Separation and detection of trace atrazine from seawater using dummy-template molecularly imprinted solid-phase extraction followed by high-performance liquid chromatography

Molecularly imprinted polymer for solid-phase extraction of oleanolic acid from Ligustrum lucidum fruit

A molecularly imprinted polymer (MIP) was synthesized for the selective extraction of oleanolic acid (OA), employing OA as the template molecule, acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross-linking agent, azobisisobutyronitrile as the initiator, and chloroform as the porogenic solvent. The characterization of the obtained MIPs was evaluated by scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy. The MIPs reached adsorption equilibrium within 2 hours to OA, with high adsorption capacity of 124.68 mg/g. Subsequently, these MIPs were packed in empty solid-phase extraction (SPE) cartridge to enrichment OA from Ligustrum lucidum fruit extract. The parameters of SPE were optimized as follows: loading 0.5 ml of a 1.0 mg/ml OA reference solution, washing with 0.5 ml of toluene, and eluting with 4 ml of methanol. Under these conditions, the enrichment rate of OA from L. lucidum extract reached 76.0%. Additionally, an high-performance liquid chromatography method for determining OA content was validated. This study provides an effective approach for the separation and enrichment of OA from complex matrices and also provides practical feasibility for the separation and enrichment of other triterpenoids.

Sensitive extraction of seven pesticide residues from environmental water with magnetic graphene oxide-based covalent organic framework

The use of pesticides has increased with the development of agriculture. However, due to the trace content and the matrix's inherent complexity in environmental water, development of rapid and sensitive detection method present significant challenges in the analysis of pesticide residues. The study synthesized magnetic graphene oxide (MGO) by combining superparamagnetic nanoparticles with the easy modification of graphene oxide (GO). Covalent organic frameworks (COFs) were then modified to have a large specific surface area. Finally, magnetic graphene oxide-based covalent organic frameworks, namely MGO-COFs, were obtained with a spherical structure and used as magnetic solid-phase extraction materials, which was successfully used to determine the seven pesticide residues in environmental samples in conjunction with high performance liquid chromatography. The method has a wide linear range for the tested pesticides, with satisfactory correlation coefficients (R ≥ 0.099) and low detection limits (0.3-1.21 μg L-1). The correlation coefficients for all seven pesticides were high (R2 ≥ 0.9996). The spiked recoveries, exhibiting a range of 91.3 to 109 %, demonstrated that the developed MGO-COF-MSPE-HPLC-UV method is simple, efficient, and suitable for the analysis and detection of seven pesticide residues in environmental water.

A double-emission molecularly imprinted ratiometric fluorescent sensor based on carbon quantum dots and fluorescein isothiocyanate for visual detection of p-nitroaniline

A novel molecularly imprinted ratiometric fluorescent sensor CQDs@MIP/FITC@SiO2 for the detection of p-nitroaniline (p-NA) was constructed through the mixture of CQDs@MIP and FITC@SiO2 in the ratio of 1:1 (VCQDs@MIP:VFITC@SiO₂). The polymers of CQDs@MIP and FITC@SiO2 were prepared by sol-gel method and reversed-phase microemulsion method, respectively. CQDs@MIP was used as the auxiliary response signal and FITC@SiO2 was used as the reference enhancement signal. The signal was measured at excitation/emission wavelengths of 365/438, 512 nm. The sensor showed good linearity in the concentration range 0.14-40.00 µM (R2 = 0.998) with a detection limit of 0.042 µM for p-NA. The color change of "blue-cyan-green" could be observed by the naked eye under 365 nm UV light, thus realizing the visual detection of p-NA. The sensor presented comparable results compared with high-performance liquid chromatography (HPLC) method for the detection of p-NA in hair dye paste and aqueous samples with recoveries of 96.8-103.7% and 95.8-104.4%, respectively. It was demonstrated that the constructed sensor possesses the advantages of simplicity, excellent selectivity, superior sensitivity, and outstanding stability.

Quantification of 2,4-dichlorophenoxyacetic acid in environmental samples using imprinted polyethyleneimine with enhanced selectivity as a selective adsorbent in ambient plasma mass spectrometry

Detection and quantification of various organic chemicals in the environment is critical to track their fate and control their levels. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a widely applied phenoxy herbicide with potential toxicity to fish and other aquatic organisms. In this study, we address the need for improved detection of 2,4-D by introducing a novel analytical method for its quantification. This method relies on the selective extraction of 2,4-D using MIPs and their subsequent direct analysis using ambient plasma mass spectrometry. During the synthesis, MIPs with various degrees of glycidol (GLY) functionalization were obtained. Experimental data showed that MIPs with no GLY functionalization displayed the highest adsorption capacity. Conversely, MIPs with 30% GLY functionalization exhibited the greatest selectivity for 2,4-D, rendering them valuable for extraction of 2,4-D even in the presence of other contaminants. Finally, the obtained MIPs were applied for quantification of 2,4-D in various water samples through direct analysis using a specially designed ambient plasma mass spectrometry setup. This approach improved the detection limits by 200-fold compared to pure solution analysis. The quantification of 2,4-D in river water samples yielded highly satisfactory recoveries, demonstrating the effective utility of the proposed analytical setup for real-life water sample analysis.

