A method for efficiently extracting polycyclic aromatic hydrocarbons from sediments

Abstract

The present invention relates to the technical field of pollutant analysis and detection, and discloses a method for efficiently extracting polycyclic aromatic hydrocarbons from sediments. By adjusting the pH value of the sediment sample and separately extracting after solid-liquid separation, the extraction efficiency of polycyclic aromatic hydrocarbons can be significantly improved, and the final detected concentration is much higher than that of directly extracting the sediment sample without pH adjustment. Thereby, the understanding of the concentration range of polycyclic aromatic hydrocarbons in sediments is corrected, the accuracy of subsequent analysis and detection is improved, and a strong guarantee is provided for the detailed study of the environmental behavior, toxicological characteristics, etc. of polycyclic aromatic hydrocarbons.

Description

Technical Field

[0001] The invention relates to the technical field of water pollution control and sewage treatment, and in particular to a method for efficiently extracting polycyclic aromatic hydrocarbons from sediments. Background Art

[0002] As a key part of the urban drainage system, rainwater pipes receive pollutants from a variety of sources, including direct discharge of industrial and commercial wastewater, domestic sewage overflow, and surface runoff scouring, including a large number of polycyclic aromatic hydrocarbons (PAHs). These PAHs gradually accumulate in the sewer environment and hide in the sediments, forming a long-term source of pollution. However, PAHs are chemically stable and difficult to degrade naturally. They will persist in sediments and continuously increase the pollution load. On the other hand, the complex hydraulic conditions and biochemical environment of the sewer may cause a series of transformations of PAHs to generate more toxic or more difficult to treat derivatives.

[0003] When sewer sediments are resuspended and released into water bodies under heavy rain, PAHs will spread and affect the survival and reproduction of aquatic organisms. If the polluted water is used for agricultural irrigation or has hydraulic connection with drinking water sources, PAHs may also enter the soil and drinking water systems, posing a potential threat to terrestrial ecosystems and human health, increasing the risk of chronic diseases such as cancer and cardiovascular disease, and seriously undermining the balance and stability of the entire ecosystem and the human living environment. Therefore, PAHs pollution in sewer sediments has become a serious and urgent environmental problem.

[0004] In response to the challenge of PAHs pollution in sewer sediments, a series of targeted removal technologies have emerged. For example, strong oxidizing agents such as hydrogen peroxide and potassium permanganate can be used to react with PAHs to destroy their complex chemical structure and convert them into small molecules that are easy to handle later. Alternatively, physical separation technology can be used to separate PAHs from sediments based on the differences in physical properties between PAHs and sediment particles. However, no matter which treatment method is used, accurate quantitative analysis of PAHs in sediments is required to evaluate the removal effect. Therefore, it is particularly important to ensure the accuracy of PAHs detection in sediments.

[0005] At present, the most commonly used method in related research is: first, dry the collected sediment samples at low temperature (40℃-60℃), remove large particles of impurities and foreign matter in the samples, and then use mortars or ball mills to grind them into fine powder, sieve them to make the samples more uniform, and ensure the accuracy of subsequent extraction and analysis; then, Soxhlet extraction, pressurized fluid extraction, microwave-assisted extraction or ultrasonic-assisted extraction can be used for extraction; finally, concentrate and purify. Common concentration methods include vacuum distillation, rotary evaporation and nitrogen blowing, and purification methods include silica gel column / florisil (magnesium silicate) column chromatography, solid phase extraction, etc. Gel chromatography can also be used for purification. However, the above methods ignore that the sediment itself is a solid-liquid mixture. Simply drying or direct cold drying loses PAHs dissolved in the liquid phase, resulting in a low actual detection concentration. At the same time, since the occurrence state of PAHs is affected by many factors, the above methods are difficult to guarantee the extraction efficiency.

[0006] According to the characteristics of PAHs, pH is one of the key factors affecting the solubility of PAHs. By adjusting the pH value, it is helpful to weaken the adsorption force between PAHs and sediment particles, promote the migration of PAHs from the solid phase to the liquid phase, and thus efficiently extract PAHs from sediments. The present invention aims to provide an innovative solution to address the key technical problems that need to be solved in the current environmental field. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for efficiently extracting polycyclic aromatic hydrocarbons from sediments.

