CN108421280B - A kind of thiolated organic-inorganic hybrid monolithic column and its preparation method and use - Google Patents

Abstract

A thiol-functional organic-inorganic hybrid monolithic column, which is a thiol-functional organic-inorganic hybrid capillary monolithic column synthesized by a one-step copolycondensation method. The thiol groups on the surface of the monolithic material can selectively adsorb As(III), and the needle-type solid-phase microextraction device of the monolithic column can selectively extract As(III) in a wide pH range, without the retained As( V) is directly collected; then the adsorbed As(III) is eluted with nitric acid/potassium iodate solution and collected and measured to realize the separation and analysis of the two inorganic arsenic species. Compared with other sulfhydryl monolithic column materials, this method adopts the "one-step method", which is easy to prepare, has good reproducibility, and makes the distribution of sulfhydryl groups more uniform and has good mechanical strength; The treatment can be used for the collection, separation and analysis of on-site water samples.

Description

A kind of thiolated organic-inorganic hybrid monolithic column and its preparation method and use

Technical field:

The invention relates to a sulfhydryl-functionalized organic-inorganic hybrid monolithic column for speciation analysis of inorganic arsenic, in particular to a novel sulfhydryl-functionalized monolith obtained by "one-step" synthesis based on a novel ternary weak alkaline solution system The solid-phase microextraction device constructed by column material and needle solid-phase microextractor was used for the separation and analysis of As(III) and As(V).

Background introduction:

As a widespread trace element, arsenic can cause serious damage to the entire ecosystem and human health. At present, arsenic pollution in soil, groundwater and drinking water has become a worldwide problem. Arsenic mainly comes from arsenic-containing sediments, metallurgy, pesticides, fertilizers, coal combustion and industrial wastewater discharge. Studies have shown that the toxicological behavior of arsenic is closely related to its existing form. Generally, the toxicity of inorganic arsenic is greater than that of organic arsenic, and the toxicity of trivalent arsenic (As(III)) in inorganic arsenic is significantly greater than that of pentavalent arsenic (As(V). )). In environmental water, the most important form of arsenic is inorganic arsenic, which is the most harmful. The World Health Organization (WHO) limit for arsenic in drinking water is 10 μg/L, which is lower than the detection limit of the existing conventional trace element analyzers, while the concentration of As(III) in drinking water The limit is relatively lower, and most element detection instruments can only measure the total amount and cannot distinguish between different forms. Therefore, it is of great significance to develop a simple and practical method for pre-separation and enrichment of inorganic arsenic species in water.

As(III) and As(V) are not stable in nature, and may undergo interconversion in oxidative or reducing matrices. At present, water samples generally need to be collected and transported back to the laboratory for analysis. Sample transportation and storage require a long time, and usually require time-consuming pretreatment. These processes increase the risk of arsenic transformation. Therefore, it is of great significance to develop a simple method to complete the sample pretreatment at the sampling site.

The shortcomings of the existing methods for preparing thiol-organic-inorganic hybrid monolithic columns: due to the weak acidity of thiol reagents, it is difficult to directly prepare thiol-containing monolithic columns. Therefore, the existing thiol-functional organic-inorganic hybrid There are two main ways to prepare monolithic columns: one is to introduce sulfhydryl groups into the surface of the prepared monolithic column skeleton by post-modification; or to mix sulfhydryl-containing silane reagents with tetraethoxy/methoxysilane reagents , firstly hydrolyzed under acidic conditions and then polymerized by adding alkaline reagents. However, these two most commonly used methods still have certain problems: in the materials obtained by the post-modification method, the sulfhydryl groups only exist on the surface of the whole material, and the uniformity of the distribution of functional groups cannot be guaranteed, and the reproducibility is low. In the second method, when the alkaline reagent is added, the polymerization is very rapid, so that the bonding between the monolithic material and the capillary wall is not strong enough, and the monolithic column material is prone to peeling off, which affects the service life. At the same time, both of the current two methods have problems such as cumbersome operation and time-consuming.

Disadvantages of the existing solid phase extraction device: the existing solid phase extraction device usually fills the material into a section of empty tube (such as glass tube, polytetrafluoroethylene tube, or stainless steel tube, etc.) Stuff the glass wool at both ends to secure the material. This preparation method has the following problems: first, the resulting solid-phase extraction column has a high column pressure, especially when a smaller size packing material and a larger flow rate are used; second, the consistency of packing glass wool cannot be guaranteed, This results in poor reproducibility of the prepared solid phase extraction column.

Invention content:

The invention provides a new idea for preparing a thiolated organic-inorganic hybrid monolithic column and is used for rapid separation and analysis of inorganic arsenic forms, in particular to a preparation method for preparing a thiol hybrid monolithic column by a "one-step method"; A method for the separation and analysis of inorganic arsenic forms by a needle-type solid-phase microextraction device.

