A rapid extraction and detection method for phosphorus forms in water

Abstract

The present invention discloses a method for rapid extraction and detection of phosphorus forms in water, which specifically relates to the field of analytical chemistry. The method includes the preparation of a solid-phase extraction column, solid-phase extraction of water-soluble phosphorus, back-extraction, and purification of the extraction solution. The packing material of the solid-phase extraction column in the present invention uses a lanthanum-zirconium-aluminum-based composite adsorbent, which has a large adsorption capacity, high rate, and good adsorption effects on both inorganic phosphorus and organic phosphorus; the packing material of the solid-phase extraction column avoids using an iron-manganese-based adsorbent, greatly reducing the influence of paramagnetic substances such as iron and manganese in the extraction solution on nuclear magnetic resonance and improving the resolution; compared with the method of freeze-drying large-volume water samples, the application of the solid-phase extraction method to determine the forms of water-soluble phosphorus has the advantages of simplicity and large-scale determination.

Description

Technical Field

[0001] The present invention relates to the field of analytical chemistry, and particularly relates to a method for rapid extraction and detection of phosphorus forms in water. Background Art

[0002] Phosphorus is an essential macronutrient for the growth and survival of aquatic organisms, and excessive phosphorus is one of the important factors leading to water eutrophication. Dissolved phosphorus is a key participant in the biogeochemical cycle of phosphorus in water bodies. Determining the forms of dissolved phosphorus is of great significance for understanding the fate of phosphorus and predicting the environmental chemical behavior of phosphorus.

[0003] Existing technologies mostly focus on the concentration of dissolved phosphorus, often directly measuring the content of inorganic phosphorus by the molybdenum blue colorimetric method, or measuring the total phosphorus content by the molybdenum blue colorimetric method after persulfate digestion. It is difficult to explore the existing forms of dissolved phosphorus in water bodies and its impact on organisms and the environment.

[0004] Currently, a small number of research cases on the forms of dissolved phosphorus are limited by the low phosphorus content in water. Mainly, a large amount (50L - 100L) of water samples are freeze-dried and measured by 13 P-NMR phosphorus nuclear magnetic resonance method. This method takes a long time, is difficult to measure a large number of samples, and ignores the influence of paramagnetic substances such as iron and manganese compounds enriched in freeze-dried samples on nuclear magnetic resonance, greatly limiting the accuracy and reliability of the determination of the forms of dissolved phosphorus in water. Summary of the Invention

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

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] According to a method for rapid extraction and detection of phosphorus forms in water provided by the present invention, the method includes:

[0008] Step 1: Preparation of a solid-phase extraction column

[0009] Mix hydrated alumina, hydrated zirconia and hydrated lanthanum oxide and load them into a solid-phase extraction column as an adsorbent;

[0010] Step 2: Solid-phase extraction of dissolved phosphorus

[0011] Load the solid-phase extraction column into a solid-phase extraction device. After pretreating the water sample to be extracted, perform extraction in multiple times to obtain an enriched extraction;

[0012] Step 3: Back-extraction

[0013] Pump NaOH solution into the extraction column and perform back-extraction by repeated rinsing to obtain an extract;

[0014] Step 4: Purification of the extract

[0015] Add an EDTA solution to the extract, let it stand and then centrifuge. After filtering and freeze-drying the supernatant, redissolve it with NaOH and centrifuge again. Take the supernatant and add an internal standard for liquid phase 31 P-NMR nuclear magnetic resonance measurement.

[0016] Furthermore, in the said Step 1, the ratio of hydrated alumina, hydrated zirconia and hydrated lanthanum oxide is (0.5 - 1.5):(0.5 - 1.5):(0.5 - 1.5). As an example, it is preferably 1:1:1 for hydrated alumina, hydrated zirconia and hydrated lanthanum oxide.

[0017] Furthermore, in the said Step 1, the particle size of the packing is less than 45 μm, the amount of the packing is 100 mg - 1500 mg, and hydrophobic sieve plates are arranged above and below the packing. As an example, the volume of the packing is preferably 30 mm × 26.4 mm.

[0018] Furthermore, in the said Step 2, the pretreatment is the phosphorus-containing water sample after passing through 0.45 μm.

[0019] Furthermore, in the said Step 2, the extraction rate is 1 - 5 mL / min. As an example, 2 mL / min is preferred. The extraction rate affects the adsorption effect. If the flow rate is too fast, it is not easily 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 will increase accordingly. The flow rate of the present invention can ensure the elution effect and avoid incomplete elution due to too fast flow rate.

