Rapid extraction and detection method for phosphorus form in water

Abstract

The invention discloses a rapid extraction and detection method for phosphorus form in water, and particularly relates to the field of analytical chemistry. The method comprises the steps of preparation of a solid-phase extraction column, solid-phase extraction of water-soluble phosphorus, back extraction and purification of extract liquor. The solid-phase extraction column filler disclosed by the invention adopts the lanthanum-zirconium-aluminum-based composite adsorbent, so that the solid-phase extraction column filler is large in adsorption capacity and high in rate, and has a relatively good adsorption effect on inorganic phosphorus and organic phosphorus; an iron-manganese-based adsorbent is not used as a solid-phase extraction column filler, so that the influence of paramagnetic substances such as iron and manganese in an extraction solution on nuclear magnetic resonance is greatly reduced, and the resolution ratio is improved; compared with a method for freeze-drying a large-volume water sample, the solid-phase extraction method for determining the form of the water-soluble phosphorus has the advantages of simplicity, convenience and large-scale determination.

Description

Technical Field

[0001] The invention relates to the field of analytical chemistry, and in particular to a method for quickly extracting and detecting phosphorus forms in water. Background Art

[0002] Phosphorus is an essential macronutrient for the growth and survival of aquatic organisms. Excessive phosphorus is one of the important factors leading to eutrophication of water bodies. Water-soluble phosphorus is a key participant in the biochemical cycle of phosphorus in water bodies. Determining the form of water-soluble phosphorus is of great significance for understanding the fate of phosphorus and predicting the environmental chemical behavior of phosphorus.

[0003] Existing technologies focus more on the concentration of water-soluble phosphorus, often using the molybdenum blue colorimetric method to directly measure the inorganic phosphorus content, or using the molybdenum blue colorimetric method to measure the total phosphorus content after persulfate digestion. It is difficult to ascertain the existence form of water-soluble phosphorus in water bodies and its impact on organisms and the environment.

[0004] At present, the research cases on the forms of water-soluble phosphorus are limited by the low phosphorus content in water. The main method is to freeze-dry a large amount of water samples (50L-100L). 13 P-NMR phosphorus nuclear magnetic resonance method. This method is time-consuming and difficult to measure on large batches of samples. It also ignores the influence of paramagnetic substances such as iron and manganese compounds enriched in freeze-dried samples on nuclear magnetic resonance, which greatly limits the accuracy and reliability of the determination of water-soluble phosphorus forms in water. Summary of the invention

[0005] To this end, the present invention provides a method for rapid extraction and detection of phosphorus forms in water to solve the above-mentioned problems.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: According to the present invention, a method for rapid extraction and detection of phosphorus forms in water is provided, the method comprising: Step 1: Preparation of SPE Column Alumina hydrate, zirconium hydrate and lanthanum hydrate are mixed and loaded into a solid phase extraction column as a filler to serve as an adsorbent; Step 2: Solid Phase Extraction of Water-soluble Phosphorus The solid phase extraction column is placed in a solid phase extraction device, and the water sample to be extracted is pretreated and then extracted multiple times to obtain an enriched extraction; Step 3: Stripping The NaOH solution is pumped into the extraction column, and the column is repeatedly eluted for back extraction to obtain an extract; Step 4: Purification of the extract Add EDTA solution to the extract, let it stand and then centrifuge. Filter the supernatant, freeze-dry it, re-dissolve it in NaOH and centrifuge it again. Take the supernatant and add internal standard for liquid phase analysis. 31 P-NMR nuclear magnetic resonance determination.

[0007] Furthermore, in step 1, the ratio of hydrated aluminum oxide, hydrated zirconium oxide and hydrated lanthanum oxide is (0.5-1.5):(0.5-1.5):(0.5-1.5). As an example, preferably, the ratio of hydrated aluminum oxide, hydrated zirconium oxide and hydrated lanthanum oxide is 1:1:1. Furthermore, in step 1, the filler particle size is less than 45 μm, the filler amount is 100 mg-1500 mg, and hydrophobic sieve plates are provided above and below the filler. As an example, the preferred filler volume is 30 mm×26.4 mm.

[0008] Furthermore, in the step 2, the pretreatment is to pass the phosphorus-containing water sample through 0.45 μm.

