DGT binding film and preparation method and application thereof

Abstract

The invention discloses a DGT binding membrane as well as a preparation method and application thereof, and the DGT binding membrane comprises HLB (Hydrophile Lipophile Balance) and XAD18 (XAD18) in a mass ratio of (6.8-7.2): (2.8-3.2). Through the synergistic effect of the optimized compounding of the adsorption phase and the innovative design of the elution procedure, the technical performance (recovery rate and detection limit) is remarkably improved, and great advantages are shown in the aspects of convenience, economy and high efficiency of practical application; and a reliable and practical technical tool is provided for large-scale and high-standard water environment plastic additive monitoring.

Description

Technical Field

[0001] This invention relates to the field of DGT technology, and in particular to a DGT-binding membrane, its preparation method, and its application. Background Technology

[0002] Plastic additives in surface water environments, such as plasticizers, antioxidants, and flame retardants, have become emerging global pollutants. These compounds typically exist at trace or ultra-trace levels (ng / L to μg / L), but due to their endocrine disrupting, carcinogenic, and bioaccumulative properties, they pose a potential threat to aquatic ecosystems and human health. Accurate monitoring of the environmental concentrations of these pollutants is a prerequisite for conducting ecological risk assessments and pollution remediation. However, traditional active sampling techniques (such as instantaneous grab sampling) have significant limitations: First, commonly used grab sampling is instantaneous, only obtaining the water sample concentration at the moment of sampling. The concentration of plastic additives fluctuates greatly due to factors such as emissions, diurnal variations, rainfall runoff impact, and hydrological conditions. This makes it difficult for a single sampling result to accurately reflect its time-weighted average concentration, making it unsuitable for precise environmental risk assessment. In other words, existing sampling techniques cannot overcome the influence of pollutant concentration fluctuations over time, resulting in unrepresentative single sampling results. Second, the operation is cumbersome and costly. Commonly used grab sampling requires frequent field sampling and immediate transport of large amounts of water samples back to the laboratory for pretreatment and enrichment (such as solid phase extraction, SPE). The process is cumbersome, and pollution or degradation of the target substance can easily be introduced during transportation and storage. Moreover, the costs of manpower, resources, and time are high. Third, the detection limit is challenging. For ultra-trace pollutants, tens to hundreds of liters of water samples need to be collected and processed. The enrichment process is complex, with significant background interference, making it difficult to guarantee sensitivity and accuracy. Diffusive gradients in thin-films (DGT) is an in-situ passive sampling technique. Its basic principle is that the binding phase within the device can continuously and selectively adsorb target analytes through a diffusion gel layer, thereby enriching the time-weighted average concentration (TWA) over a period of time. This effectively overcomes the transient limitations of active sampling. DGT technology was initially successfully applied to the monitoring of metal ions, and its extension to the monitoring of organic pollutants is currently a research hotspot in environmental analysis. In recent years, researchers have experimented with various materials as binding phases for DGT devices to collect organic pollutants in water. Existing adsorbent materials, such as MOFs, suffer from poor water stability and high cost; MIPs suffer from template molecule leakage and slow kinetics; while functionalized resins and composite materials are generally limited by insufficient adsorption capacity, poor selectivity, or complex preparation processes. These limitations severely restrict their application in the complex environment of surface water for reliable and efficient passive sampling of trace plastic additives.Many passive samplers are based on the equilibrium principle, requiring accurate knowledge of the sampling rate (Rs) or the time to reach equilibrium. This is difficult to calculate precisely in complex and variable water environments, leading to large quantitative errors. Furthermore, currently available commercially available adsorption resin-based membranes have a narrow range of applicable pollutants, typically optimized for only a specific type of pollutant (such as hydrophobic persistent organic pollutants). There is a lack of a universal sampling medium that has high and known adsorption performance for a wide range of plastic additives with broad polarity.

[0003] Therefore, there is an urgent need to develop a DGT monitoring device capable of in-situ, sensitive, time-integrated, and passive sampling of organic pollutants, as well as a DGT binding membrane with high elution efficiency, so as to realize its practical application in large-scale environmental monitoring. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a DGT-binding membrane, its preparation method, and its applications. This invention aims to overcome the technical bottlenecks in the in-situ, passive collection of trace / ultra-trace organic plastic additives from surface water, enabling the monitoring of various plastic additives with significant polarity differences and extremely low concentrations (ng / L or even pg / L levels), while simultaneously providing sensitive and reliable passive sampling.