[0020] Furthermore, in the said Step 3, the back-extraction flow rate is 0.5 - 2 mL / min; the back-extraction temperature is controlled at 20 - 28 °C; the concentration of the NaOH solution is 0.5 - 1.0 M. As a preference, pump a 1 M NaOH solution into the extraction column at a flow rate of 1 ml / min and wash it repeatedly 3 - 6 times, and collect the eluate; the interval between each wash is 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 washing times and amounts of the NaOH solution are required to fully back-extract phosphorus; if the concentration is too high, some side reactions will occur.

[0021] The back-extraction time is generally 10 - 20 minutes. If the time is too short, the back-extraction is incomplete. If the time is too long, the risk of phosphorus loss will increase or other interfering factors will be introduced.

[0022] The concentration of the back-extraction NaOH solution affects the back-extraction efficiency. If the concentration is too low, phosphorus cannot be effectively displaced 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.

[0023] Further, in the fourth step, the concentration of the EDTA solution is 0.5 - 1 M.

[0024] Further, in the fourth step, the addition amount of the EDTA solution is 5 - 15% of the extraction solution.

[0025] Further, in the fourth step, the concentration of the re-dissolved NaOH is 5 - 10 M.

[0026] As an example, it is preferred to add a 10% 0.5 M EDTA solution to the extraction solution, let it stand for 0.5 - 1.5 h, centrifuge at 1000×g for 30 min, take the supernatant and filter it through a 0.45 μm PTFE filter membrane. After freeze-drying, collect the solid powder and re-dissolve it with 2 mL of 10 M NaOH, and centrifuge at 1000×g for 30 min, take the supernatant, and measure the volume of the supernatant.

[0027] Standing process: After adding the EDTA solution, it is necessary to stand for a period of time to allow EDTA to fully react with metal ions to form stable complexes. The standing time is generally about 10 - 30 minutes, which can ensure that the complexation reaction is basically completed.

[0028] Centrifugation operation: Centrifuge after standing. The centrifugation speed is generally 5000 - 10000 revolutions per minute, and the centrifugation time can be 20 - 40 minutes. Through centrifugation, the formed complex can be precipitated at the bottom, so as to separate the supernatant (containing purified water-soluble phosphorus) from the precipitate.

[0029] Filtration operation: Filter the supernatant after centrifugation through filter paper or a filter membrane. The pore size of the filter membrane can be selected as 0.45 μm, which can further remove residual tiny particle impurities.

[0030] Freeze-drying operation: Put the filtered solution into a freeze-dryer for freeze-drying. The temperature during the freeze-drying process is generally about -40°C to -50°C, and the vacuum degree can be controlled between 1 - 10 Pa. The purpose of freeze-drying is to remove the water in the solution and obtain a solid water-soluble phosphorus extract.

[0031] The re-dissolved solution is centrifuged again. The centrifugation conditions are similar to those before, with a speed of 5000 - 10000 revolutions per minute and a centrifugation time of 20 - 40 minutes. The purpose is to remove insoluble substances or impurity aggregates that may appear during the re-dissolution process and obtain a purer water-soluble phosphorus solution.

[0032] Further, in the fourth step, the internal standard is selected from methylenediphosphonic acid - P,P'-disodium salt solution.

[0033] As an example, it is preferred to add a solution of methylenediphosphonic acid-P,P'-disodium salt to a concentration of 2.5 mM as an internal standard, and place it in an Advance 500M nuclear magnetic resonance instrument for measurement with a 10 mm DDI. The phosphorus spectrum is accumulated and measured 8000 times. After spectral analysis, the phosphorus species are determined by chemical shift, and the phosphorus content of each species is calculated based on the internal standard and the peak areas of each peak.

[0034] The present invention has the following advantages:

[0035] The present invention uses a lanthanum-zirconium-aluminum-based composite adsorbent as the packing material of the solid-phase extraction column. These packing materials can specifically adsorb phosphorus in water, and are extracted in multiple times, with a large adsorption capacity, high rate, and good adsorption effects on both inorganic phosphorus and organic phosphorus. Compared with traditional extraction methods, this method can process a large amount of water samples, and can also extract water samples with low-concentration phosphorus well, improving the extraction efficiency of phosphorus, so as to more accurately detect the phosphorus species with low content. The hydrated alumina, hydrated zirconia, and hydrated lanthanum oxide in the packing material have the ability to selectively adsorb phosphorus. They can distinguish phosphorus from other impurities according to the chemical properties of phosphorus (such as the charge and size of phosphate ions), reducing the interfering substances of co-extraction. This makes the extracted phosphorus relatively high in purity, which is beneficial to subsequent detection and can more accurately determine the phosphorus species.

