Monodispersed mesoporous SiO2@metal-organic framework (MSN@MIL-101(Fe)) composites as sorbent for extraction and preconcentration of phytohormones prior to HPLC-DAD analysis

Chemical bonding of cross-linked glutaraldehyde/chitosan on the surface of a titanium wire to prepare a robust biocompatible SPME fiber for analysis of phytohormones in plants

A robust biocompatible solid-phase microextraction (SPME) fiber, so-called Ti/APTS/GA/CS, was prepared by chemical bonding of cross-linked glutaraldehyde-chitosan to the surface of a titanium wire using APTS. The fiber was applied for sampling of phytohormones in plant tissues, followed by HPLC-UV analysis. The structure and morphology of the fiber coating was investigated by FT-IR, SEM, EDX, XRD, and TGA techniques. A Box-Behnken design was implemented to optimize the experimental variables. The calibration graphs were linear over a wide linear range (0.5-200 μg L-1) with LODs over the range of 0.01-0.06 μg L-1. The intra-day and inter-day precisions were found to be 1.3-6.3% and 4.3-7.3%, respectively. The matrix effect values ranged from 86.5% to 111.7%, indicating that the complex sample matrices had an insignificant effect on the determination of phytohormones. The fiber was successfully employed for the direct-immersion SPME (DI-SPME-HPLC) analysis of the phytohormones in cucumber, tomato, date palm, and calendula samples.

Preparation of metal-organic framework @molecularly imprinted polymers for extracting N-nitrosamines in salted vegetables

In this paper, the novel metal-organic framework @molecularly imprinted polymers were prepared and applied in extracting N-nitrosamines from salted vegetables. The imprinted polymers were coated on the surface of MIL-101 using multi-dummy template molecules (5-nonanol, benzhydrol and N-formylpyrrolidine). The characterization and adsorbing experiments showed that the hybrid imprinted polymers presented spherical particles with typically core-shell structure, and exhibited high adsorption capacity (maximum capacity: 46.85 mg/g) and fast equilibrium rate (only 5 min) for N-nitrosamines. Various parameters (sample loading solvent, pH, washing solvent, elution solvent and elution volume) affecting solid-phase extraction were optimized. Under the optimum conditions, the solid-phase extraction process based on the hybrid polymers combined with high performance liquid chromatography-ultraviolet detection method was established and applied to analyze N-nitrosamines in different salted vegetables. The results showed that the developed method produced the linear relationship between the peak areas versus the N-nitrosamines concentrations of 0.2-10 µg/g with limit of detections from 20.6 to 76.1 ng/g. The spiked recovery of N-nitrosamines in the salted vegetable samples was in the range of 66-100.5 % with relative standard deviation from 0.1 to 3.4 %. Those results demonstrated that the established method was sensitive and efficient for directly enriching and analyzing trace N-nitrosamines in salted vegetables.

Synthesis of Metal–Organic Frameworks Quantum Dots Composites as Sensors for Endocrine-Disrupting Chemicals

Hazardous chemical compounds such as endocrine-disrupting chemicals (EDCs) are widespread and part of the materials we use daily. Among these compounds, bisphenol A (BPA) is the most common endocrine-disrupting chemical and is prevalent due to the chemical raw materials used to manufacture thermoplastic polymers, rigid foams, and industrial coatings. General exposure to endocrine-disrupting chemicals constitutes a serious health hazard, especially to reproductive systems, and can lead to transgenerational diseases in adults due to exposure to these chemicals over several years. Thus, it is necessary to develop sensors for early detection of endocrine-disrupting chemicals. In recent years, the use of metal–organic frameworks (MOFs) as sensors for EDCs has been explored due to their distinctive characteristics, such as wide surface area, outstanding chemical fastness, structural tuneability, gas storage, molecular separation, proton conductivity, and catalyst activity, among others which can be modified to sense hazardous environmental pollutants such as EDCs. In order to improve the versatility of MOFs as sensors, semiconductor quantum dots have been introduced into the MOF pores to form metal–organic frameworks/quantum dots composites. These composites possess a large optical absorption coefficient, low toxicity, direct bandgap, formidable sensing capacity, high resistance to change under light and tunable visual qualities by varying the size and compositions, which make them useful for applications as sensors for probing of dangerous and risky environmental contaminants such as EDCs and more. In this review, we explore various synthetic strategies of (MOFs), quantum dots (QDs), and metal–organic framework quantum dots composites (MOFs@QDs) as efficient compounds for the sensing of ecological pollutants, contaminants, and toxicants such as EDCs. We also summarize various compounds or materials used in the detection of BPA as well as the sensing ability and capability of MOFs, QDs, and MOFs@QDs composites that can be used as sensors for EDCs and BPA.