[0005] This invention provides a DGT-binding membrane comprising HLB and XAD18 in a mass ratio of (6.8-7.2):(2.8-3.2). This membrane creatively combines the excellent adsorption capacity of HLB resin for polar compounds with the high affinity of XAD-18 for hydrophobic compounds, thereby achieving simultaneous and efficient capture of a wide range of plastic additives with varying polarities. Compared to MOFs / COFs, which are complex to synthesize, expensive, and have questionable water stability, or MIPs, which pose a risk of template leakage, this membrane fully utilizes commercially available mature resins and boasts significant advantages such as low cost, simple and stable preparation process, and good reproducibility, making it highly suitable for large-scale environmental monitoring applications.

[0006] Furthermore, the method for preparing the binding membrane includes the following steps:

[0007] HLB powder and XAD18 powder were mixed at a mass ratio of (6.8-7.2):(2.8-3.2) to obtain resin powder. Then, agarose powder and resin powder were weighed at a mass ratio of (0.5-0.6):(3.9-4.2) and placed in a syringe. Methanol was added and the mixture was allowed to stand for 25-40 minutes for activation. Then, ultrapure water was added for rinsing. Weigh agarose powder and rinsed resin powder in a beaker at a mass ratio of (0.5-0.6):(3.9-4.2). Add ultrapure water and heat and stir to obtain a thermal gel solution. Pour the thermal gel solution into a preheated porous glass mold with a pouring thickness of 0.45-0.55 mm. Then cover with a glass plate and wait for the gel to cool to room temperature to obtain the binding membrane.

[0008] This invention also provides a DGT device, comprising a filter membrane, a diffusion membrane, and the aforementioned DGT binding membrane. The key to this DGT device lies in utilizing a specific binding phase with high adsorption capacity and strong binding force for target organic matter. The special binding membrane employs both the hydrophilic-lipophilic balance of HLB and the superhydrophobicity of XAD-18. The resulting device can effectively enrich most types (wide polarity range) of plastic additives. Furthermore, this specific DGT device overcomes the problem of unrepresentative monitoring results caused by fluctuations in plastic additive concentration over time in traditional active sampling methods (such as instantaneous grab sampling). It also simplifies the sampling process, reduces dependence on on-site power supplies, frequent maintenance, and expensive instruments, enabling long-term, continuous, and power-free monitoring.

[0009] Furthermore, the filter membrane is a hydrophilic PTFE membrane.

[0010] Furthermore, the method for preparing the diffusion film includes the following steps: Dissolve agarose powder in ultrapure water, then heat and stir thoroughly until the solution becomes clear to obtain a thermogel solution. Pour the thermogel solution into a preheated porous glass mold with a pouring thickness of 0.75-0.85 mm, cover with a glass plate, and wait for the gel to cool to room temperature to obtain the diffusion membrane.

[0011] Furthermore, the porous glass mold is a six-hole glass mold.

[0012] The present invention also provides the application of the DGT device in the field of organic pollutant monitoring.

[0013] Furthermore, the application includes an adsorption process and an elution process, wherein the elution process involves removing the binding membrane from the DGT device after the adsorption process and placing it in an eluent for ultrasonic elution.

[0014] Furthermore, the elution procedure uses a solution with an acetonitrile:ethyl acetate:acetone volume ratio of (9.8-10.3):(2.9-3.2):(1.9-2.2). Specifically, acetonitrile is first added and sonicated for 13-16 min. After removing the acetonitrile eluent, a mixed solution of ethyl acetate and acetone is sonicated for another 13-16 min. The two eluents are then mixed and the solution is brought to a final volume using nitrogen blowing. The multi-program sequential elution strategy employed in this invention perfectly complements the broad-spectrum adsorption characteristics of the HLB / XAD-18 mixed membrane. This method, through a progressively polar organic solvent system, efficiently desorbs various plastic additives from weakly polar to strongly polar substances sequentially, fundamentally overcoming the drawbacks of incomplete elution with a single solvent. This completely transforms the high capacity advantage of the adsorbent into actual recovery, significantly reducing the method detection limit and improving the accuracy of monitoring data.

[0015] Furthermore, the organic pollutant is any one or more of plasticizers, antioxidants, and flame retardants.

[0016] Furthermore, the organic pollutant is any one or more of phthalate ester additives (PAEs), organophosphate additives (OPEs), bisphenol A additives (BPA), etc.