[0036] The packing material of the solid-phase extraction column of the present invention avoids using iron-manganese-based adsorbents, greatly reducing the influence of paramagnetic substances such as iron and manganese in the extraction solution on nuclear magnetic resonance, and improving the resolution.

[0037] The NaOH used in the present invention can effectively desorb the phosphorus adsorbed on the packing material of the solid-phase extraction column, and a high back-extraction rate can be ensured through repeated rinsing. This back-extraction method is relatively simple in operation, and can well transfer phosphorus into the extraction solution, providing sufficient phosphorus samples for subsequent purification and detection.

[0038] The present invention adds an EDTA solution to complex metal ion impurities in the extraction solution, and operations such as centrifugation, filtration, freeze-drying, and re-dissolution further remove other impurities. After purification, the impurity content in the extraction solution is greatly reduced, so that when performing liquid-phase 31 P - NMR nuclear magnetic resonance measurement, the interference of impurity peaks is reduced, and the accuracy of phosphorus species detection is improved.

[0039] Compared with the method of freeze-drying large-volume water samples, the present invention has the advantages of simplicity and large-batch determination in applying the solid-phase extraction method to determine the water-soluble phosphorus species. Description of the Drawings

[0040] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary. For those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained based on the provided drawings.

[0041] The structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have technical substantive significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed by the present invention.

[0042] Figure 1 For the water-soluble phosphorus forms of the standard solution obtained by the solid-phase extraction method provided in Example 1 of the present invention 31 P-NMR spectrum;

[0043] Figure 2 For the water-soluble phosphorus forms of the Taihu Lake water sample obtained by applying the solid-phase extraction method provided in Example 2 of the present invention 31 P-NMR spectrum;

[0044] Figure 3 For the water-soluble phosphorus forms of the Taihu Lake water sample obtained without using solid-phase extraction and back-extraction provided in Comparative Example 1 of the present invention 31 P-NMR spectrum;

[0045] Figure 4 For the water-soluble phosphorus forms of the Taihu Lake water sample obtained by using an iron-manganese-based adsorbent as the solid-phase extraction column provided in Comparative Example 2 of the present invention 31 P-NMR spectrum. Specific Embodiments

[0046] The following specific embodiments illustrate the implementation manners of the present invention. Those who are familiar with this technology can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0047] Example 1

[0048] This example provides a method for rapid extraction and detection of phosphorus forms in water:

[0049] Water sample: To evaluate the solid-phase extraction and phosphorus speciation determination effects in the technology of the present invention, the inventors used sodium 2-phosphonobutane-1,2,4-tricarboxylate (PBTCA), disodium hydrogen phosphate (OrthoP), sodium glycerophosphate (BGP), sodium deoxyribonucleate (DNA), sodium pyrophosphate (TSPP), sodium tripolyphosphate (TPP), and disodium adenosine-5'-triphosphate (ATP) as characteristic phosphorus compounds to represent phosphonates, orthophosphates, phosphomonoesters, phosphodiesters, pyrophosphates, inorganic polyphosphates, and organic polyphosphates in water-soluble phosphorus respectively, and prepared a 50 L aqueous solution. Among them, the concentration of orthophosphate was 2.50 mg P L -1 , and the total amount of other forms of phosphorus was 12.5 mg P L -1 . Applying this technology, solid-phase extraction, back-extraction, and purification of water-soluble phosphorus were completed according to the above method. Taking a part of the extraction solution, the content of orthophosphate was determined by the molybdenum blue colorimetric method. Taking another part of the extraction solution, it was digested with potassium persulfate at 121 °C and 0.1 MPa for 30 min, and then 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.

[0050] 1. Preparation of solid-phase extraction column for water-soluble phosphorus: Hydrated alumina, hydrated zirconia, and hydrated lanthanum oxide were mixed evenly in a ratio of 1:1:1 as the packing and loaded into the SPE solid-phase extraction column. The particle size of the packing was less than 45 μm, the volume of the packing was 30 mm × 26.4 mm, hydrophobic sieve plates were provided above and below the packing, and the volume of the SPE tube was 60 mL.

