Pretreatment method for efficiently extracting trace liquid crystal monomer in water based on membrane filtration technology

Abstract

The invention discloses a pretreatment method for efficiently extracting trace liquid crystal monomers in water based on a membrane filtration technology. The method comprises the following steps: S1, counting molecular size parameters of liquid crystal monomers; s2, selecting a filtering membrane; s3, membrane filtration separation; and S4, extraction and concentration. According to the present invention, the size-dependent extraction and membrane filtration technology is adopted, such that the problems of large organic solvent consumption, low selectivity, limited extraction efficiency, high cost and long pretreatment time in the traditional water sample pretreatment method are solved, and the selective enrichment and purification of the liquid crystal monomer in the water sample are environmentally and efficiently achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of pretreatment of environmental analysis of trace organic pollutants, and relates to a pretreatment method for efficiently extracting trace liquid crystal monomers in water based on membrane filtration technology. Background Art

[0002] Trace organic pollutants, including liquid crystal monomers (LCMs), pharmaceutically active compounds (PhACs), personal care products (PPCPs), pesticides, endocrine disrupting chemicals (EDCs), etc., have obvious characteristics of persistence, accumulation, migration, and toxicity. They are much more difficult to control than traditional pollutants and pose potential ecological risks to aquatic organisms and humans. Therefore, their monitoring, control, and governance have become a hot topic in ecological and environmental work.

[0003] At present, liquid-liquid extraction (LLE) and solid phase extraction (SPE) are the most commonly used techniques for enriching target organic compounds from water samples. However, these two methods require a large amount of samples, and for compounds with strong hydrophilicity, the extraction efficiency of LLE is usually low, and the organic solvent consumption is large, which is easy to produce emulsification and cause secondary pollution problems. SPE can effectively avoid these problems, but SPE also has problems such as uneven packing of fillers, high cost of imported solid phase extraction columns, and easy clogging. In summary, the above methods have limited extraction capacity and relatively poor selectivity, especially when the polarity and other physicochemical characteristics of the target analytes vary over a wide range, they are prone to analyte loss.

[0004] Membrane extraction technology has attracted widespread attention due to its applicability to various situations, simplicity, high selectivity, high enrichment multiples and low organic solvent usage. At present, the most widely used membrane-based pre-analysis treatment of trace organic pollutants in environmental water samples is membrane extraction technology, which is characterized by a membrane phase sandwiched between the donor phase and the acceptor phase. Through chemical reactions or high distribution coefficients, the analyte is extracted from the donor solution through the membrane into the acceptor solution (organic or aqueous solution). However, membrane extraction technology is only highly selective for specific target compounds, and it is difficult to accurately separate a class of compounds with similar sizes and large differences in physical and chemical properties. Therefore, it is very necessary to develop a membrane filtration technology that only depends on the molecular size of new pollutants and does not depend on their chemical properties. Summary of the invention

[0005] The purpose of the present invention is to provide a pretreatment method for efficiently extracting trace liquid crystal monomers in water based on membrane filtration technology. The method selects membrane materials with specific pore sizes based on the molecular size of the target compound, and completes the precise separation of trace sub-nanometer or even sub-angstrom liquid crystal monomers in water during sample pretreatment.

[0006] The technical solution for achieving the purpose of the present invention is as follows:

[0007] The pretreatment method for efficiently extracting trace liquid crystal monomers in water based on membrane filtration technology comprises the following steps:

[0008] S1. Liquid crystal monomer molecular size parameter statistics: Enter the CAS number in the Pubchem database to query the molecular weight (Mw) of the target compound, and obtain the molecular three-dimensional structure image file, optimize the molecular spatial structure through Gaussian09, and obtain the wave function file, and import it into the Multiwfn program to calculate the theoretical diameter of the target compound molecule;

[0009] S2. Selection of filter membrane: select a membrane with a molecular weight cutoff (MWCO) and a pore size smaller than the molecular weight of the target compound and the theoretical diameter of the target compound molecule as the filter membrane;

[0010] S3, membrane filtration separation: under closed conditions, high-pressure nitrogen is used as the pressure source to squeeze the water sample containing liquid crystal monomers in the sample tube. The water sample passes through the filter membrane, intercepts the target compound, and passes through water and other small molecular components to achieve solute-solute high-precision size separation;

[0011] S4, extraction and concentration: After the filtration is completed, the filter membrane is placed in the extraction solvent, and ultrasound-assisted extraction is performed. The extract is rotary evaporated to obtain a concentrated target compound solution.