Molecularly Imprinted Polymers for Pharmaceutical Impurities: Design and Synthesis Methods

The safety of a medicinal product is determined by its pharmacological and toxicological profile, which depends not only on the active substance's toxicological properties, but also on the impurities it contains. Because impurities are a problem that must be considered to ensure the safety of a drug product, many studies have been conducted regarding the separation or purification of active pharmaceutical ingredients (APIs) and the determination of impurities in APIs and drug products. Several studies have applied molecularly imprinted polymers (MIPs) to separate impurities in active ingredients and as adsorbents in the sample preparation process. This review presents the design of MIPs and the methods used to synthesise MIPs to separate impurities in APIs and drug product samples, the application of MIPs to separate impurities, and a view of future studies involving MIPs to remove impurities from pharmaceutical products. Based on a comparison of the bulk and surface-imprinting polymerisation methods, the MIPs produced by the surface-imprinting polymerisation method have a higher adsorption capacity and faster adsorption kinetics than the MIPs produced by the bulk polymerisation method. However, the application of MIPs in the analysis of APIs and drug products are currently only related to organic compounds. Considering the advantages of MIPs to separate impurities, MIPs for other impurities still need to be developed, including multi-template MIPs for simultaneous separation of multiple impurities.

Highly Efficient Selective Extraction of Chlorpyrifos Residues from Apples by Magnetic Microporous Molecularly Imprinted Polymer Prepared by Reversible Addition-Fragmentation Chain Transfer Surface Polymerization

Chlorpyrifos, as a moderate toxic organophosphorus pesticide, is prone to lingering in the environment and cannot be monitored easily. In this study, a magnetic, microporous, molecularly imprinted polymer was synthesized by using the reversible addition-fragmentation chain transfer polymerization method. The synthesized materials were properly characterized in terms of morphology, selectivity, and sorption capacity and used as sorbents for magnetic solid phase extraction for the selective determination of chlorpyrifos in apple samples. Results showed that the magnetic microporous molecularly imprinted materials were rough and porous spheres at an average size of 5 nm. The materials were highly selective toward chlorpyrifos with a superior sorption capacity of 167.99 mg·g^-1 and were resistant to the interference of competitive pollutants. After optimization, the recoveries of chlorpyrifos reached 96.2-106.5%, and the detection limit was 0.028 μg·kg^-1 by HPLC. Based on these analytical validation results, the developed method could be effective at determining chlorpyrifos in apples.

Preparation and Adsorption Properties of Magnetic Molecularly Imprinted Polymers for Selective Recognition of 17β-Estradiol

In this paper, magnetic molecularly imprinted polymers (MMIPs) were fabricated on the surface of Fe3O4 by surface molecular imprinting technology, which can selectively adsorb 17β-estradiol (E2). The optimized experiments demonstrated that MMIPs possessed the best adsorption capacity when methanol was used as the solvent and MAA was used as the crosslinking agent, with a molar ratio of E2: MMA: EGDMA as 1:4:50. SEM, FTIR, and XRD were employed to investigate the morphologies of MMIPs and the results demonstrated that the MMIPs that can selectively adsorb E2 were successfully prepared on Fe3O4 particles. The adsorption experiments showed that 92.1% of E2 was adsorbed by the MMIPs, which is higher than the magnetic non-molecularly imprinted polymers (MNIPs). The Freundlich isotherm model was more suitable to describe the adsorption process of E2 by MMIPs. Meanwhile, MMIPs had a better recognition ability for E2 and its structural analogs such as estrone and estriol. The MMIPs still had good adsorption performance after methanol regeneration five times. The prepared MMIPs had the advantages of efficient adsorption ability and high reusability, so they can be applied for selective recognition and removal of E2.