[0017] In summary, compared with the prior art, the present invention achieves the following technical effects: (1) The DGT-binding membrane provided by the present invention can adsorb a variety of plastic additives in water and can be successfully applied to the field of DGT technology, solving the technical problem that the existing technology cannot perform in-situ, sensitive, time-integrated sampling of a variety of pollutants and ensure passive sampling. (2) The DGT binding membrane provided by the present invention achieves efficient capture of a wide range of plastic additives with broad polarity. (3) The DGT binding membrane provided by the present invention makes full use of commercially available mature resins and has the outstanding advantages of low cost, simple and stable preparation process and good reproducibility, making it very suitable for large-scale environmental monitoring applications. (4) The multi-program sequential elution strategy adopted by the DGT device provided by the present invention fundamentally overcomes the drawback of incomplete elution by a single solvent, thereby completely converting the high capacity advantage of the adsorbent into actual recovery rate, significantly reducing the method detection limit and improving the accuracy of monitoring data. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is an adsorption kinetic diagram of organophosphorus compounds by the DGT device in Embodiment 1 of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] Example The present invention will be further illustrated below with reference to specific embodiments and comparative embodiments. The following specific embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the following embodiments, and are not in particular limited to the types of raw materials used in the following specific embodiments.

[0022] I. The sources of raw materials for the examples and comparative examples are as follows: Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this invention are commercially available.

[0023] II. Performance Testing Methods (1) Adsorption capacity test: The adsorption capacity was determined by immersing the bound gel in 20 mL of a solution with a concentration of 500 μg / L. - The adsorption was carried out in a solution of ¹ (solution conditions: ionic strength IS = 0.01 M NaCl, pH = 6.5 ± 0.2) and shaken at 150 rpm for 24 hours at 25 ± 0.2℃. Samples were taken every 1 h, and the adsorption amount was calculated as a function of time. The adsorption amount of the target plastic additive on the resin was calculated based on the mass conservation principle by the difference in solution concentration before and after the experiment.

[0024] (2) Saturated adsorption capacity test: The DGT device was placed in 40 mL of 0.01 M NaCl with concentration gradients of 20, 50, 100, 150, 200, 250, and 500 μg / L. - ¹The target drug solution was shaken at 150 rpm for 24 hours at 25 °C, and the saturated adsorption capacity was determined.

[0025] (3) Elution efficiency test: The DGT device was placed in 10 mL of 100 μg L⁻¹ target drug solution containing 0.01 M NaCl, and 100 ng of internal standard was added to the solution. The solution was oscillated at 150 rpm for 24 hours at a constant temperature of 25℃. The mass difference of the target drug in the solution before and after adsorption (i.e., the mass of the target drug adsorbed by the binding membrane) was recorded as M0. The binding membrane was removed and ultrasonically eluted. The eluent was filtered through a 0.45 μm hydrophilic PTFE filter membrane. After nitrogen blowing to a fixed volume, the mass of the eluted target drug was recorded as M1. The elution efficiency f e for .

[0026] (4) Limit of Detection Test: At least 7 assembled DGT devices were placed in 40 mL of ultrapure water and shaken at 150 rpm for 24 hours at 25°C. After removing the binding membrane, ultrasonic elution was performed. The eluent was collected, purged with nitrogen, and an internal standard was added and the volume was adjusted. The concentrations of the 7 blank samples were measured as C1, C2...C7. The arithmetic mean was calculated as x, and the standard deviation was SD. The limit of detection of the eluent was IDL = 3 × SD. The limit of detection of DGT in actual water bodies (MDL) was calculated as follows. DGT =IDL×Velution) / (A×t×D). Where Velution is the final volume of the eluent, A is the DGT window exposure area, t is the sampling time, and D is the diffusion coefficient of the target substance.

