CN102527334A - Solid phase extraction column with functionalized multi-walled carbon nanotube substrate, and preparation method thereof - Google Patents

Abstract

The invention specifically relates to a "solid-phase extraction column of a functionalized multi-walled carbon nanotube matrix and a preparation method thereof". The matrix of the solid-phase extraction column of the present invention is a functionalized multi-wall carbon nanotube, which is obtained through purification, carboxylation, acyl chloride and functionalized covalent chemical modification of the original multi-wall carbon nanotube. The packing height of the functionalized multi-walled carbon nanotube is 0.8-1.2 cm. It is mainly suitable for reverse phase extraction of non-polar to medium polar substances, and is used for enrichment and purification of target substances in the sample to be tested. The solid-phase extraction column of the present invention has the characteristics of large adsorption capacity for target substances and high recovery rate (92-103%) for target substances, low preparation cost, easy-to-obtain materials, simple functionalization process, strong adaptability, and easy mass production .

Description

Solid-phase extraction column of functionalized multi-walled carbon nanotube matrix and preparation method thereof

technical field

The invention belongs to the field of chemical analysis testing instruments and equipment. Specifically, the invention relates to a functionalized multi-walled carbon nanotube matrix solid-phase extraction column, and the invention also relates to a preparation method of the extraction column .

Background technique

Solid phase extraction (Solid phase extraction, SPE) technology has been developed in many fields since it came out in the late 1970s. In foreign countries, it has gradually replaced the traditional liquid-liquid extraction and has become a reliable and effective method for sample pretreatment. SPE technology is a separation and purification method based on the principle of liquid chromatography. The adsorbent is a stationary phase, and according to the adsorption of the solid-phase extractant to the liquid-phase analyte, when the analyte passes through the extractant, the target substance in the sample is adsorbed on the extractant. Then use a suitable selective solvent for elution or thermal desorption to achieve the purpose of separating and enriching the target compound. Compared with liquid-liquid extraction, solid-phase extraction has many advantages: solid-phase extraction does not require large amounts of mutually incompatible solvents; there is no permanent emulsification during processing. It uses an efficient and highly selective adsorbent (stationary phase), which can significantly reduce the amount of solvent used, simplify the sample processing process, and reduce the cost at the same time. Generally speaking, the time required for solid-phase extraction is 1/2 of that of liquid-liquid extraction, and the cost is 1/5 of that of liquid-liquid extraction. The disadvantage is that the recovery and precision of target compounds are lower than that of liquid-liquid extraction.

Since the Japanese scientist Sumio Iijima discovered carbon nanotubes (CNTs) in 1991, due to their unique electrical, mechanical and chemical properties, carbon nanotubes have become an emerging functional material that has attracted much attention in recent years. Carbon nanotubes have a large specific surface area and unique surface properties. The conjugated structure system of the tube wall can strongly adsorb with other compounds with conjugated structures, making it resistant to organic and inorganic pollutants in the environmental matrix. With certain adsorption and large adsorption capacity, carbon nanotubes have unique advantages as a solid phase extraction agent. It was found that the adsorption capacity of multi-walled carbon nanotubes (MWCNTs) was superior to that of C ₁₈ , silica, and activated carbon. After the adsorption and elution of carbon nanotubes, mass spectrometry, gas chromatography, high performance liquid chromatography, capillary electrophoresis, atomic absorption spectroscopy, etc. are analyzed, which simplifies the sample pretreatment process and can be successfully applied to different drugs and aromatic hydrocarbons. Detection of linear alkane compounds.