[0012] In S1 of the present invention, the liquid crystal monomer is a common liquid crystal monomer, which is ethyl biphenyl nitrile, propoxy biphenyl nitrile, propyl-3,4-difluorobiphenyl, pentyloxy biphenyl nitrile, hexyloxy biphenyl nitrile, 4-cyano-4'-heptyloxy biphenyl, 1-methoxy-4-(trans-4-propylcyclohexyl)benzene, trans-trans-4-propyl-4'-vinylbicyclohexane, 4-ethoxy-2,3-difluoro-4'-propyl biphenyl, trans-trans-4-methoxy-4'-n-propyl-1,1'-bicyclohexane, 1-ethoxy-4 -(trans-4-propylcyclohexyl)benzene, octyloxybiphenyl nitrile, trans-trans-4-[(E)-1-1-propenyl]-4'-propylbicyclohexane, 1-ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene, 4'-methyl-4-pentylbiphenyl, hexylphenyl-2',3,4,5-tetrafluorobiphenyl, propylcyclohexyl-2,6,2'-trifluoro-3-trifluoromethoxyterphenyl, ethylcyclohexylphenyl-2,3-difluorophenylethyl ether, propylcyclohexylphenyl-2,3-difluorophenylethyl ether, Amyl terphenyl nitrile, trans-4'-propyl-4-(4-trifluoromethoxyphenyl) bicyclohexane, ethylcyclohexyl-4-trifluoromethoxybiphenyl, ethylphenyl-2'-fluoro-4-propylbiphenyl, propyldicyclohexyl-3,4-difluorobiphenyl, 4-butyl-4"-ethyl-2'-fluoro-terphenyl, 4-ethyl-4'-(trans-4-propylcyclohexyl)biphenyl, propyldicyclohexyl-2,3-difluorophenyl ether, ethyldicyclohexyl-3,4-difluorobiphenyl, propyldicyclohexyl-2,3-difluorobenzene ether, butyl bicyclohexyl-2,3-difluorophenyl ether, 4-[difluoro(3,4,5-trifluorophenoxy)methyl]-3,5-difluoro-4'-propylbiphenyl, propyl bicyclohexyl-2,3-difluorophenyl ether, 4'-[2-methyl-3,4,5-trifluorophenoxy-difluoromethyl]-4-(4-propylphenyl)-3',5'-difluorobenzene, trans-trans-4'-propyl-4-p-tolylbicyclohexane and trans, trans-4-(4-tolyl)-4'-vinylbicyclohexane.

[0013] Furthermore, in S1, the theoretical diameter of the target compound molecule is 1.525nm-2.556nm.

[0014] Furthermore, in S2, the filtration membrane is a nanofiltration membrane NF90 or NF270, and more preferably a nanofiltration membrane NF90.

[0015] Furthermore, in S3, a size-dependent extraction device is used for filtering and separation, and the size-dependent extraction device includes a high-purity nitrogen cylinder and an extraction main device. The high-purity nitrogen cylinder serves as a high-pressure nitrogen source and is connected to an air inlet on the extraction main device through a pipeline. The extraction main device is provided with a vent valve for releasing residual gas, a pressure gauge for detecting the operating pressure of the device, a feed port, a sample tube for holding a water sample, a membrane pool filled with a filter membrane, and a discharge port located below the membrane pool.

[0016] Furthermore, in S4, the extraction solvent is n-hexane.

[0017] Furthermore, in S4, the number of ultrasonic-assisted extractions is more than 3 times, and the duration of each ultrasonic-assisted extraction is 10 minutes.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The pretreatment method of the present invention for efficiently extracting trace liquid crystal monomers in water based on membrane filtration technology overcomes the shortcomings of large amount of organic solvent, limited extraction efficiency and relatively poor selectivity in the pretreatment method of trace organic pollutants in traditional water samples. The present invention selects membrane materials with specific pore sizes based on the molecular size of the target compound to achieve sub-nanometer or even sub-angstrom size separation between solutes, and the enrichment multiple can reach a thousand times, and effectively reduces matrix interference, improves the sensitivity of instrumental analysis, and realizes the selective enrichment and purification of liquid crystal monomers in water samples in a green and efficient manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a pretreatment method for efficiently extracting trace amounts of liquid crystal monomers in water based on membrane filtration technology.

[0021] Figure 2 This is a schematic diagram of a size-dependent extraction (SDE) device for liquid crystal monomer molecules, wherein 1 is a high-purity nitrogen cylinder, 2 is an air inlet, 3 is a vent valve, 4 is a pressure gauge, 5 is a feed inlet, 6 is a clamp, 7 is a sample tube, 8 is a membrane pool, and 9 is a discharge port.

[0022] Figure 3 These are the peak chromatograms of 35 LCMs in the positive control and sample solutions extracted based on NF90 membrane and NF270 membrane, including a) chromatogram of positive control LCMs, b) chromatogram of LCMs in sample solutions extracted based on NF90 membrane, and c) chromatogram of LCMs in sample solutions extracted based on NF270 membrane. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific embodiments and drawings.