[0027] Example 1 Example 1 provides a DGT device 1, including a diffusion membrane, a PTFE filter membrane, and a binding membrane: The diffusion membrane was prepared as follows: 0.6 g of agarose was dissolved in 40 mL of ultrapure water, then heated and stirred thoroughly until the solution became clear and transparent, thus preparing a 1.5% agarose solution. The thermogel solution was immediately poured into a preheated six-well glass mold, with each well having an area of ​​approximately 3.14 cm². 2 The thickness of the casting is 0.8 mm. Then, a glass plate is quickly placed on top to ensure that the gel surface is flat and a diffusion film is obtained. After the diffusion gel cools to room temperature, the glass plate is removed, the agarose gel is carefully taken out, and it is placed in ultrapure water for storage. The membrane was prepared as follows: XAD18 was pre-milled and then passed through a 200-400 mesh sieve to obtain XAD18 powder. HLB powder was extracted from an HLB solid-phase extraction column. Agarose powder and resin powder (HLB powder:XAD18 powder = 7:3) were weighed at a mass ratio of 0.6:4 and placed in a 100 mL disposable syringe (with a suitably sized glass fiber filter membrane pre-placed at the bottom). A certain amount of methanol was added, and the mixture was allowed to stand for 30 minutes for activation. Then, an appropriate amount of ultrapure water was added for rinsing until the methanol was completely removed to remove any impurities and enhance hydrophilicity. Approximately 4 g of the rinsed resin powder was weighed into a 100 mL glass beaker, and 0.6 g of agarose powder was added. 40 mL of ultrapure water was then measured into the beaker using a 50 mL graduated cylinder. The mixture was heated and stirred, and the hot gel solution was immediately poured into a preheated six-well glass mold, with each well having an area of ​​approximately 3.14 cm². 2 The thickness of the casting is 0.5 mm, and then a glass plate is quickly placed on top to ensure that the gel surface is flat and a binding membrane is obtained. The amount of resin added in each binding membrane is about 35-40 mg. The adsorption behavior of 10 organophosphates on the binding membrane was investigated through kinetic experiments: The binding membrane was placed in 50 mL of a 100 μg L⁻¹ target drug solution containing 0.01 M NaCl, ensuring complete immersion. It was then placed in a constant-temperature shaker at 25°C and 200 rpm. Samples were collected at different time intervals (5 min, 15 min, 30 min, 60 min, 2 h, 4 h, 5 h, 6 h, 19 h, 20 h, 24 h). The shaker temperature was set to 30°C and the shaking speed to 200 rpm. To ensure data accuracy and reliability, three parallel samples were set for each time gradient. The mass of OPEs adsorbed by the binding membrane was then measured, and the adsorption amount over time was plotted. The experimental results are shown below. Figure 1 As shown, under the condition of an initial OPE mass of 5000 ng, the adsorption capacity of the binding membrane for OPEs increased rapidly in the first 200 min, corresponding to a high average adsorption rate. Subsequently, the growth rate of adsorption capacity gradually slowed down and tended to stabilize at around 6 h. Although the adsorption trend was similar, the maximum adsorption capacity for different OPEs was different. The maximum adsorption capacity for TnBP and TPrP was the largest, reaching about 450 ng. The maximum adsorption capacity for TDICP, TCIPP, TCEP, TiBP and other substances was about 3500 ng, while the maximum adsorption capacity for TMP and TEHP was about 1000 ng. The results show that the maximum adsorption capacity of the DGT binding membrane of the present invention for various OPEs is higher than the concentration of various OPEs in the environment, and it can measure the concentration of OPEs in the environment better. Field verification of the DGT device in Example 1: The DGT device and active sampling device of the present invention were deployed in a surface water basin and monitored continuously for 7 days. The time-weighted average concentration measured by DGT was in good agreement with the average value of multiple measurements by active sampling (P>0.05), and it was able to capture concentration fluctuation peaks that were not detected by active sampling, which confirmed the applicability and reliability of the field application.

[0028] Comparative Example 1 Comparative Example 1 provides a DGT device 2, which differs from Example 1 in that the binding membrane is a pure HLB gel.

[0029] Comparative Example 2 Comparative Example 2 provides a DGT device 3, which differs from Example 1 in that the binding membrane is a pure XAD18 gel.

[0030] Table 1. Adsorption-desorption effects of different DGT devices

[0031] Example 2 Example 2 is the elution procedure for the DGT device of the present invention: First, add 10 mL of acetonitrile and sonicate for 15 min. After removing the acetonitrile eluent, sonicate again with a mixture of 3 mL of ethyl acetate and 2 mL of acetone for 15 min. Mix the two eluents to obtain 15 mL of eluent, and then bring the volume to a final volume using nitrogen blowing.