Understanding the Working Mechanism of the NovelHKUST-1@BPS Composite Materials as Stationary Phases for Liquid Chromatography

Composite materials have been used based on coordination polymers or microporous metal-organic frameworks (MOFs) combined with mesoporous matrices for adsorption-related techniques, which enable outflanking some adverse phenomena manifested during pristine components operation and enhance the performance and selectivity of the resulting materials. In this work, for the first time, the novel HKUST-1@BPS composites synthesized by the microwave-assisted (MW) technique starting from microporous HKUST-1 (Cu₃(btc)₂) MOF and biporous silica matrix (BPS) with bimodal mesopore size distribution were comparatively studied as materials for liquid-phase adsorption techniques utilizing the high-performance liquid chromatography (HPLC) method and benzene as a model adsorbate. It was established that the studied HKUST-1@BPS composites can function as stationary phases for HPLC, unlike the pristine HKUST-1 and bare BPS materials, due to the synergetic effect of both components based on the preliminary enhanced adsorbate mass transfer throughout the silica mesopores and, subsequently, its penetrating into HKUST-1 micropores. The suggested mechanism involves the initial deactivation of open metal Cu²⁺ sites in the HKUST-1 framework structure by isopropanol molecules upon adding this polar component into the mobile phase in the region of the isopropanol concentration of 0.0 to 0.2 vol.%. Thereafter, at the medium range of varying the isopropanol concentration in the eluent of 0.2 to 0.3 vol.%, there is an expansion of the previously inaccessible adsorption centers in the HKUST-1@BPS composites. Subsequently, while further increasing the isopropanol volume fraction in the eluent in the region of 0.3 to 5.0 vol.%, the observed behavior of the studied chromatographic systems is similar to the quasi-normal-phase HPLC pattern. According to the obtained thermodynamic data, benzene adsorption into HKUST-1 micropores from solutions with a vol.% of isopropanol in the range of 0.4 to 5.0 follows the unique entropy-driven mechanism previously described for the MIL-53(Al) framework. It was found that HKUST-1 loading in the composites and their preparation conditions have pronounced effects on their physicochemical properties and adsorption performance, including the adsorption mechanism.

Fabrication of stable multivariate metal-organic frameworks with excellent adsorption performance toward bisphenols from environmental samples

As a type of environmental endocrine disrupting chemicals, bisphenols (BPs) have a certain embryonic toxicity and teratogenicity, which can significantly increase the risks of breast cancer, prostate cancer, leukemia and other cancers. In this work, stable multivariate metal-organic frameworks (UiO-66-NH₂/TCPP_x) were synthesized via in situ one-pot method and used as miniaturized dispersive solid-phase extraction (dμSPE) sorbents for extraction of trace BPs from environmental samples. The phase purity, crystal morphology and physical properties of UiO-66-NH₂/TCPP_x samples were varied by adjusting the mass ratio of TCPP. The extraction performance of UiO-66-NH₂/TCPP_x samples were investigated and UiO-66-NH₂/TCPP_1.0 exhibited the highest adsorption efficiency. Besides, UiO-66-NH₂/TCPP_1.0 possessed excellent recycling stability for the adsorption and desorption of BPs more than 20 cycles. The experimental parameters including amount of adsorbent, adsorption time, sample solution pH, temperature, desorption time and desorption solvents which affecting the efficiency of dμSPE were studied, respectively. Good linearity (R² > 0.9992) in range of 0.1-200 ng mL^-1 was obtained. The detection limits (S/N = 3) and quantification limits (S/N = 10) were achieved at 0.03-0.08 ng mL^-1 and 0.1-0.5 ng mL^-1, respectively. The relative standard deviations (RSDs) of intra-day and inter-day ranged from 2.5 to 5.5% and 1.1-6.8%. Enrichment factors were calculated in the range of 303-338. The obtained recoveries of bisphenol F (BPF), bisphenol A (BPA), bisphenol B (BPB) and bisphenol AF (BPAF) were 81.26-91.03% (RSDs = 0.96-6.47%), 82.2-97.27% (RSDs = 0.45-6.15%), 87.56-97.26% (RSDs = 1.1-6.22%) and 82.2-100.8% (RSDs = 0.46-4.07%). The UiO-66-NH₂/TCPP_1.0 can be employed as potential dμSPE sorbents for the enrichment of trace BPs in the environmental samples.

[Novel adsorption material for solid phase extraction in sample pretreatment of plant hormones]

植物激素在植物生长过程中具有重要作用,调节植物生长、发育及抗逆的各个过程。植物激素超微精准定量分析一直是植物生理学研究的瓶颈问题。植物激素的准确、高效检测目前大多是基于液相色谱-串联质谱联用技术。样品前处理是植物激素色谱-质谱分析中必不可少的一个步骤,直接影响后续检测方法的灵敏度和准确性。在植物激素各种前处理方法中,固相萃取(SPE)技术应用非常广泛。在萃取小柱基础上发展了多种新形式(分散固相萃取、磁性固相萃取、固相微萃取等,称之为SPE相关方法)。在上述SPE相关方法中,吸附材料的选择均是关键因素,决定了样品前处理过程的目标物提取、净化和富集效果。碳基材料(包括碳纳米管、石墨烯、碳氮化合物等)和有机骨架材料(包括金属有机骨架、共价有机材料)拥有结构可设计、比表面积大、稳定性良好等特性,非常适合作为吸附材料。分子印迹聚合物和超分子化合物依靠主-客体特异性分子识别作用,能显著提高样品前处理方法的选择性。本文重点针对植物激素样品前处理中的SPE技术,综述了近5年来上述几类功能化吸附材料的最新应用进展,并对其发展趋势进行展望。