[0051] 2. Solid-phase extraction of water-soluble phosphorus: The SPE column was installed in the solid-phase extraction device, and 50 - 100 L of water sample passing through 0.45 μm was added to the SPE column in multiple times to complete the enrichment extraction of various phosphorus in the water.

[0052] 3. Back-extraction of water-soluble phosphorus: Pump 10 mL of 1 M NaOH solution into the extraction column at a flow rate of 1 min mL -1 , and rinse it repeatedly 3 times, and collect the eluate.

[0053] 4. Purification of the extraction solution: Add 10% 0.5 M EDTA solution to the extraction solution, let it stand for 1 h, centrifuge at 10000× g for 30 min, take the supernatant and filter it through a 0.45 μm PTFE filter membrane. After freeze-drying, collect the solid powder and redissolve it with 2 mL of 10 M NaOH, and centrifuge at 10000× g for 30 min, take the supernatant, and measure the volume of the supernatant.

[0054] 5. Liquid phase 31P-NMR nuclear magnetic resonance determination: Take 600 μL of the extract, add disodium methylenediphosphonate solution to a concentration of 2.5 mM as the internal standard, place it in an Advance 500M nuclear magnetic resonance instrument and measure it with a 10 mm DDI. The phosphorus spectrum is accumulated and measured 8000 times. After spectral deconvolution, the phosphorus species are determined by chemical shift, and the phosphorus content of each species is calculated based on the internal standard and the peak areas of each peak.

[0055] The recovery rate of this technology for orthophosphate is 92.4%, and the total recovery rate of other phosphorus species is 88.9%, showing a good extraction effect. The results are as Figure 1 shown, and the obtained 31 P-NMR spectrum has a high resolution. The internal standard and 7 phosphorus species can all be identified. The recovery rates of each phosphorus species are as follows: phosphate, 90.5%, orthophosphate, 92.4%, glycerol phosphate, 88.9%, pyrophosphate, 91.0%, DNA, 88.1%, tripolyphosphate 89.5%, adenosine triphosphate, 85.7%. Therefore, this technology has good reproducibility for the phosphorus species in the standard solution.

[0056] Example 2

[0057] This example provides a method for rapid extraction and detection of phosphorus species in water:

[0058] Water sample: Evaluation of natural water samples.

[0059] Collect 100 L of surface water samples from Taihu Lake in August 2023. After passing through a 0.45 μm filter membrane, 50 L of it is strictly measured for water-soluble phosphorus species using the steps of this technology.

[0060] 1. Prepare a solid-phase extraction column for water-soluble phosphorus: Mix hydrated alumina, hydrated zirconia, and hydrated lanthanum oxide in a ratio of 1:1:1 as the packing and load it into an SPE solid-phase extraction column. The particle size of the packing is less than 45 μm, the volume of the packing is 30 mm × 26.4 mm, and hydrophobic sieve plates are provided above and below the packing. The volume of the SPE tube is 60 mL.

[0061] 2. Perform solid-phase extraction of water-soluble phosphorus: Install the SPE column into the solid-phase extraction device, and add 50 - 100 L of the water sample passing through 0.45 μm to the SPE column in multiple batches to complete the enrichment and extraction of various phosphorus in the water.

[0062] 3. Perform back-extraction of water-soluble phosphorus: Pump 10 mL of 1 M NaOH solution into the extraction column at a flow rate of 1 min mL -1 and rinse it repeatedly 3 times, and collect the eluate.

[0063] 4. Purification of the extract: Add 10% 0.5M EDTA solution to the extract, let it stand for 1 h, centrifuge at 10000×g for 30 min, take the supernatant and filter it through a 0.45-μm PTFE membrane. After freeze-drying, collect the solid powder, redissolve it with 2 mL 10M NaOH, centrifuge at 10000×g for 30 min, take the supernatant, and measure the volume of the supernatant.

[0064] 5. Liquid phase 31 P-NMR nuclear magnetic resonance determination: Take 600 μL of the extract, add disodium methylenediphosphonate solution to a concentration of 2.5 mM as an internal standard, place it in an Advance 500M nuclear magnetic resonance instrument and measure it with a 10-mm DDI, and accumulate the phosphorus spectrum 8000 times. After spectral analysis, determine the phosphorus species by chemical shift, and calculate the content of each phosphorus species based on the internal standard and the peak areas of each peak.