[0009] Furthermore, in step 2, the extraction speed is 1-5 mL / min, and as an example, 2 mL / min is preferred. The extraction speed affects the adsorption effect. If the flow rate is too fast, it is not easy to be adsorbed. If the flow rate is too slow, the extraction time will be prolonged and the efficiency will be reduced. The single extraction time depends on the volume of the water sample and the flow rate. For multiple extractions, the total extraction time increases accordingly. The flow rate of the present invention can ensure the elution effect while avoiding incomplete elution due to too fast a flow rate.

[0010] Furthermore, in step three, the back extraction flow rate is 0.5-2mL / min; the back extraction temperature is controlled at 20-28°C; and the concentration of the NaOH solution is 0.5-1.0M. Preferably, 1M NaOH solution is pumped into the extraction column at a flow rate of 1ml / min, and the column is repeatedly eluted 3-6 times, and the eluent is collected; each elution is separated by 5-10 minutes to make the reaction more complete. If the concentration of the back-extraction NaOH solution is too low, the back extraction efficiency will be low, and more elution times and NaOH solution volumes will be required to fully back extract the phosphorus; if the concentration is too high, some side reactions will occur.

[0011] The back-extraction time is generally 10-20 minutes. If the time is too short, the back-extraction will be incomplete. If the time is too long, the risk of phosphorus loss will increase or other interfering factors will be introduced.

[0012] The concentration of the NaOH solution for back extraction will affect the back extraction efficiency. If the concentration is too low, phosphorus cannot be effectively replaced from the extraction phase. If the concentration is too high, too many impurities will be introduced, which will affect the subsequent analysis and cause interference.

[0013] Furthermore, in step 4, the concentration of the EDTA solution is 0.5-1M.

[0014] Furthermore, in step 4, the amount of EDTA solution added is 5-15% of the extract.

[0015] Furthermore, in step 4, the concentration of NaOH is 5-10M.

[0016] As an example, preferably, 10% 0.5M EDTA solution is added to the extract, allowed to stand for 0.5-1.5h, centrifuged at 1000×g for 30min, and the supernatant is filtered with a 0.45μm PTFE filter membrane. After freeze-drying, the solid powder is collected and redissolved with 2mL 10M NaOH, centrifuged at 1000×g for 30min, the supernatant is taken, and the volume of the supernatant is measured.

[0017] Standing process: After adding EDTA solution, it needs to be left standing for a while to allow EDTA and metal ions to fully react to form a stable complex. The standing time is generally about 10-30 minutes, which can ensure that the complex reaction is basically completed.

[0018] Centrifugation: After standing, centrifuge at a speed of 5000-10000 rpm for 20-40 minutes. Centrifugation can precipitate the formed complex at the bottom, thereby separating the supernatant (containing the purified water-soluble phosphorus) from the precipitate.

[0019] Filtration operation: Filter the supernatant after centrifugation through filter paper or filter membrane. The pore size of the filter membrane can be selected to be 0.45μm, which can further remove the remaining tiny particle impurities.

[0020] Freeze drying operation: The filtered solution is placed in a freeze dryer for freeze drying. The temperature of the freeze drying process is generally around -40°C to -50°C, and the vacuum degree can be controlled between 1-10 Pa. The purpose of freeze drying is to remove water from the solution and obtain a solid water-soluble phosphorus extract.

[0021] The reconstituted solution is centrifuged again under similar centrifugal conditions as before, with a rotation speed of 5000-10000 rpm and a centrifugal time of 20-40 minutes, in order to remove insoluble matter or impurity aggregates that may appear during the reconstitution process and obtain a purer water-soluble phosphorus solution.

[0022] Furthermore, in step 4, the internal standard is selected from methylene diphosphonic acid-P,P'-disodium salt solution.

[0023] As an example, it is preferred to add a methylene diphosphonic acid-P,P'-disodium salt solution to a concentration of 2.5 mM as an internal standard, place it in an Advance 500M nuclear magnetic spectrometer with 10 mm DDI for measurement, and accumulate the phosphorus spectrum for 8,000 measurements. After spectrum analysis, the phosphorus form is determined by chemical shift, and the phosphorus content of each form is calculated using the internal standard and each peak area.