[0008] The object of the present invention is to provide a method for efficiently extracting polycyclic aromatic hydrocarbons from sediments, comprising the following steps:

[0009] (1) adjusting the pH of the polycyclic aromatic hydrocarbons-containing sediment; performing centrifugation and ultrasonication, and performing ultrasonication and centrifugation after heating to obtain a supernatant and a solid phase sediment;

[0010] (2) The solid phase sediment is freeze-dried, ground and sieved; and then mixed with the extract to obtain a mixed solution;

[0011] (3) shaking and ultrasonicating the mixed solution obtained in step (2); collecting the ultrasonic extract by centrifugation, filtering the collected extract and storing it, and repeating the extraction multiple times;

[0012] (4) concentrating the extract collected in step (3), and re-dissolving the concentrated product with an organic solvent, dichloromethane, to obtain a re-dissolved sample;

[0013] (5) adding the supernatant obtained in step (1) to the mixed solvent and shaking the mixture, then standing to separate the layers, taking the lower organic solution, repeating this step multiple times, and collecting the lower organic solution;

[0014] (6) The reconstituted sample obtained in step (4) and the organic solution obtained in step (5) are integrated and concentrated to achieve the extraction of polycyclic aromatic hydrocarbons.

[0015] In some embodiments of the present invention, in step (1), the polycyclic aromatic hydrocarbons include naphthalene (Nap), acenaphthylene (Aceny), acenaphthene (Acen), fluorene (Fluo), phenanthrene (Phen), anthracene (Anth), fluoranthene (Fla), pyrene (Pyr), benzo(a)anthracene (B(a)A), benzo(b)fluoranthene (B(b)F), benzo(k)fluoranthene (B(k)F), benzo(j)fluoranthene (B(j)F), benzo(g,hi)perylene (B(g,h,i,)P), benzo(a)pyrene (B(a)P), chrysene (Chry), indeno(1,2,3-cd)pyrene (I(cd)P), benzo(c)phenanthrene (B(c)PH), benzo(e)pyrene (B(e)P) and 3-methylcholanthracene (3-MC).

[0016] In some embodiments of the present invention, in step (1), the pH value is 2.5-11.

[0017] In some embodiments of the present invention, in step (1), when one or more of 3-methylcholanthracene, anthracene, and fluorene are extracted, the pH value is set to 2.5-5; when one or more of acenaphthene, benzo(g,hi)perylene, and naphthalene are extracted, the pH value is set to 7-9; when one or more of acenaphthene, phenanthrene, fluoranthene, pyrene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(j)fluoranthene, benzo(a)pyrene, chrysene, indeno(1,2,3-cd)pyrene, benzo(c)phenanthrene, and benzo(e)pyrene are extracted, the pH value is set to 9-11.

[0018] In some embodiments of the present invention, in step (1), the centrifugation time is 2 to 10 minutes, the rotation speed is 3000 to 8000 rpm; and the ultrasonication time is 15 to 30 minutes.

[0019] In some embodiments of the present invention, in step (1), the heating treatment temperature is 50-70° C. and the time is 20-45 minutes.

[0020] In some embodiments of the present invention, in step (2), the extract comprises one or more of acetone, dichloromethane and n-hexane; further, preferably acetone, dichloromethane and n-hexane, or n-hexane and acetone; further, the volume ratio of acetone to dichloromethane is (1:1)-(1:2).

[0021] In some embodiments of the present invention, in step (3), the solid-liquid ratio of the solid phase deposit to the extract is 1:5 g / ml (w:v, mass to volume ratio).

[0022] In some embodiments of the present invention, in step (3), the oscillation time is 20-45 min, and the rotation speed is 800-2300 rpm;

[0023] Ultrasound time is 20-45 minutes;

[0024] The centrifugation time is 5-20 minutes, and the rotation speed is 3000-8000 rpm.

[0025] In some embodiments of the present invention, in step (4), the organic solvent is selected from one or more of dichloromethane, n-hexane, cyclohexane and toluene.

[0026] In some embodiments of the present invention, in step (5), the mixed solvent includes one or more of acetone, dichloromethane and n-hexane, and further preferably, acetone and dichloromethane, dichloromethane and n-hexane, or n-hexane and acetone; the volume ratio of acetone to dichloromethane is (1:1)-(1:2).

[0027] In some embodiments of the present invention, the specific method for extracting polycyclic aromatic hydrocarbons from sediments is:

[0028] 1. Processing of Sediment Samples

[0029] Specifically, the sediment treatment process includes adjusting the pH value of the sediment and then performing solid-liquid separation.

