown in Table 2, and the same operations as in example 1 are not shown.
TABLE 2 Process conditions for comparative examples 1 to 3
Method accuracy
(1) Reproducibility test
The examples and comparative examples each were measured in 5 replicates by headspace gas chromatography. As can be seen from Table 3, the relative standard deviation of the total phosphorus content of the soil and sludge obtained by headspace gas chromatography was less than 2.6%. Therefore, the method can be considered to have better reproducibility in the detection of the total phosphorus content. However, as can be seen from the comparative example and table 4, if the operational detection parameter conditions are not within the range of the method, the method accuracy cannot be guaranteed, and the method cannot exert the detection advantages of the soil or sludge sample, specifically, the standard deviation is more than 15%.
Table 3 example repeated tests for headspace gas chromatography
Table 4 repeatability test for comparative example headspace gas chromatography
(2) Spiked recovery test
A known amount of potassium dihydrogen phosphate was added to the same soil sample and measured by headspace gas chromatography. As shown in Table 2, the normalized recovery rate of total phosphorus content in soil measured by top air chromatography is 95.7-111.2%, which shows that the method has good accuracy in the quantitative analysis of total phosphorus in soil and sludge.
TABLE 5 recovery by spiking of headspace gas chromatography
The embodiments of the present invention have been described in detail, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, and still fall within the scope of the invention.
Claims (7)
1. A method for measuring the total phosphorus content of soil or sludge is characterized by comprising the following steps:
(1) sample pretreatment: putting 0.1-0.4 g of dry soil sample or dry sludge sample and 5-15 mL of concentrated nitric acid into a digestion container, and heating for 5-20 min at the temperature of 150-200 ℃;
(2) conversion of phosphate: diluting the solution obtained in the step (1) with deionized water, then placing 1-10 mL of the solution into a centrifuge tube, and adding 5-10 mL of sodium hydroxide solution, 0.5-1.0 g of calcium oxalate powder and deionized water; placing the centrifuge tube in a constant-temperature water bath shaking table at 20-60 ℃ for intensive stirring for 5-30 min, and filtering the supernatant of the solution;
putting 0.1-2 mL of the filtrate and 1.0-5.0 mL of sulfuric acid solution into a headspace sample bottle, adding 0.1-1 mL of potassium permanganate solution into another small test tube in the headspace sample bottle, and fully mixing the two solutions in the headspace sample bottle after the cap is closed to ensure that the two solutions are completely reacted;
(3) establishing a standard curve: replacing the filtrate obtained in the step (2) with known phosphate standard solutions with different concentrations, placing the filtrate in a headspace bottle, sealing the cap, uniformly mixing, placing the headspace bottle containing the standard solution to be detected in a headspace sample injector, setting the operating conditions of the headspace sample injector and the operating conditions of a gas chromatograph, then carrying out headspace gas chromatography analysis and detection, and obtaining a standard curve according to the corresponding relation between the obtained carbon dioxide chromatographic peak area signal value and the phosphate standard solution with known concentration;
(4) sample detection: after the treatment of the step (2), placing the headspace bottle filled with the sample to be detected in a headspace sample injector, performing headspace gas chromatography analysis by adopting the same operation conditions of the headspace sample injector and the gas chromatograph as those in the step (3), and recording the carbon dioxide chromatographic peak area signal value of the sample;
(5) and (4) calculating a result: and (4) comparing the carbon dioxide chromatographic peak area signal value obtained in the step (4) with the standard curve obtained in the step (3), and calculating to obtain the total phosphorus content in the sample.
2. The method for measuring the total phosphorus content in the soil and the sludge according to claim 1, wherein the concentration of the concentrated nitric acid in the step (1) is 1.0-14.5 mol/L.
3. The method for determining the total phosphorus content in the soil and the sludge according to claim 1, wherein the concentration of the sodium hydroxide is 1.0-5.0 mol/L during the phosphate conversion in the step (2); the sulfuric acid solution is 1.0-5.0 mol/L; the concentration of the potassium permanganate solution is 0.05-0.5 mol/L.
4. The method for determining the total phosphorus content in the soil and the sludge according to claim 1, wherein the concentration of the phosphate standard solution in the step (3) is 1-1000 mg/L calculated by phosphorus.
5. The method of determining the total phosphorus content in soils and sludges according to claim 1, wherein the headspace sampler operating conditions in step (4) are: the balance temperature is 50-100 ℃, the balance time is 1.0-5.0 min, the vibration condition is vigorous oscillation, the balance time of the air-carrying in the headspace sample bottle is 10-20 s, the air inflation time of the pipeline is 10-20 s, the balance time of the pipeline is 1-10 s, and the loop balance time is 10-20 s.
6. The method for determining the total phosphorus content in soil and sludge according to claim 1, wherein the gas chromatograph operating conditions in the step (3) and the step (4) are that a GS-Q type capillary chromatographic column (30m x 0.53mm) is used, and the temperature of the chromatographic column is 30-150 ℃; the nitrogen is used as a carrier, and the flow rate of the nitrogen is 2.0-6.0 mL/min; the temperature of the detector of the thermal conductivity detector is 150-250 ℃.
7. The method of claim 1, wherein the soil comprises sandy soil, clay and loam; the sludge comprises excess sludge of a sewage treatment plant and sediment sludge of rivers, lakes and reservoirs.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112834685A (en) * | 2020-12-31 | 2021-05-25 | 中国环境监测总站 | Method for measuring total phosphorus concentration in surface water |
| CN113029981A (en) * | 2021-03-08 | 2021-06-25 | 长春工程学院 | Method for detecting sludge total phosphorus of urban sewage plant |
| CN113866339A (en) * | 2021-09-13 | 2021-12-31 | 昆明理工大学 | Method for detecting total phosphorus content in biodiesel by accelerated oxidation-ion chromatography |
| CN114113417A (en) * | 2021-12-29 | 2022-03-01 | 复旦大学 | Solid standard curve method suitable for headspace sample injection |
| CN114414722A (en) * | 2022-01-18 | 2022-04-29 | 天脊煤化工集团股份有限公司 | Method for measuring content of carbon dioxide in phosphorite |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112834685A (en) * | 2020-12-31 | 2021-05-25 | 中国环境监测总站 | Method for measuring total phosphorus concentration in surface water |
| CN113029981A (en) * | 2021-03-08 | 2021-06-25 | 长春工程学院 | Method for detecting sludge total phosphorus of urban sewage plant |
| CN113866339A (en) * | 2021-09-13 | 2021-12-31 | 昆明理工大学 | Method for detecting total phosphorus content in biodiesel by accelerated oxidation-ion chromatography |
| CN113866339B (en) * | 2021-09-13 | 2023-11-24 | 昆明理工大学 | Method for detecting total phosphorus content in biodiesel by accelerated oxidation-ion chromatography |
| CN114113417A (en) * | 2021-12-29 | 2022-03-01 | 复旦大学 | Solid standard curve method suitable for headspace sample injection |
| CN114414722A (en) * | 2022-01-18 | 2022-04-29 | 天脊煤化工集团股份有限公司 | Method for measuring content of carbon dioxide in phosphorite |
| CN114414722B (en) * | 2022-01-18 | 2023-09-29 | 天脊煤化工集团股份有限公司 | Method for measuring carbon dioxide content in phosphorite |
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