[0065] 31 The P-NMR spectrum is as Figure 2 shown. The recovery rate of orthophosphate by solid-phase extraction is 93.3%, and the total recovery rate of other phosphorus species is 86.7%, showing a good extraction effect. The obtained spectrum has high signal intensity and high resolution, and can accurately identify four phosphorus species, namely orthophosphate, phospholipid, DNA, and myo-inositol hexaphosphate.

[0066] Comparative Example 1

[0067] Water sample: The same as in Example 2.

[0068] Detection method: Without using solid-phase extraction and back-extraction, take another 50 L and freeze it at -80 °C, then place it in a freeze dryer for freeze-drying. Collect the solid powder, oscillate and redissolve it with 3 mL 10M NaOH solution for 2 h, and centrifuge at 10,000×g at 25 °C for 15 min. Take 600 μL of the supernatant, add disodium methylenediphosphonate solution to a concentration of 2.5 mM as an internal standard, place it in an Advance 500M nuclear magnetic resonance instrument and measure it with a 10-mm DDI, and accumulate the phosphorus spectrum 8000 times. The phosphorus nuclear magnetic resonance test is exactly the same as in Example 2 to prepare the detection solution.

[0069] 31 The P-NMR spectrum is as Figure 3 shown. The spectrum obtained by the freeze-drying method has more miscellaneous peaks, and the main phosphorus species cannot be identified, and the signal of the internal standard phosphorus spectrum peak is weak. In comparison, the phosphorus nuclear magnetic resonance signal obtained by using the solid-phase extraction method in this technology is strong, the spectrum resolution is relatively high, and the main water-soluble phosphorus species can be identified.

[0070] Comparative Example 2

[0071] Water sample: The same as in Example 2.

[0072] Method: An iron-manganese-based adsorbent was selected for the solid-phase extraction column, and the iron-manganese-based adsorbent was used as the solid-phase extraction column; the others were exactly the same as in Example 2.

[0073] 31 The P-NMR spectrum is as Figure 4 shown. The use of the iron-manganese-based adsorbent seriously affected the phosphorus nuclear magnetic resonance spectrum, with many impurity peaks and weak signals, and the main phosphorus forms could not be identified. In comparison, the use of the aluminum-zirconium-lanthanide series adsorbent could greatly improve the spectrum quality, the internal standard had a good recovery rate, and the main water-soluble phosphorus forms were identified.

[0074] Although the present invention has been described in detail above with general descriptions and specific examples, modifications or improvements can be made to it based on the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A rapid extraction and detection method for phosphorus forms in water, characterized in that, The method includes: Step 1: Preparation of the solid-phase extraction column Mix hydrated alumina, hydrated zirconia, and hydrated lanthanum oxide and load them into the solid-phase extraction column as the filler to form the solid-phase extraction column; the ratio of hydrated alumina, hydrated zirconia, and hydrated lanthanum oxide is (0.5 - 1.5):(0.5 - 1.5):(0.5 - 1.5); Step 2: Solid-phase extraction of water-soluble phosphorus Place the solid-phase extraction column into the solid-phase extraction device. After pretreating the water sample to be extracted, perform extraction in multiple batches to obtain the enriched extraction; the pretreatment is to pass the phosphorus-containing water sample through a 0.45-μm filter membrane; Step 3: Back-extraction Pump the NaOH solution into the extraction column and repeatedly rinse for back-extraction to obtain the extract; Step 4: Purification of the extract Add an EDTA solution to the extract, let it stand and then centrifuge. After filtration and lyophilization of the supernatant, redissolve it with NaOH and centrifuge again. Take the supernatant and add an internal standard for liquid phase 31 P-NMR nuclear magnetic resonance determination.

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

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

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

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

6. A rapid extraction and detection method for phosphorus forms in water according to claim 1, characterized in that, In Step 4, the addition amount of the EDTA solution is 5 - 15% of the extract.

7. A rapid extraction and detection method for phosphorus forms in water according to claim 1, characterized in that In Step 4, the concentration of the re-dissolved NaOH is 5 - 10 M.

8. A rapid extraction and detection method for phosphorus forms in water according to claim 1, characterized in that, In Step 4, the internal standard is selected from the solution of methylenediphosphonic acid-P,P'-disodium salt.

Images