[0030] (1) Stir the sediment sample evenly and divide it into 6 equal parts, of which 1 part is directly packaged and freeze-dried without treatment, and the other 5 parts are adjusted with hydrochloric acid and sodium hydroxide to pH = 2.5, 5.0, 7.0, 9.0 and 11.0 respectively. The hydrochloric acid is preferably concentrated hydrochloric acid, and the sodium hydroxide solution is 2 mol / L;

[0031] (2) The five samples for pH adjustment are first centrifuged for 5 minutes, preferably at 3000 rpm. After centrifugation, the samples are shaken and ultrasonicated in an ultrasonicator for 20 minutes. After ultrasonication, the samples are centrifuged again for 5 minutes at 5000 rpm. After centrifugation, the samples are shaken again and heated for a certain time, preferably at 65°C, for 30 minutes. After heating, the samples are ultrasonicated for 2 minutes. After ultrasonication, the samples are centrifuged for 5 minutes at 8000 rpm. The supernatant is separated from the solid phase sediment. The supernatant is filtered through a 0.45 μm filter membrane and stored in a refrigerator. The solid phase sediment is freeze-dried, ground, sieved and stored.

[0032] 2. Extraction of PAHs

[0033] (1) The extracting solution for extracting polycyclic aromatic hydrocarbons is preferably a 1:1 (v:v) mixture of acetone and dichloromethane. The supernatant sample is mixed with the extracting solution at a volume ratio of 1:1, and then shaken for 30 minutes at a speed of preferably 1000 rpm. The lower organic phase is filtered through a 0.45 μm filter membrane and collected. The extraction step is repeated, preferably 3 times, and all the collected extracts are concentrated, preferably by nitrogen blowing. Dichloromethane is selected for re-dissolution. The re-dissolved sample is placed in a gas phase vial for testing;

[0034] (2) For the solid phase sediment after freeze-drying and the original sample that was directly freeze-dried without treatment, after grinding, use a 1:1 (v:v) mixture of acetone and dichloromethane as the extraction solution, and extract according to the solid-liquid ratio of 1:5 (w:v). Oscillate for 30 minutes, preferably at a speed of 1000 rpm. After oscillation, ultrasonicate for preferably 30 minutes. Collect the extract by centrifugation. The centrifugation time is 5 minutes, and the speed is preferably 5000 rpm. The collected extract is filtered through a 0.45 μm filter membrane and stored. Repeat the extraction step, preferably twice. The collected extract is integrated and concentrated, preferably by nitrogen blowing. Dichloromethane is selected for re-dissolution. The re-dissolved sample is placed in a gas phase vial for testing.

[0035] 3. Detection of polycyclic aromatic hydrocarbons

[0036] High-purity helium was used as the carrier gas at a flow rate of 1.2 mL / min. By adjusting the initial temperature, holding time and heating rate of the heating program, comparing the peak elution time, chromatographic peak separation, peak height and peak area of ​​the target pollutant, the following heating program was finally obtained: the initial temperature was 60°C, held for 1 min; then increased to 300°C at a rate of 10°C / min and held for 5 min. This heating program can ensure the normal elution of the target pollutant and good peak shape. 1 μL of sample was injected in splitless mode at 280 ℃.

[0037] The above technical solution of the present invention has the following advantages compared with the prior art:

[0038] The present invention has developed a method for comprehensively extracting PAHs from complex sediment systems, which extracts both PAHs adsorbed on solid particles and PAHs dissolved in extracellular polymers in sediments. This method makes up for the limitation of traditional methods that only extract directly from the solid phase. The present invention greatly optimizes the extraction process of PAHs by precisely controlling the pH conditions of the sediment samples. This effectively improves the extraction efficiency of PAHs.

[0039] PAHs with different structures show differentiated dissolution characteristics at specific pH values. The present invention makes clever use of this law to more accurately separate the desired PAHs in complex sediment systems, reduce interference from impurities, and improve the accuracy of subsequent analysis and detection, thus providing a strong guarantee for detailed studies on the environmental behavior and toxicological properties of PAHs.

[0040] The method proposed in the present invention is applicable to various types of sediments, whether it is river, lake, ocean sediments, or soil sediments in contaminated sites. As long as it involves the extraction of polycyclic aromatic hydrocarbons, efficient extraction can be achieved by simply adjusting the pH value. This wide applicability enables the present invention to play an important role in environmental research, pollution control and other fields in different regions and different pollution scenarios, and has extremely high promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0042] Figure 1 It is a process flow chart of the present invention.

[0043] Figure 2 is the concentration of PAHs in the sediment sample without pH adjustment of the present invention.

[0044] Figure 3 is the concentration of PAHs in the sediment sample adjusted to pH=2.5 according to the present invention.

[0045] Figure 4 is the concentration of PAHs in the sediment sample adjusted to pH=5.0 according to the present invention.

[0046] Figure 5 is the concentration of PAHs in the sediment sample adjusted to pH=7.0 according to the present invention.

[0047] Figure 6 is the concentration of PAHs in the sediment sample adjusted to pH=9.0 according to the present invention.