At present, the separation and enrichment of solid phase extraction using carbon nanotubes as adsorbent mainly focuses on the research of organic compounds and metal ions. Recently, some progress has been made in the use of carbon nanotubes to adsorb biological macromolecules. Carboxylated carbon nanotubes can be used to separate basic proteins, so it is possible to apply this new type of high-efficiency adsorbent to the extraction of biomacromolecules in biological samples. Biomacromolecule. In addition, carbon nanotubes also have good biocompatibility and the ability to retain the activity of adsorbed biomacromolecules, so they have broad application prospects as adsorbents for solid-phase extraction of biomacromolecules. Functionalized multi-walled carbon nanotubes can achieve specific adsorption of target substances, and its adsorption capacity is larger than that of ordinary MWCNTs SPE columns, which improves the recovery rate of target substances. Therefore, functionalized multi-walled carbon nanotubes with different functions can be prepared for different target substances. However, there are few commercialized f-MWCNTs SPE columns in the market. Most of the f-MWCNTs SPE columns are filled manually by the experimenter, and it is difficult to have a certain standard.

Carbon nanotubes are a kind of polymer inorganic material, and the adsorption force between the tubes is strong. Therefore, carbon nanotubes are insoluble in water and organic solvents and difficult to disperse in bundles, which limits the application research of carbon nanotubes in various fields. But the main reason is broad.

Contents of the invention

The object of the present invention is to provide a solid-phase extraction column of a functionalized multi-walled carbon nanotube matrix, which will be used as a new type of sample pretreatment material for reverse-phase extraction of non-polar to moderately polar substances for enrichment , Purify target substances in water samples, food or cosmetics.

Another object of the present invention is to provide a method for preparing a solid-phase extraction column of a functionalized multi-walled carbon nanotube matrix.

The object of the present invention is achieved like this: a kind of solid-phase extraction column of functionalized multi-walled carbon nanotube matrix, it is characterized in that the matrix of described solid-phase extraction column is the multi-walled carbon nanotube of functionalization, this functionalized Multi-walled carbon nanotubes (f-MWCNTs) are obtained by covalent chemical modification of original multi-walled carbon nanotubes through purification, carboxylation, acyl chloride, functionalization and other steps. The covalent chemical modification is carried out according to the following steps:

(1) Purification: reflux a certain quality of MWCNTs in 35% hydrochloric acid at 80 ℃ to 100 ℃ for 10 to 20 hours, filter with suction, wash with deionized water, and dry at 100 ℃ for 3 hours to obtain purified MWCNTs;

(2) Carboxylation: The purified MWCNTs were mixed with concentrated sulfuric acid:concentrated nitric acid = 3:1 by volume, refluxed at 80-100°C for 5 h, and the black solution after the reaction was diluted with deionized water and allowed to stand for separation. After layering, the upper acidic clear liquid was poured off; the precipitated MWCNTs-COOH was separated by vacuum filtration with a filter membrane, and washed with deionized water until neutral; the filtered product was dried in a vacuum drying oven at 50-80 °C for 3 h;

(3) Acyl chloride: Grind the dried MWCNTs-COOH into a single-necked round-bottomed flask filled with freshly steamed SOC1 ₂ and DMF, and reflux with magnetic stirring at 70°C-150°C for 20-30 h to carboxylate The MWCNTs-COOH is converted into acyl chloride multi-walled carbon nanotubes; after the reaction is completed, distillation or centrifugation removes excess SOC1 ₂ and DMF;

(4) Functionalization: After evaporating the product obtained in (3) to dryness, add ethyl p-aminobenzoate, stir and reflux in an oil bath for 20 to 50 hours; cool to room temperature, vacuum filter with a filter membrane, and use After washing with absolute ethanol, the product was dried overnight in a vacuum oven at 50-80°C to obtain the final functionalized multi-walled carbon nanotubes.

The solid-phase extraction column of the functionalized multi-walled carbon nanotube matrix of the present invention has a particle size of the multi-walled carbon nanotubes of 5-50 μm, an empty tube volume of the solid-phase extraction column of 1-6 mL, and a filling height of 0.6 ~ 1.2 cm, empty tube material is polyolefin.