Preparation of Molecularly Imprinted Polymer Microspheres for Selective Solid-Phase Extraction of Capecitabine in Urine Samples

Molecularly imprinted solid-phase extraction to treat biological samples has attracted considerable attention. Herein, molecularly imprinted polymer (MIP) microspheres with porous structures were prepared by a combined suspension-iniferter polymerization method using capecitabine (CAP) as a template molecule. This material was subsequently used as a solid-phase extraction agent to separate and enrich drug molecules in urine samples. UV analysis revealed that methacrylate (MAA) was an ideal functional monomer, and 1H Nuclear Magnetic Resonance (1H NMR), Ultraviolet (UV), and Fourier transform-infrared (FT-IR) spectroscopic analyses were used to study the interaction forces between MAA and CAP, demonstrating that hydrogen bonding was the primary interaction force. MIPs with outstanding selectivity were successfully prepared, and the analysis of their surface morphology and chemical structure revealed a spherical morphology with small holes distributed across a rough surface. This surface morphology significantly reduced the mass transfer resistance of template molecules, providing an ideal template recognition effect. Using the molecularly imprinted solid-phase extraction method, CAP and the structural analog cytidine (CYT) were pretreated in urine samples and quantified by HPLC. The results showed that CAP and CYT recoveries reached 97.2% and 39.8%, respectively, with a limit of detection of 10.0–50.0 µg·mL−1. This study provides a novel approach to drug molecule pretreatment that can be applied in drug separation and functional materials science fields.

Review on molecular imprinting technology and its application in pre-treatment and detection of marine organic pollutants

Molecular imprinting technology (MIT) has been considered as an attractive method to produce artificial receptors with the memory of size, shape and functional groups of the templates and has become an emerging technique with the potential in various fields due to recognitive specificity, high efficient selectivity and mechanical stability, which can effectively remove background interference and is suitable for the pre-treatment and analysis of trace level substances in complex matrix samples. Nearly 100 papers about the application of MIT in the detection of marine pollutants were found through Science Citation Index Expanded (SCIE). On this basis, combined with the application of MIT in other fields, the pre-treatment process of marine environmental samples was summarized and the potential of four types of different molecularly imprinted materials in the pre-treatment and detection of marine organic pollutants (including antibiotics, triazines, organic dyes, hormones and shellfish toxins) samples was evaluated, which provides the innovative configurations and progressive applications for the analysis of marine samples, and also highlights future trends and perspectives in the emerging research field.

Molecularly imprinted solid-phase extraction of Chikusetsu saponin IVa from Panacis majoris Rhizoma

As the main active component of Panacis majoris Rhizoma, Chikusetsu saponin IVa has the activity of anti-oxidation, anti-inflammatory pain, and so on. Obtaining high purity Chikusetsu saponin IVa by simple purification steps is a prerequisite for its deep development. In this paper, the separation and purification of Chikusetsu saponin IVa were studied by molecular imprinting technique. By ultraviolet and visible spectrophotometry and computer molecular simulation, it was concluded that water-soluble 3-(2-carboxyethyl)-1-vinylimidazolium bromide ionic liquid was the best functional monomer compared with acrylic acid and acrylamide. The molecularly imprinted polymers were prepared by precipitation polymerization at 60℃ with Chikusetsu saponin IVa as template molecule, 3-(2-carboxyethyl)-1-vinylimidazolium bromide as functional monomer, ethylene glycol dimethacrylate as cross-linker, 2, 2'-azobisisobutyronitrile as initiator, and ethanol as porogen. The properties of molecularly imprinted polymers were studied by scanning electron microscopy, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, nitrogen adsorption/desorption isotherm, and X-ray photoelectron spectroscopy. The maximum adsorption capacity was 171.33 mg/g, and the imprinting factor was 2.6. Finally, the polymers can be successfully used in the purification of Chikusetsu saponin IVa from Panacis majoris Rhizoma through a simple procedure, the content was significantly increased. The recoveries of the spiked samples for the CS-IVa ranged from 94.05 to 99.95% with relative standard deviation values lower than 2.67%. The results showed that the polymers demonstrated good adsorption capacity for Chikusetsu saponin IVa. Meanwhile, the polymers showed great stability and reusability during the application.

Analytical methods to analyze pesticides and herbicides

This paper reviews studies published in 2019, in the area of analytical techniques for determination of pesticides and herbicides. It should be noted that some of the reports summarized in this review are not directly related to but could potentially be used for water environment studies. Based on different methods, the literatures are organized into six sections, namely extraction methods, electrochemical techniques, spectrophotometric techniques, chemiluminescence and fluorescence methods, chromatographic and mass spectrometric techniques, and biochemical assays. PRACTITIONER POINTS: Totally 141 research articles have been summarized. The review is divided into six parts. Chromatographic and mass spectrometric techniques are the most widely used methods.