MIL-101(Fe)-derived magnetic porous carbon as sorbent for stir bar sorptive-dispersive microextraction of sulfonamides

Using MIL-101(Fe) as the source of carbon and Fe, a magnetic porous carbon (MPC) material with Fe₃C nanoparticles encapsulated in porous carbon was prepared through one-pot pyrolysis under N₂ atmosphere. With MPC as adsorption material, a stir bar sorptive-dispersive microextraction (SBSDME) method was proposed to extract and preconcentrate sulfonamides (SAs) prior to HPLC-DAD determination. To investigate their extraction ability, different MPC materials were prepared under different carbonization temperatures (600, 700, 800, 900, and 1000 °C). The material prepared under 900 °C (MPC-900) exhibited the highest extraction ability for SAs. The as-prepared MPC materials were also characterized by Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, zeta potential, and other techniques. The main parameters that affect extraction were systematically studied. Under optimal conditions, favorable linearity (R² ≥ 0.9938) and detection limits (0.02-0.04 ng mL^-1) of sulfonamides were obtained. The average recoveries for spiked milk and lake water samples ranged from 76.9 to 109% and from 75.4 to 118% with RSDs of 3.10-9.63% and 1.71-11.3%, respectively. Sulfameter and sulfisoxazole were detected in milk sample. Sulfisoxazole was detected in the lake water sample. The MPC-900 material demonstrated excellent reusability. It can be reused 24 times with peak areas having no obvious decline. The method can be applied to extract ultra-trace compounds in complex sample matrices. Schematic presentation of a stir bar sorptive-dispersive microextraction (SBSDME) by using magnetic porous carbon (MPC) composites as sorbent combined with high-performance liquid chromatography for sensitive analysis of sulfonamides in milk and lake water samples.

ZrO2 Nanoparticles and Poly(diallyldimethylammonium chloride)-Doped Graphene Oxide Aerogel-Coated Stainless-Steel Mesh for the Effective Adsorption of Organophosphorus Pesticides

A novel sorbent based on the ZrO₂ nanoparticles and poly(diallyldimethylammonium chloride)-modified graphene oxide aerogel-grafted stainless steel mesh (ZrO₂/PDDA-GOA-SSM) was used for the extraction and detection of organophosphorus pesticides (OPPs). Firstly, the PDDA and GO composite was grafted onto the surface of SSM and then freeze-dried to obtain the aerogel, which efficiently reduced the accumulation of graphene nanosheets. It integrated the advanced properties of GOA with a thin coating and the three-dimensional structural geometry of SSM. The modification of ZrO₂ nanoparticles brought a selective adsorption for OPPs due to the combination of the phosphate group as a Lewis base and ZrO₂ nanoparticles with the Lewis acid site. The ZrO₂/PDDA-GOA-SSM was packed into the solid-phase extraction (SPE) cartridge to extract OPPs. According to the investigation of different factors, the extraction recovery was mainly affected by the hydrophilic-hydrophobic properties of analytes. Effective extraction and elution parameters such as sample volume, sample pH, rate of sample loading, eluent, and eluent volume, were also investigated and discussed. Under the optimal conditions, the linearity of phoxim and fenitrothion was in the range of 1.0-200 μg L^-1, and the linearity of temephos was in the range of 2.5-200 μg L^-1. The limits of detection were ranged from 0.2 to 1.0 μg L^-1. This established method was successfully applied to detect OPPs in two vegetables. There was no OPP detected in real samples, and results showed that the matrix effects were in the range of 46.5%-90.1%. This indicates that the ZrO₂/PDDA-GOA-SSM-SPE-HPLC method could effectively extract and detect OPPs in vegetables.

Recent advances in micro- and nanomaterial-based adsorbents for pipette-tip solid-phase extraction

There are a lot of review papers of sample pretreatment, but the comprehensive review on pipette-tip solid-phase extraction (PT-SPE) is lacking. This review (133 references) is mainly devoted to the development of different types of micro- and nanosorbent-based PT-SPE, including silica materials, carbon materials, organic polymers, molecularly imprinted polymers, and metal-organic frameworks. Each section mainly introduces and discusses the preparation methods, advantages and limitations of adsorbents, and their applications to environmental, biological, and food samples. This review also demonstrates the advantages of PT-SPE like convenience, speed, less organic solvent, and low cost. Finally, the future application and development trend of PT-SPE are prospected.