[0048] Figure 7 is the concentration of PAHs in the sediment sample adjusted to pH=11.0 according to the present invention. DETAILED DESCRIPTION

[0049] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0050] The detection results of 17 PAHs in the original sediment samples of the present invention are as follows:

[0051] Table 1

[0052]

[0053] Comparative Example 1

[0054] This comparative example provides a method for efficiently extracting polycyclic aromatic hydrocarbons from sediments, and the specific steps are as follows:

[0055] (1) Take 100g of sediment sample, stir it thoroughly, and then divide it into centrifuge tubes. Place it in a freeze dryer and freeze dry it directly. Grind the freeze-dried sediment thoroughly, sieve it, and weigh 10g of it and divide it into two centrifuge tubes.

[0056] (2) Use a 1:1 (v:v) mixture of acetone and dichloromethane as the extraction solution and add 25 ml of the extraction solution to each centrifuge tube.

[0057] (3) Oscillate on an oscillator at 1000 rpm for 30 minutes, followed by sonication for 30 minutes.

[0058] (4) Collect the extract after ultrasonication by centrifugation at 5000 rpm for 5 minutes. The collected extract is filtered through a 0.45 μm filter membrane and stored. Repeat extraction steps (2) to (4) twice and collect the extract.

[0059] (5) All the extracts collected in step (4) are integrated and concentrated by nitrogen blowing. After the extracts are completely blown dry, they are re-dissolved with 1 ml of dichloromethane. The re-dissolved sample is placed in a gas phase vial and nitrogen blown dry again. After that, 200 μl of dichloromethane is added. After full re-dissolution, it is ready for testing.

[0060] The specific parameters of GC-MS during the determination are:

[0061] The chromatographic column is Rtx-5MS, with a length of 30.0m, a film thickness of 0.25μm, and an inner diameter of 0.25mm. The carrier gas is high-purity helium, with a flow rate of 1.2ml / min, the injection method is splitless injection, the injection volume is 1 microliter, the injection port temperature is 250°C, the ion source temperature is 280°C, and the acquisition method is SIM (Selected Ion Monitoring). Heating program: the initial temperature is 60°C, maintained for 1min; then increased to 300°C at a rate of 10°C / min, and maintained for 5min.

[0062] Test results see Figure 2 .

[0063] Example 1

[0064] This embodiment provides a method for efficiently extracting polycyclic aromatic hydrocarbons from sediments, and the specific steps are as follows:

[0065] (1) Add 100 g of sediment sample to three beakers respectively, stir thoroughly, and then add concentrated hydrochloric acid to adjust the pH to 7.0, 5.0 and 2.5 respectively;

[0066] (2) The pH-adjusted samples were divided into centrifuge tubes and centrifuged at 3000 rpm for 5 minutes. The samples were taken out and shaken, and then ultrasonicated for 20 minutes in an ultrasonicator. After ultrasonication, the samples were centrifuged again at 5000 rpm for 5 minutes. After centrifugation, the samples were shaken again, heated at 65°C for 30 minutes, ultrasonicated for 2 minutes, and centrifuged at 8000 rpm for 5 minutes.

[0067] (3) separating the supernatant from the solid phase sediment, filtering the supernatant through a 0.45 μm filter membrane and storing it in a refrigerator, and freezing and drying the solid phase sediment, grinding it, sieving it, and storing it;

[0068] (4) treating the lyophilized solid portion in the same manner as steps (2) to (5) in Comparative Example 1;

[0069] (5) For the supernatant samples collected in step (3), 10 ml of the supernatant was added to a 1:1 (v:v) mixture of acetone and dichloromethane on a shaker at 1000 rpm for 30 minutes, then at 2000 rpm for 10 minutes. After standing, the lower organic solution was removed. This step was repeated three times to collect all the organic extracts.

[0070] (6) All the extracts collected from each supernatant sample were integrated and concentrated by nitrogen blowing. After all the extracts were blown dry, they were reconstituted with 1 ml of dichloromethane. The reconstituted samples were placed in a gas phase vial and nitrogen blown dry again. After that, 100 μl of dichloromethane was added. After full reconstitution, they were prepared for testing.

[0071] The specific parameters of GC-MS during the determination are the same as those in Comparative Example 1. The experimental results are shown in Figure 3~Figure 5 .