[0032] In Example 1, a specific membrane was used to prepare the DGT device, and a specific elution program was combined to obtain a DGT monitoring scheme with both excellent adsorption and elution efficiency. Because a single adsorption phase (such as pure HLB) strongly adsorbs highly hydrophobic additives (such as long-chain phthalates and certain UV stabilizers), while a single hydrophobic phase (such as pure XAD-18) strongly adsorbs highly polar additives (such as triphosphates), it is difficult to completely elute them using a single solvent (such as methanol or acetonitrile), resulting in low and unstable recovery rates, which directly leads to high method detection limits and systematic biases in the monitoring data. Compared with DGT devices using a single adsorption phase (such as pure HLB membranes or XAD series resin membranes), the DGT device obtained by this invention can passively collect organic pollutants in water and has a flow rate adsorption effect on plastic additives with a wide range of polarities. Combined with a gradient elution program, it can simultaneously improve elution efficiency while adsorbing a wide range of polar additives, thereby significantly reducing the method detection limit (MDL) and solving the problems of low recovery rate and inaccurate monitoring data in existing technologies.

[0033] The data above show that the DGT device of this invention can adsorb more than a dozen typical plastic additives with log Kow values ​​ranging from 1.5 (e.g., triphenyl phosphate) to 7.5 (e.g., UV-329 UV absorber). Furthermore, the average elution recovery rate has been steadily increased from 60-80% in existing technologies to 85-105%. This stable and high recovery rate significantly improves the signal-to-noise ratio (S / N) of the final instrument analysis. Calculations show that the method detection limit (MDL) is generally reduced by 30%-50%, meaning that this invention can detect pollutants at lower concentrations, greatly improving the sensitivity and accuracy of monitoring. In contrast, DHT devices using other membrane-bound methods can only monitor a small range of polar pollutants. Therefore, to monitor multiple pollutants with vastly different polarities, it may be necessary to deploy multiple DGT devices with different adsorption phases or perform multiple elution procedures. This not only doubles the field workload but also significantly increases the time and solvent consumption costs of laboratory analysis. Therefore, the combination of the specific DGT device and the matching elution program of the present invention, compared with the prior art's approach of using a single adsorption phase and a single elution program, can achieve significant progress in technical performance (recovery rate, detection limit) through the synergistic effect of optimized adsorption phase compounding and innovative elution program design. It also demonstrates great advantages in terms of convenience, economy and efficiency in practical application, providing a reliable and practical technical tool for conducting large-scale, high-standard monitoring of plastic additives in the water environment.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A DGT-binding membrane, characterized in that, The binding membrane comprises HLB and XAD18 in a mass ratio of (6.8-7.2):(2.8-3.2).

2. The DGT-binding membrane according to claim 1, characterized in that, The method for preparing the binding membrane includes the following steps: HLB powder and XAD18 powder were mixed at a mass ratio of (6.8-7.2):(2.8-3.2) to obtain resin powder. Then, agarose powder and resin powder were weighed at a mass ratio of (0.5-0.6):(3.9-4.2) and placed in a syringe. Methanol was added and the mixture was allowed to stand for 25-40 minutes for activation. Then, ultrapure water was added for rinsing. Weigh agarose powder and rinsed resin powder in a beaker at a mass ratio of (0.5-0.6):(3.9-4.2). Add ultrapure water and heat and stir to obtain a thermal gel solution. Pour the thermal gel solution into a preheated porous glass mold with a pouring thickness of 0.45-0.55 mm. Then cover with a glass plate and wait for the gel to cool to room temperature to obtain the binding membrane.

3. A DGT device, characterized in that, Includes filter membranes, diffusion membranes, and DGT binding membranes as described in any one of claims 1-2.

4. The DGT device according to claim 3, characterized in that, The filter membrane is a hydrophilic PTFE membrane.

5. The DGT device according to claim 3, characterized in that, The method for preparing the diffusion film includes the following steps: Dissolve agarose powder in ultrapure water, then heat and stir thoroughly until the solution becomes clear to obtain a thermogel solution. Pour the thermogel solution into a preheated porous glass mold with a pouring thickness of 0.75-0.85 mm, cover with a glass plate, and wait for the gel to cool to room temperature to obtain the diffusion membrane.

6. The DGT device according to claim 5, characterized in that, The porous glass mold is a six-hole glass mold.

7. The application of the DGT device according to any one of claims 3-6 in the field of organic pollutant monitoring.

8. The application according to claim 7, characterized in that, It includes an adsorption process and an elution process, wherein the elution process involves removing the binding membrane from the DGT device after the adsorption process and placing it in an eluent for ultrasonic elution.

9. The application according to claim 8, characterized in that, The elution process uses a solution with a volume ratio of acetonitrile:ethyl acetate:acetone of (9.8-10.3):(2.9-3.2):(1.9-2.2).

10. The application according to claim 7, characterized in that, The organic pollutant is any one or more of plasticizers, antioxidants, and flame retardants.

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