[0024] The present invention has the following advantages: The present invention adopts lanthanum-zirconium-aluminum-based composite adsorbents as solid phase extraction column fillers. These fillers can specifically adsorb phosphorus in water, and are extracted in multiple times, with large adsorption capacity and high rate, and have good adsorption effects on both inorganic phosphorus and organic phosphorus. Compared with traditional extraction methods, this method can process a large number of water samples, and can also well extract water samples with low phosphorus concentrations, thereby improving the extraction efficiency of phosphorus, so that low-content phosphorus forms can be detected more accurately. The hydrated aluminum oxide, hydrated zirconium oxide and hydrated lanthanum oxide in the filler have the ability to selectively adsorb phosphorus. They can distinguish phosphorus from other impurities based on the chemical properties of phosphorus (such as the charge and size of phosphate ions), reducing co-extracted interfering substances. This makes the extracted phosphorus relatively pure, which is beneficial to subsequent detection and can more accurately determine the form of phosphorus.

[0025] The solid phase extraction column filler of the present invention avoids the use of iron-manganese based adsorbents, greatly reduces the influence of paramagnetic substances such as iron and manganese in the extract on nuclear magnetic resonance, and improves the resolution.

[0026] The NaOH used in the present invention can effectively desorb phosphorus adsorbed on the solid phase extraction column filler, and can ensure a high back extraction rate through repeated elution. This back extraction method is relatively simple to operate, and can well transfer phosphorus to the extraction liquid, providing sufficient phosphorus samples for subsequent purification and detection.

[0027] The addition of EDTA solution in the present invention can complex the metal ion impurities in the extract, and the operations of centrifugation, filtration, freeze-drying and re-dissolution can further remove other impurities. The impurity content of the purified extract is greatly reduced, so that the liquid phase 31 When using P-NMR nuclear magnetic resonance measurement, the interference of impurity peaks is reduced and the accuracy of phosphorus form detection is improved.

[0028] Compared with the method of freeze-drying a large volume of water samples, the present invention uses a solid phase extraction method to determine the water-soluble phosphorus forms, which has the advantages of simplicity and large-scale determination. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0030] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0031] Figure 1 The water-soluble phosphorus form of the standard solution obtained by the solid phase extraction method provided in Example 1 of the present invention 31 P-NMR spectrum; Figure 2 The water-soluble phosphorus forms of Taihu Lake water samples obtained by solid phase extraction method provided in Example 2 of the present invention 31 P-NMR spectrum; Figure 3 The water-soluble phosphorus forms of Taihu Lake water samples obtained without solid phase extraction and back extraction provided in Comparative Example 1 of the present invention are 31 P-NMR spectrum; Figure 4 The solid phase extraction column provided in Comparative Example 2 of the present invention uses an iron-manganese based adsorbent, and the water-soluble phosphorus forms of the Taihu water sample obtained by using the iron-manganese based adsorbent as the solid phase extraction column 31 P-NMR spectrum. DETAILED DESCRIPTION

[0032] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1 This embodiment provides a method for rapid extraction and detection of phosphorus forms in water: Water sample: In order to evaluate the effect of solid phase extraction and phosphorus speciation determination in the technology of the present invention, the inventors used 2-phosphono-1,2,4-tricarboxylic acid butane sodium salt (PBTCA), disodium hydrogen phosphate (OrthoP), sodium glycerophosphate (BGP), deoxyribonucleic acid sodium salt (DNA), sodium pyrophosphate (TSPP), sodium tripolyphosphate (TPP) and adenosine-5′-triphosphate disodium salt (ATP) as characteristic phosphorus compounds to represent phosphonates, orthophosphates, monophosphates, diphosphates, pyrophosphates, inorganic polyphosphates and organic polyphosphates in water-soluble phosphorus, respectively, and prepared 50L of aqueous solution. Among them, the concentration of orthophosphate was 2.50 mg PL-1 , other forms of phosphorus total 12.5mg PL -1 . This technology was used to complete the solid phase extraction, back extraction and purification of water-soluble phosphorus according to the above method. A portion of the extract was taken and the orthophosphate content was determined by the molybdenum blue colorimetric method. Another portion of the extract was taken and digested with potassium persulfate at 121°C and 0.1MPa for 30 minutes, and the total phosphorus content was determined by the molybdenum blue colorimetric method. The content of other forms of phosphorus was obtained by subtracting the orthophosphate content from the total phosphorus content.

[0034] 1. Prepare a solid phase extraction column for water-soluble phosphorus: Mix hydrated alumina, hydrated zirconium oxide and hydrated lanthanum oxide in a ratio of 1:1:1 and load them into a SPE solid phase extraction column. The particle size of the filler is less than 45 μm, the volume of the filler is 30 mm × 26.4 mm, and hydrophobic sieve plates are set above and below the filler. The volume of the SPE tube is 60 mL.