The solid-phase extraction column of the functionalized multi-walled carbon nanotube matrix of the present invention, its preparation method is carried out according to the following sequence steps:

(1) Put a microporous polyethylene sieve plate into the bottom of the empty tube of the solid phase extraction column;

(2) Mix a certain amount of functionalized multi-walled carbon nanotubes with a certain amount of diatomaceous earth, and dry fill them into the column;

(3) Put another polyethylene sieve plate on the top of the mixture of functionalized multi-walled carbon nanotubes and diatomaceous earth;

(4) Compress the packing to keep the height of the packed column at 0.6-1.2 cm, and prepare a solid-phase extraction column.

Before loading the functionalized multi-walled carbon nanotubes into the column, the adsorbed water needs to be completely removed, which can be baked in a drying oven at 100 °C for 3 h.

The solid-phase extraction column of the functionalized multi-wall carbon nanotube matrix of the present invention needs to be pretreated with deionized water, ethyl acetate, acetone or methanol for purification and activation before use.

The filling principle of the f-MWCNTs SPE column of the present invention: both the solid phase extraction column tube and the sieve plate are produced in a standardized manner, and the height of the column tube and the thickness of the sieve plate are both fixed values. The solid phase extraction column of the present invention is actually adjusted by adjusting the diameter of the column. Adjust the volume of the contained liquid, so we choose different amounts of functionalized multi-walled carbon nanotubes according to different diameters, and control the filling height of f-MWCNTs in the solid-phase extraction column filled with functionalized multi-walled carbon nanotubes It is 0.8～1.2 cm, so as to ensure the column efficiency.

Different from the current solid-phase extraction column that uses a homogenate high-pressure packing method, the f-MWCNTs SPE column uses a packing height control method to ensure the density of the f-MWCNTs packing in the packed SPE column, and then control the flow rate. The specific process is to add a certain amount of f-MWCNTs and diatomaceous earth mixed filler into the solid phase extraction column, slowly press down the sieve plate, and constantly shake the small column during the pressing process to ensure that the f-MWCNTs in the small column is up and down. The filling density is consistent, so that the height of the filling is 0.8 to 1.2 cm.

In the present invention, functionalized multi-walled carbon nanotubes are used as the main filler, and diatomaceous earth is used as a carrier to make a solid phase extraction column. The packed f-MWCNTs SPE column is a polar solid phase extraction column, and its performance is similar to that of Compared with ordinary carbon nanotube SPE columns, because the f-MWCNTs SPE column has specific functional groups, its adsorption performance on target substances is stronger than that of ordinary carbon nanotube SPE columns, which plays a certain role in improving the recovery rate of target substances. Since the adsorption of substances by f-MWCNTs is reversible, the target substances can be eluted by adjusting the polarity of the elution solvent just like using a C ₁₈ SPE column. The usage methods of the two are very similar, even if activated with methanol or deionized water before use, the sample solution is also in the water phase, and the flow rate is controlled by adjusting the vacuum to make the solution pass through the SPE column at an appropriate flow rate, and the substance is retained on the SPE column , can be vacuum-dried to remove water, and the substance is rinsed and eluted with an organic solvent of appropriate polarity. It is mainly suitable for reverse phase extraction of non-polar to medium polar substances, and is used to enrich and purify target substances in samples.

The beneficial effects of the present invention are:

(1) It is inevitable to perform activation, purification, and elution operations when the solid-phase extraction column is used, so different solvents need to be used. When adding the solvent, it is required to change to a different solvent when the liquid level drops to the sieve plate. If the addition is too late, the filler will dry up and generate bubbles, which will affect the stability of the result; if the addition is too early, the added solvent will The solution mixed with the original solution on the frit, creating a new eluent with undesired polarity and unforeseen polarity, which reduces the reliability of the experimental results. However, the f-MWCNTs SPE column can avoid this problem, because the multi-walled carbon nanotubes have stronger adsorption to various solvents than ordinary packings, and maintain the wettability of the liquid surface for a long time, so that the operator has sufficient time to change to a different solvent.