[0024] Example 1

[0025] S1. Liquid crystal monomer molecular size parameter statistics: Enter the CAS number in the Pubchem database to query the molecular weight (Mw) of the target compound, and obtain the molecular three-dimensional structure image file, optimize the molecular spatial structure through Gaussian09, and obtain the wave function file, and import it into the Multiwfn program to calculate the theoretical diameter of the compound molecule. The molecular weights of the 35 LCMs shown in Table 1 are 207.3-492.51, and the theoretical molecular diameters are 1.525nm-2.556nm.

[0026] Table 1 List of standard LCMs compounds and their recovery rates

[0027]

[0028]

[0029] S2. Selection of filter membrane: According to the statistical LCMs molecular weight and theoretical molecular diameter, commercially available polyamide nanofiltration membranes NF90 and NF270 were selected as filter membranes. NF-90 is formed by interfacial polymerization of m-phenylenediamine and 1,3,5-benzoyl chloride, with a MWCO of 100-150 Da and an average pore size of 0.68 nm. NF270 is formed by interfacial polymerization of piperazine and 1,3,5-benzoyl chloride, with a MWCO of 300-400 and an average pore size of 0.84 nm.

[0030] S3, membrane filtration separation: prepare positive control and water sample with LCMs concentration of 100ppb. The preparation method of positive control is: add 20μl 1ppm LCMs mixed standard solution to the injection vial with 250μl inner liner tube, then add 180μl trimethylpentane (TMP), and vortex to mix. The preparation method of water sample is: take 20μl 1ppm LCMs mixed standard solution, dissolve it in 20mL acetone, mix it, add 180mL pure water, and stir it evenly. Put the membrane into the membrane pool, add appropriate amount of pure water to the sample tube, close the device, adjust the cylinder pressure valve to the membrane test pressure of 0.76MPa (when the air pressure is adjusted to 0.2-0.3MPa, droplets begin to flow down, and as the pressure increases, the water flux increases), pure water filters through the membrane, and compacts the membrane. Filter 200mL water sample according to the same operation, the membrane intercepts the target solute, and passes water and other small molecules.

[0031] S4, extraction and concentration: After filtration, remove the membrane, use 15mL n-hexane for ultrasonic extraction for 10min, transfer the extract to a rotary evaporator, and repeat this operation 3 times. The extract is concentrated to 2-3mL by rotary evaporator, blown nearly dry with nitrogen, and then re-dissolved with 200μl trimethylpentane (TMP), transferred to a sample vial equipped with a 250μl glass insert, and wait for further instrumental analysis.

[0032] S5. Instrumental analysis: A gas chromatography-triple quadrupole mass spectrometer (GC-MS / MS) was used to quantitatively analyze the target compounds. Relevant instrument parameters: The chromatographic column model is TG-5MS (30m*0.25mm*0.25um). The injection adopts the splitless injection mode, the injection volume is 1μl, the injection port temperature is 290℃, and the carrier gas flow rate is 1.2mL / min. The starting temperature of the column oven is 40℃, which is maintained for 1min, then increased to 130℃ at a heating rate of 30℃ / min, and then increased to 250℃ at a rate of 5℃ / min, and finally increased to 300℃ at a rate of 10℃ / min, and maintained for 10min. The ion source used by the mass spectrometer is the bombardment ionization source (EI), the scanning mode is the selected reaction monitoring scan (SRM), and the temperatures of the transmission line and the ion source are 280℃ and 250℃, respectively.

[0033]

[0034] The interception recovery rates of the two nanofiltration membranes NF90 and NF270 are shown in Table 1. The average membrane interception recovery rate of NF90 is 92%, and the median recovery rate is 104%. The average membrane interception recovery rate of NF270 is 55%, and the median recovery rate is 59%. It can be seen that the NF90 membrane with a smaller MWCO and pore size distribution has a better interception effect on LCMs in water. From Table 1, it can be seen that the LCMs recovery rate of the NF90 nanofiltration membrane is between 13% and 153%. Among them, 23 of the 35 target compounds have a recovery rate of >80%, indicating that the NF-90 membrane has a good interception effect on most LCMs, verifying the feasibility of the method.

[0035] Example 2

[0036] The NF90 membrane extracted with n-hexane in Example 1 was taken out, ultrasonically extracted with 15 mL of dichloromethane for 10 min, and the extract was transferred to a rotary evaporator. The operation was repeated 3 times. The extract was concentrated to 2-3 mL by rotary evaporator and nearly dried with nitrogen, then redissolved with 200 μl of trimethylpentane (TMP), transferred to a sample injection vial equipped with a 250 μl glass inner insert, and instrumental analysis was performed. The recovery rate data are shown in Table 1. The results show that the re-extraction recovery rate of 35 LCMs is ≤6%, indicating that the residual amount of LCMs is very low after the filter membrane is extracted with n-hexane, indicating that n-hexane has a good extraction effect on LCMs.