[0035] 2. Perform solid phase extraction of water-soluble phosphorus: Place the SPE cartridge into the solid phase extraction device, and add 50-100L of water sample that has passed 0.45μm into the SPE cartridge several times to complete the enrichment and extraction of various phosphorus in the water.

[0036] 3. Re-extract water-soluble phosphorus: 1 min mL -1 Pump 10 mL of 1 M NaOH solution into the extraction column at a flow rate of 100 μl, rinse it three times, and collect the eluent.

[0037] 4. Purification of the extract: Add 10% 0.5M EDTA solution to the extract, let stand for 1 hour, and g Centrifuge for 30 min, take the supernatant and filter it with a 0.45 μm PTFE filter. Collect the solid powder after freeze-drying and redissolve it with 2 mL 10 M NaOH and dilute it with 10000 × g Centrifuge for 30 min, take the supernatant, and measure the volume of the supernatant.

[0038] 5. Liquid Phase 31 P-NMR nuclear magnetic resonance determination: Take 600μL of the extract, add methylene diphosphonic acid-P,P'-disodium salt solution to a concentration of 2.5mM as an internal standard, place it in an Advance 500M nuclear magnetic spectrometer with 10mm DDI, and measure the phosphorus spectrum cumulatively for 8000 times. After spectrum analysis, determine the phosphorus form by chemical shift, and calculate the phosphorus content of each form by the internal standard and each peak area.

[0039] The recovery rate of orthophosphate by this technology is 92.4%, and the total recovery rate of other forms of phosphorus is 88.9%, which has a good extraction effect. Figure 1 As shown, the obtained 31The P-NMR spectrum has a high resolution, and the internal standard and seven forms of phosphorus can be identified. The recovery rates of each form of phosphorus are: phosphate, 90.5%, orthophosphate, 92.4%, glycerophosphate, 88.9%, pyrophosphate, 91.0%, DNA, 88.1%, tripolyphosphate 89.5%, adenosine triphosphate, 85.7%. Therefore, this technology has good reproducibility for the phosphorus forms of the standard solution.

[0040] Example 2 This embodiment provides a method for rapid extraction and detection of phosphorus forms in water: Water samples: Natural water sample evaluation.

[0041] 100L of surface water sample from Taihu Lake was collected in August 2023. After passing through a 0.45μm filter membrane, 50L of the sample was strictly subjected to the determination of water-soluble phosphorus forms using this technical procedure.

[0042] 1. Prepare a solid phase extraction column for water-soluble phosphorus: Mix hydrated alumina, hydrated zirconium oxide and hydrated lanthanum oxide in a ratio of 1:1:1 and load them into a SPE solid phase extraction column. The particle size of the filler is less than 45 μm, the volume of the filler is 30 mm × 26.4 mm, and hydrophobic sieve plates are set above and below the filler. The volume of the SPE tube is 60 mL.

[0043] 2. Perform solid phase extraction of water-soluble phosphorus: Place the SPE cartridge into the solid phase extraction device, and add 50-100L of water sample that has passed 0.45μm into the SPE cartridge several times to complete the enrichment and extraction of various phosphorus in the water.

[0044] 3. Re-extract water-soluble phosphorus: 1 min mL -1 Pump 10 mL of 1 M NaOH solution into the extraction column at a flow rate of 100 μl, rinse it three times, and collect the eluent.

[0045] 4. Purification of the extract: Add 10% 0.5M EDTA solution to the extract, let stand for 1 hour, centrifuge at 10000×g for 30 minutes, take the supernatant and filter it with a 0.45μm PTFE filter. Collect the solid powder after freeze-drying, dissolve it in 2mL 10M NaOH, centrifuge it at 10000×g for 30 minutes, take the supernatant, and measure the volume of the supernatant.

[0046] 5. Liquid Phase 31 P-NMR nuclear magnetic resonance determination: Take 600μL of the extract, add methylene diphosphonic acid-P,P'-disodium salt solution to a concentration of 2.5mM as an internal standard, place it in an Advance 500M nuclear magnetic spectrometer with 10mm DDI, and measure the phosphorus spectrum cumulatively for 8000 times. After spectrum analysis, determine the phosphorus form by chemical shift, and calculate the phosphorus content of each form by the internal standard and each peak area.