(2) Compared with the traditional reversed-phase solid-phase extraction column MWCNTs SPE column, the f-MWCNTs SPE column has a large adsorption capacity, and can have a specific adsorption effect on specific substances, and can improve the recovery rate of target substances. The cost of multi-walled carbon nanotubes is low, the material is easy to obtain, and the commercialized solid-phase extraction empty column used is simple to prepare, easy to mass produce, and the cost is reduced. The functional experiment scheme is flexible and changeable, which increases the application range of f-MWCNTs SPE column .

(3) Due to the limitations of the f-MWCNTs SPE column preparation process, the particle size and length of the produced filler range from 5 to 100 μm, so the general packing effect is usually very tight. By adding a certain amount of diatomaceous earth, not only the flow rate It is faster than the general MWCNTs SPE column, and it is beneficial for the target substance to fully interact with f-MWCNTs in the f-MWCNTs SPE column, thereby improving the enrichment effect.

(4) When establishing the experimental method, some modifications can be made with reference to the existing use data of the non-polar SPE column, so that the system can be established as soon as possible.

Description of drawings

Figure 1 is a synthetic route diagram of functionalized multi-walled carbon nanotubes (f-MWCNTs).

Figure 2 is the f-MWCNTs SPE column enrichment and purification of paraben preservatives in cosmetics (spiked).

Peak information: (1) Methylparaben; (2) Ethylparaben; (3) Isopropylparaben; (4) Propylparaben; (5) Isopropylparaben; (6) Butylparaben.

Figure 3 is the enrichment and purification of paraben preservatives in cosmetics (unspiked) with f-MWCNTs SPE column.

Peak information: (3) Isopropylparaben.

Detailed ways

Below in conjunction with example the present invention is described in further detail.

A． Preparation of the extraction column

1. Empty column material and specification

The empty column specifications of existing solid phase extraction cartridges range from 0.05 g/1mL to 10 g/60mL. The material of the empty column is polypropylene, and there are polyethylene sieve plates with a pore size of 20 μm on the upper and lower sides of the small column. All the above-mentioned empty columns can be used in the present invention. In the following experimental examples, the present invention adopts 0.25-0.30 g/3mL.

2. Granularity (length) of MWCNTs

The packing particle size of the solid phase extraction column is generally 5-50 μm, and the pore size of the polyethylene sieve plate is 20 μm. In order to prevent the filler from flowing out from the sieve plate, we choose MWCNTs with a length of 5-50 μm as the modified raw material. Functional modification, the modified product f-MWCNTs is used as SPE matrix filler.

3. Selection of filling volume and filling height

The flow rate of the SPE column is related to the packing volume and packing height. The larger the filling volume, the higher the filling height, the slower the flow rate, and the correspondingly longer test time. According to this principle, for the f-MWCNTs SPE column, we choose to use the specification of 0.050-0.150 g/3 mL in terms of filling volume; in terms of filling height, we use a filling height of 0.8-1.2 cm (containing silicon algae).

the

Example 1

Use the aforementioned step A to fill a 3 mL solid phase extraction column with a packing height of 0.8-1.2 cm and a packing volume of 0.08-0.15 g/3 mL. Extraction of parabens in cosmetics using the solid-phase extraction column described above (spiked recovery and actual sample detection).

The f-MWCNTs SPE column needs to be pretreated with deionized water, ethyl acetate, acetone or methanol before use.