Claims

1. A pretreatment method for efficiently extracting trace amounts of liquid crystal monomers in water based on membrane filtration technology, characterized in that: The following steps are involved: S1. Liquid crystal monomer molecular size parameter statistics: Enter the CAS number in the Pubchem database to query the molecular weight of the target compound, and obtain the molecular three-dimensional structure image file, optimize the molecular spatial structure through Gaussian09, and obtain the wave function file, and import it into the Multiwfn program to calculate the theoretical diameter of the target compound molecule; S2. Selection of filter membrane: select a membrane with a molecular weight cut-off and a pore size smaller than the molecular weight of the target compound and the theoretical diameter of the target compound molecule as the filter membrane; S3, membrane filtration separation: under closed conditions, high-pressure nitrogen is used as the pressure source to squeeze the water sample containing liquid crystal monomers in the sample tube. The water sample passes through the filter membrane, intercepts the target compound, and passes through water and other small molecular components to achieve solute-solute high-precision size separation; S4, extraction and concentration: After the filtration is completed, the filter membrane is placed in the extraction solvent, and ultrasound-assisted extraction is performed. The extract is rotary evaporated to obtain a concentrated target compound solution.

2. The pre-treatment method according to claim 1, characterized in that: The liquid crystal monomers are ethyl biphenyl nitrile, propoxy biphenyl nitrile, propyl-3,4-difluorobiphenyl, pentyloxy biphenyl nitrile, hexyloxy biphenyl nitrile, 4-cyano-4'-heptyloxy biphenyl, 1-methoxy-4-(trans-4-propylcyclohexyl)benzene, trans-trans-4-propyl-4'-vinylbicyclohexane, 4-ethoxy-2,3-difluoro-4'-propyl biphenyl, trans-trans-4-methoxy-4'-n-propyl-1,1'-bicyclohexane, 1-ethoxy-4-(trans-4-propylcyclohexyl) Benzene, octyloxybiphenyl nitrile, trans-trans-4-[(E)-1-1-propenyl]-4'-propyl bicyclohexane, 1-ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene, 4'-methyl-4-pentylbiphenyl, hexylphenyl-2',3,4,5-tetrafluorobiphenyl, propylcyclohexyl-2,6,2'-trifluoro-3-trifluoromethoxy terphenyl, ethylcyclohexylphenyl-2,3-difluorophenyl ether, propylcyclohexylphenyl-2,3-difluorophenyl ether, pentyl terphenyl nitrile, trans -4'-propyl-4-(4-trifluoromethoxyphenyl)bicyclohexane, ethylcyclohexyl-4-trifluoromethoxybiphenyl, ethylphenyl-2'-fluoro-4-propylbiphenyl, propylbicyclohexyl-3,4-difluorobiphenyl, 4-butyl-4''-ethyl-2'-fluoro-terphenyl, 4-ethyl-4'-(trans-4-propylcyclohexyl)biphenyl, propylbicyclohexyl-2,3-difluorophenyl ether, ethylbicyclohexyl-3,4-difluorobiphenyl, propylbicyclohexyl-2,3-difluoroanisole, butyl One or more of bicyclohexyl-2,3-difluorophenethyl ether, 4-[difluoro(3,4,5-trifluorophenoxy)methyl]-3,5-difluoro-4'-propylbiphenyl, propylbicyclohexyl-2,3-difluorophenethyl ether, 4'-[2-methyl-3,4,5-trifluorophenoxy-difluoromethyl]-4-(4-propylphenyl)-3',5'-difluorobenzene, trans-trans-4'-propyl-4-p-tolylbicyclohexane and trans, trans-4-(4-tolyl)-4'-vinylbicyclohexane.

3. The pre-treatment method according to claim 1, characterized in that: In S1, the theoretical diameter of the target compound molecule is 1.525nm-2.556nm.

4. The pre-treatment method according to claim 1, characterized in that: In S2, the filtration membrane is a nanofiltration membrane NF90 or NF270.

5. The pre-treatment method according to claim 1, characterized in that: In S3, a size-dependent extraction device is used for filtering and separation. The size-dependent extraction device includes a high-purity nitrogen cylinder and an extraction main device. The high-purity nitrogen cylinder serves as a high-pressure nitrogen source and is connected to an air inlet on the extraction main device through a pipeline. The extraction main device is provided with a vent valve for releasing residual gas, a pressure gauge for detecting the operating pressure of the device, a feed port, a sample tube for holding a water sample, a membrane pool filled with a filter membrane, and a discharge port located below the membrane pool.

6. The pre-treatment method according to claim 1, characterized in that: In S4, the extraction solvent is n-hexane.

7. The pre-treatment method according to claim 1, characterized in that: In S4, the number of ultrasonic-assisted extractions was more than 3 times, and the duration of each ultrasonic-assisted extraction was 10 min.

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