[0047] 31P-NMR spectrum Figure 2 As shown in the figure, the recovery rate of orthophosphate by solid phase extraction is 93.3%, and the total recovery rate of other forms of phosphorus is 86.7%, which has a good extraction effect. The obtained spectrum has high signal intensity and high resolution, and can accurately identify four phosphorus forms such as orthophosphate, phospholipids, DNA, and myo-inositol hexaphosphate.

[0048] Comparative Example 1 Water sample: same as Example 2.

[0049] Detection method: Without using solid phase extraction and back extraction, take another 50L and freeze it at -80℃, and place it in a freeze dryer for freeze drying. Collect the solid powder, re-dissolve it with 3mL of 10M NaOH solution by shaking for 2h, and centrifuge it at 10,000×g and 25℃ for 15min. Take 600μL of the supernatant, add methylene diphosphonic acid-P,P'-disodium salt solution to a concentration of 2.5mM as an internal standard, place it in an Advance500M nuclear magnetic spectrometer with 10mm DDI, and measure the phosphorus spectrum cumulatively for 8000 times. The phosphorus nuclear magnetic resonance test is exactly the same as in Example 2, and a detection solution is prepared.

[0050] 31 P-NMR spectrum Figure 3 As shown in the figure, the spectrum obtained by freeze-drying method has many impurities, the main phosphorus forms cannot be identified, and the internal standard phosphorus peak signal is weak. In comparison, the phosphorus NMR signal obtained by solid phase extraction method in this technology is strong, the spectrum resolution is high, and the main water-soluble phosphorus forms can be identified.

[0051] Comparative Example 2 Water sample: same as Example 2.

[0052] Method: The solid phase extraction column is selected from iron-manganese based adsorbent, and the iron-manganese based adsorbent is used as the solid phase extraction column; the rest is completely consistent with Example 2.

[0053] 31 P-NMR spectrum Figure 4 As shown in the figure, the use of iron-manganese based adsorbents seriously affected the phosphorus NMR spectrum, with more impurities, weaker signals, and the main phosphorus forms could not be identified. In comparison, the use of aluminum-zirconium-lanthanum adsorbents can greatly improve the spectrum quality, the internal standard has a better recovery rate, and the main water-soluble phosphorus forms can be identified.

[0054] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for rapid extraction and detection of phosphorus forms in water, characterized in that: The method comprises: Step 1: Preparation of SPE Column Aluminum oxide hydrate, zirconium oxide hydrate and lanthanum oxide hydrate are mixed and loaded into a solid phase extraction column as a filler to form a solid phase extraction column; Step 2: Solid Phase Extraction of Water-soluble Phosphorus The solid phase extraction column is placed in a solid phase extraction device, and the water sample to be extracted is pretreated and then extracted multiple times to obtain an enriched extraction; Step 3: Stripping The NaOH solution is pumped into the extraction column, and the column is repeatedly eluted for back extraction to obtain an extract; Step 4: Purification of the extract Add EDTA solution to the extract, let it stand and then centrifuge. Filter the supernatant, freeze-dry it, re-dissolve it in NaOH and centrifuge it again. Take the supernatant and add internal standard for liquid phase analysis. 31 P-NMR nuclear magnetic resonance determination.

2. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 1, the ratio of hydrated aluminum oxide, hydrated zirconium oxide and hydrated lanthanum oxide is (0.5-1.5):(0.5-1.5):(0.5-1.5).

3. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 1, the filler particle size is less than 45 μm, the filler amount is 100 mg-1500 mg, and hydrophobic sieve plates are provided above and below the filler.

4. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 2, the pretreatment is to pass the phosphorus-containing water sample through 0.45 μm.

5. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 2, the extraction rate is 1-5 mL / min.

6. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 3, the back extraction flow rate is 0.5-2 mL / min; the back extraction temperature is controlled at 20-28° C.; and the concentration of the NaOH solution is 0.5-1.0 M.

7. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 4, the concentration of the EDTA solution is 0.5-1M.

8. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 4, the amount of EDTA solution added is 5-15% of the extract.

9. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 4, the concentration of NaOH is 5-10M.

10. The method for rapid extraction and detection of phosphorus forms in water according to claim 1, characterized in that: In the step 4, the internal standard is selected from a solution of methylene diphosphonic acid-P,P'-disodium salt.

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