The specific process is as follows: 2 parts of 1 g cosmetic samples were weighed, 6 kinds of parabens standard preservatives were added to sample 1 (all 6 kinds of preservatives were added in an amount of 2.5 μg), and no standard substance was added to sample 2. Place samples 1 and 2 in two different centrifuge tubes, use mobile phase to make up to 5 mL respectively, and extract ultrasonically for 30 min. After the extract is properly diluted, filter it with a 0.5 μm filter membrane, and the filtrates of samples 1 and 2 are used for solid-phase extraction. Column loading. After the activation of the two f-MWCNTs SPE columns was completed, the above two filtrates were passed through the f-MWCNTs SPE columns respectively, and the flow rate was controlled at 3-5 mL/min. After all the filtrate passed through the SPE column, it was rinsed with 10 mL of deionized water, and the water was removed under pressure. Let it dry for 10 minutes, then start elution with 3 mL of methanol and collect the eluate, pressurize and dry it, then add 2 mL of methanol for a second elution and collect the eluate, and collect the two eluents together. The eluate was blown dry with concentrated nitrogen, dissolved by shaking with mobile phase, and the volume was adjusted to 200 μL for HPLC analysis. The HLPC chromatograms are shown in Figure 2 and Figure 3.

Figure 2 is the f-MWCNTs SPE column enrichment and purification of paraben preservatives in cosmetics (spiked).

Peak information: (1) Methylparaben; (2) Ethylparaben; (3) Isopropylparaben; (4) Propylparaben; (5) Isopropylparaben; (6) Butylparaben.

Figure 3 is the enrichment and purification of paraben preservatives in cosmetics (unspiked) with f-MWCNTs SPE column.

Peak information: (3) Isopropylparaben.

It can be seen from the figure that the f-MWCNTs SPE column has a good effect on the enrichment of 6 kinds of paraben ester preservative pollutants in cosmetics. Actual cosmetic sample testing. In Figure 2, it can be detected that the content of isopropylparaben in cosmetics is 0.52 μg/g.

Example 2

Use the aforementioned step A to fill a 6 mL solid phase extraction column with a packing height of 0.8-1.2 cm and a packing volume of 0.15-0.30 g/6 mL. The polycyclic aromatic hydrocarbons in purified water samples were enriched using the solid phase extraction column described above.

The f-MWCNTs SPE column is pretreated with deionized water, ethyl acetate, acetone or methanol before use.

The specific process is as follows: seawater and river water samples were collected respectively, the samples were centrifuged separately, 200 mL of the supernatant was taken, filtered with a 0.5 μm filter membrane, and the filtrate was transferred to a corresponding 200 mL volumetric flask. Take two packed 6 mL f-MWCNTs SPE columns, activate them with deionized water, ethyl acetate, acetone or methanol, let the above two filtrates pass through the f-MWCNTs SPE columns respectively, and control the flow rate under the vacuum pump to 3-5 mL/min. After all the filtrate passed through the SPE column, it was rinsed with 10 mL of deionized water, and the water was removed under pressure. Let it dry for 10 minutes, then use 2 mL of methanol to start elution and collect the eluate, pressurize and dry it, then add 1 mL of methanol for a second elution and collect the eluate, and collect the two eluents together. The eluate was blown dry with concentrated nitrogen. The residue was dissolved with 0.5 mL of n-hexane (analytical grade redistilled), and 2 μL was injected for GC analysis. The content of eight kinds of polycyclic aromatic hydrocarbons in river water samples was detected between 3.5 and 10.2 μg/L; no polycyclic aromatic hydrocarbons were detected in seawater samples. The recovery rate of actual water samples was between 89% and 95%.

Experimental Example 3 Use the method in step A above to fill a 6 mL solid-phase extraction column with a packing height of 0.8-1.2 cm and a packing volume of 0.15-0.30 g/6 mL. Neomycin residues were enriched in milk samples using the solid-phase extraction column described above.

The f-MWCNTs SPE column is pretreated with deionized water, ethyl acetate, acetone or methanol before use.