The technical scheme of the present invention is as follows:

A thiolated organic-inorganic hybrid monolithic column is prepared as follows:

Add 33.3 mg of cetyltrimethylammonium bromide (CTAB) to a mixture of 130 μL of ethanol, 173 μL of isopropanol and 152 μL of 10% ammonia water, vortex until the solid is completely dissolved and the solution is clear and transparent, then take 300 μL of tetraethyl acetate Oxysilane (TEOS) and 100 μL mercaptopropyltrimethoxysilane (MPTMS) were added to the above transparent solution, mixed by vortex, sonicated in ice water at 0 °C for 30 s, and then injected into the activated capillary, and the two capillaries were separated. After end-sealing, heat in a 45 °C water bath for 20 h, and after cooling to room temperature, the monolithic column was washed with methanol and water in turn to remove unreacted reagents and template CTAB, and then the thiolated organic-inorganic hybrid monolithic column was stored in 4 ℃ refrigerator for later use, the schematic diagram of the reaction is shown in Figure 1.

The obtained thiolated organic-inorganic hybrid monolithic column material has a specific surface area of 68.51m ² /g, an average pore diameter of 7.124nm, a S content of 3.31±0.02mmol/g, and an adsorption capacity of 2.32μg/g for trivalent arsenic. cm.

A needle-type solid-phase microextractor using the above-mentioned thiolated organic-inorganic hybrid monolithic column is prepared by the following method: selecting a syringe needle with a suitable size, discarding the metal needle, retaining only the base part, and intercepting a 5cm long The above-mentioned thiolated organic-inorganic hybrid monolithic column can replace the original metal needle and fix it, that is, a needle-type solid-phase microextractor is prepared, as shown in Figure 2.

The application of the above-mentioned thiolated organic-inorganic hybrid monolithic column in the separation and enrichment of inorganic arsenic.

A method for separation, enrichment and analysis of inorganic arsenic, which comprises the following steps:

Step 1. Adjust the sample to be tested to pH 4.0 with 1% (v/v) dilute nitric acid, take a certain volume of the sample solution (the volume is denoted as V), and pass through the thiolated organic-inorganic hybrid at a flow rate of 200 μL min ^-1 At this time, the trivalent arsenic was selectively adsorbed on the thiolated organic ^- inorganic hybrid monolithic column, while the pentavalent arsenic was not retained and flowed out directly. 3% (v/v) nitric acid (containing 0.01M potassium iodate) was passed through the thiolated organic-inorganic hybrid monolithic column, at which time trivalent arsenic was eluted, and the eluate was collected, and the enrichment factor was V/200 μL;

Step 2. Determination of pentavalent arsenic and trivalent arsenic

Select appropriate detection instruments (such as inductively coupled plasma mass spectrometry, inductively coupled plasma spectroscopy, atomic absorption spectrophotometer, etc.) to measure the concentration of arsenic in the above-mentioned sample solution, sample effluent and eluent respectively. The obtained arsenic concentration divided by the enrichment factor is the actual trivalent arsenic concentration in the sample, while the pentavalent arsenic concentration in the sample can be obtained by directly measuring the arsenic concentration in the sample effluent, or by measuring the total arsenic in the original sample solution. The concentration is then obtained by subtracting the trivalent arsenic concentration.

The innovation of the present invention is:

First, for the first time, a ternary weakly alkaline solvent was used to synthesize a thiol-functional organic-inorganic hybrid monolithic column by a "one-step method". The preparation was simple and the reproducibility was good. Valence arsenic.

Second, using a self-made needle-type solid-phase micro-extractor for solid-phase micro-extraction, the method is simple to prepare, uses small column pressure, and has high adsorption efficiency.

Third, the enriched As(III) is eluted by nitric acid/potassium iodate to realize the separation and enrichment of As(III) in the sample, and the As(III) in the sample can be obtained by directly measuring the arsenic concentration in the sample effluent after adsorption. V) concentration, or calculate the As(V) concentration using the subtraction method.

Description of drawings

Figure 1 is a schematic diagram of the synthesis of materials;

Figure 2 Needle solid phase microextractor;

Figure 3 Fourier transform infrared spectrum of the material;

Figure 4 Raman spectrum of the material;

Figure 5 is a scanning electron microscope image of the material;

6 is a schematic diagram of a solid-phase extraction device and the steps of morphological analysis.

Detailed ways

Application example, taking two actual environmental water samples as examples, Yangtze River water and rainwater, both collected from Nanjing, Jiangsu Province, after passing through a 0.45 μm filter membrane, the concentration of inorganic arsenic forms in them was measured. The steps are shown in Figure 6.