[0072] Depend on Figure 2~Figure 5 It can be seen from the test results that after adjusting the pH to acidic or neutral, the individual and overall extraction effects of PAHs are significantly improved. The PAH test concentration has increased by dozens to hundreds of times, and the maximum extraction multiple can even be increased by more than 1,000 times, which occurs in the extraction of chrysene. <pH=5.0<pH=7.0。

[0073] Example 2

[0074] This embodiment provides a method for efficiently extracting polycyclic aromatic hydrocarbons from sediments, and the specific steps are as follows:

[0075] 100 g of sediment sample was added to each of the three beakers and stirred thoroughly. Then 2 mol / L sodium hydroxide solution was added dropwise to adjust the pH to 9.0 and 11.0 respectively. The subsequent steps were the same as (2) to (6) in Example 1. The specific parameters of GC-MS during the measurement were the same as those in Comparative Example 1. The test results are shown in Figure 6 and Figure 7 .

[0076] Depend on Figure 6 and Figure 7 It can be seen from the test results that after adjusting the pH to alkaline, the individual and overall extraction effects of polycyclic aromatic hydrocarbons are significantly improved, and the overall effect exceeds that of Example 1, and the maximum extraction multiple can be increased by more than 3000 times, which occurs in the extraction of chrysene. <pH=5.0<pH=7.0<pH=9.0<pH=11.0。

[0077] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for efficiently extracting polycyclic aromatic hydrocarbons from sediments, characterized in that: The following steps are involved: (1) The pH value of the polycyclic aromatic hydrocarbons-containing sediment is adjusted to 2.5-11; centrifugation and ultrasonication are performed, and after heating treatment, ultrasonication and centrifugation are performed to obtain a supernatant and a solid phase sediment; (2) The solid phase sediment is freeze-dried, ground and sieved; and then mixed with the extract to obtain a mixed solution; (3) shaking and ultrasonicating the mixed solution obtained in step (2); collecting the ultrasonic extract by centrifugation, filtering the collected extract and storing it, and repeating the extraction multiple times; (4) concentrating the extract collected in step (3), and re-dissolving the concentrated product with an organic solvent to obtain a re-dissolved sample; (5) adding the supernatant obtained in step (1) to the mixed solvent and shaking the mixture, then standing to separate the layers, taking the lower organic solution, repeating this step multiple times, and collecting the lower organic solution; (6) integrating and concentrating the reconstituted sample obtained in step (4) and the organic solution obtained in step (5) to extract the polycyclic aromatic hydrocarbons; In step (1), when extracting one or more of 3-methylcholanthracene, anthracene, and fluorene, the pH value is set to 2.5-5; when extracting one or more of acenaphthene, benzo(g,hi)perylene, and naphthalene, the pH value is set to 7-9; when extracting one or more of acenaphthene, phenanthrene, fluoranthene, pyrene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(j)fluoranthene, benzo(a)pyrene, chrysene, indeno(1,2,3-cd)pyrene, benzo(c)phenanthrene, and benzo(e)pyrene, the pH value is set to 9-11.

2. The method for efficiently extracting polycyclic aromatic hydrocarbons from sediments according to claim 1, characterized in that: In step (1), the polycyclic aromatic hydrocarbons include one or more of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(j)fluoranthene, benzo(g,hi)perylene, benzo(a)pyrene, chrysene, indeno(1,2,3-cd)pyrene, benzo(c)phenanthrene, benzo(e)pyrene and 3-methylcholanthracene.

3. The method for efficiently extracting polycyclic aromatic hydrocarbons from sediments according to claim 1, characterized in that: In step (1), the centrifugation time is 2-10 minutes, the rotation speed is 3000-8000 rpm; and the ultrasonication time is 15-30 minutes.

4. The method for efficiently extracting polycyclic aromatic hydrocarbons from sediments according to claim 1, characterized in that: In step (1), the heating treatment temperature is 50-70°C and the time is 20-45 minutes.

5. The method for efficiently extracting polycyclic aromatic hydrocarbons from sediments according to claim 1, characterized in that: In step (2), the extracting solution includes one or more of acetone, dichloromethane and n-hexane.

6. The method for efficiently extracting polycyclic aromatic hydrocarbons from sediments according to claim 1, characterized in that: In step (3), the solid-liquid ratio of the solid phase deposit to the extract is 1:5 g / ml.

7. The method for efficiently extracting polycyclic aromatic hydrocarbons from sediments according to claim 1, characterized in that: In step (3), the oscillation time is 20-45 min and the rotation speed is 800-2300 rpm; Ultrasound time is 20-45 minutes; The centrifugation time is 5-20 minutes, and the rotation speed is 3000-8000 rpm.

8. The method for efficiently extracting polycyclic aromatic hydrocarbons from sediments according to claim 1, characterized in that: In step (5), the mixed solvent includes one or more of acetone, dichloromethane and n-hexane.

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