The specific process is as follows: Measure 10 mL of pure milk into a 15 mL polypropylene plastic centrifuge tube, add a certain volume of 10 μg/mL neomycin standard solution, shake evenly, and obtain a spiked milk sample containing a certain concentration of neomycin. Add 1 mL of 0.2 g/mL trichloroacetic acid solution, shake for 1 min, and centrifuge at 6000 g at 25 °C for 30 min. Carefully pipette 5 mL of the upper clear liquid for loading on the solid-phase extraction column. After the activation of the f-MWCNTs SPE column was completed, the supernatant was passed through the f-MWCNTs SPE column at a flow rate of 3-5 mL/min. After all the supernatant liquid passed through the SPE column, it was rinsed with 10 mL deionized water, and the water was dried under pressure. The cartridge was left to dry for 5 minutes. Finally, 1 mL of 0.3 mol/L HClO ₄ solution was used for elution twice and the eluate was collected. The eluate was blown dry with concentrated nitrogen, dissolved with mobile phase shaking, and the volume was adjusted to 200 μL for HPLC analysis. The spiked recoveries of neomycin in milk samples ranged from 93% to 101%.

Claims (3)

1. a solid-phase extraction column of a functionalized multi-walled carbon nanotube substrate, characterized in that the substrate of the solid-phase extraction column is a functionalized multi-walled carbon nanotube, the functionalized multi-walled carbon nanotube f- MWCNTs are obtained by covalent chemical modification of original multi-walled carbon nanotubes through the steps of purification, carboxylation, acyl chloride, and functionalization. The covalent chemical modification is carried out as follows: (1) Purification: reflux a certain quality of MWCNTs in 35% hydrochloric acid at 80 ℃ to 100 ℃ for 10 to 20 hours, filter with suction, wash with deionized water, and dry at 100 ℃ for 3 hours to obtain purified MWCNTs; (2) Carboxylation: The purified MWCNTs were mixed with concentrated sulfuric acid:concentrated nitric acid = 3:1 by volume, refluxed at 80-100°C for 5 h, and the black solution after the reaction was diluted with deionized water and allowed to stand for separation. After layering, the upper acidic clear liquid was poured off; the precipitated MWCNTs-COOH was separated by vacuum filtration with a filter membrane, and washed with deionized water until neutral; the filtered product was dried in a vacuum drying oven at 50-80 °C for 3 h; (3) Acyl chloride: Grind the dried MWCNTs-COOH into a single-necked round-bottomed flask filled with freshly steamed SOC1 ₂ and DMF, and reflux with magnetic stirring at 70°C-150°C for 20-30 h to carboxylate The MWCNTs-COOH is converted into acyl chloride multi-walled carbon nanotubes; after the reaction is completed, distillation or centrifugation removes excess SOC1 ₂ and DMF; (4) Functionalization: After evaporating the product obtained in (3) to dryness, add ethyl p-aminobenzoate, stir and reflux in an oil bath for 20 to 50 hours; cool to room temperature, vacuum filter with a filter membrane, and use After washing with absolute ethanol, the product was dried overnight in a vacuum oven at 50-80°C to obtain the final functionalized multi-walled carbon nanotubes. 2. The solid-phase extraction column of the functionalized multi-walled carbon nanotube matrix according to claim 1, the particle size of the multi-walled carbon nanotubes is 5-50 μm, and the empty tube volume of the solid-phase extraction column is 1-6 mL , the filling height is 0.6-1.2 cm, and the material of the empty tube is polyolefin. 3. according to the solid-phase extraction column of the functionalized multi-walled carbon nanotube matrix of claim 1 or 2, its preparation method is carried out in the following sequence steps: (1) Put a microporous polyethylene sieve plate into the bottom of the empty tube of the solid phase extraction column; (2) Mix a certain amount of functionalized multi-walled carbon nanotubes with a certain amount of diatomaceous earth, and dry fill them into the column; (3) Put another polyethylene sieve plate on the top of the mixture of functionalized multi-walled carbon nanotubes and diatomaceous earth; (4) Compress the packing to keep the height of the packed column at 0.6-1.2 cm, and prepare a solid-phase extraction column.

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