1. Material synthesis

Raw materials: tetraethoxysilane (TEOS), mercaptopropyltrimethoxysilane (MPTMS), cetyltrimethylammonium bromide (CTAB)

Specific steps: activate the capillary first: cut a capillary of a certain length, rinse it with 1M NaOH solution (12h), water (30min), 1M hydrochloric acid solution (12h), water (30min), methanol (30min) in sequence, and then rinse with nitrogen Blow dry, set aside. Add 33.3 mg CTAB to a mixture of 130 μL ethanol, 173 μL isopropanol and 152 μL 10% ammonia water, vortex to dissolve the solid until the solution is clear and transparent, add 300 μL TEOS and 100 μL MPTMS to the above transparent solution, and vortex for 30 s to mix. , ultrasonicated for 30 s in an ice-water bath at 0 °C, passed into the activated capillary tube, sealed both ends of the capillary tube, and heated in a water bath at 45 °C for 20 h. After the reaction was completed, it was cooled to room temperature, and the monolithic column was washed with methanol and water in turn to remove unreacted reagents and template CTAB, and then the thiolated organic-inorganic hybrid monolithic column was stored in a 4°C refrigerator for future use. The obtained thiolated organic-inorganic hybrid monolithic column material has a specific surface area of 68.51m ² /g, an average pore diameter of 7.124nm, a S content of 3.31±0.02mmol/g, and an adsorption capacity of 2.32μg/g for trivalent arsenic. cm. The infrared spectrum of the material is shown in FIG. 3 , the Raman spectrum is shown in FIG. 4 , and the scanning electron microscope image is shown in FIG. 5 .

2. Construction of a needle-type solid-phase microextractor

Choose a syringe needle of the proper size, discard the metal needle, and keep only the base part. Cut off a thiolated organic-inorganic hybrid monolithic column with a length of 5 cm, replace the original metal needle and fix it.

3. Separation and enrichment of inorganic arsenic

First, the sample to be tested was adjusted to pH 4.0 with dilute nitric acid, and 4 mL of the sample solution was taken and passed through the monolithic column at a flow rate of 200 μL min ⁻¹ . At this time, trivalent arsenic can be selectively adsorbed on the thiol monolith, while pentavalent arsenic is not retained and directly flows out. The sample effluent is collected, and then 200 ^μL of 3% (v/v) Nitric acid (containing 0.01M potassium iodate) was passed through the monolithic column at which point the trivalent arsenic was eluted and the eluate was collected. The enrichment factor is 4 mL/200 μL=20 times.

4. Determination of pentavalent arsenic and trivalent arsenic

The above-mentioned sample solution, sample effluent and eluent after separation and enrichment were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and ⁷⁵ As was selected to be determined. The concentrations of pentavalent arsenic and trivalent arsenic in the sample solution were obtained respectively. (Note: The enrichment factor and detection method can be based on their own experimental conditions. If the sensitivity of the detection instrument is not enough, the enrichment factor can be appropriately increased; if the sensitivity of the detection instrument is sufficient, the enrichment factor can be appropriately reduced.)

Table 1. Sample Measurement Results Data Sheet

It can be seen from the above table that the concentration accuracy of the two arsenic forms measured by this method is high and the recovery rate is good.

The "one-step method" was used to prepare the thiolated organic-inorganic hybrid monolithic column, which is simple in operation, good in reproducibility, more uniform in the distribution of thiol groups, and good in mechanical strength; the thiolated organic-inorganic hybrid monolithic column can selectively adsorb the three Valence arsenic can realize rapid separation and enrichment of inorganic arsenic species in water; at the same time, the required equipment is simple and easy to use, which can meet the sample pretreatment under various conditions, and can realize on-site separation and enrichment of arsenic species in water samples.

Claims (3)

1. a thiolated organic-inorganic hybrid monolithic column is characterized in that: it is prepared as follows: Add 33.3 mg cetyltrimethylammonium bromide (CTAB) to a mixture of 130 μL ethanol, 173 μL isopropanol and 152 μL 10% ammonia water, vortex until the solid is completely dissolved and the solution is clear and transparent, then take 300 μL tetraethoxylate Silane (TEOS) and 100 μL of mercaptopropyltrimethoxysilane (MPTMS) were added to the above transparent solution, mixed by vortex, ultrasonicated in ice water at 0 °C for 30 s, and injected into the activated capillary. After sealing, heat in a water bath at 45 °C for 20 h, and after cooling to room temperature, the monolithic column was washed with methanol and water in turn to remove unreacted reagents and template CTAB, and then the thiolated organic-inorganic hybrid monolithic column was stored at 4 °C Reserve in refrigerator. 2. a needle-type solid-phase microextractor adopting the thiolated organic-inorganic hybrid monolithic column of claim 1, characterized in that it is prepared as follows: choose a syringe needle with a suitable size, discard the metal needle, and only Retain the base part, cut the above-mentioned thiolated organic-inorganic hybrid monolithic column with a length of 5cm, replace the original metal needle and fix it, namely, a needle-type solid-phase microextractor is obtained. 3. The application of the thiolated organic-inorganic hybrid monolithic column according to claim 1 in the separation, enrichment and analysis of inorganic arsenic.

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