Selective determination of aromatic acids by new magnetic hydroxylated MWCNTs and MOFs based composite

Excellent performance separation of trypsin by novel ternary magnetic composite adsorbent based on betaine-urea- glycerol natural deep eutectic solvent modified MnFe2O4-MWCNTs

The effective trypsin purification methods should be established since trypsin plays a crucial role in biosome. In this work, a novel ternary magnetic composite adsorbent (MnFe₂O₄-MWCNTs@B-U-G) with the features of strong specific selectivity, good adsorption effect, simple and efficient separation process, no secondary pollution brought in was prepared by integrating the superior physicochemical properties of ternary based natural deep eutectic solvent, multi-walled carbon nanotubes and MnFe₂O₄. The property, composition and microtopography structure of MnFe₂O₄-MWCNTs@B-U-G were characterized in detail. Combined with magnetic solid-phase extraction, MnFe₂O₄-MWCNTs@B-U-G was utilized to adsorb trypsin. Response surface methodology experiment was prepared under Box-Behnken design to optimize the adsorption conditions and the results showed that the practical maximum adsorption capacity for trypsin was 1020.1 mg g^-1. Besides, the adsorption isotherms, adsorption kinetics, regeneration studies and method validation studies were investigated systematically to evaluate the established adsorption separation system. Mechanism exploration proved that electrostatic interaction, hydrogen bonding interaction and chelation interaction were the dominant forces for the high-performance adsorption of trypsin. The activity of trypsin after elution had been analyzed by UV-vis spectrophotometer and CD spectrometer with three methods, which illustrated that the enzyme activity, conformation and secondary structure of trypsin did not change significantly during the adsorption-desorption process. In addition, the proposed method was successful and practical applicability to isolation trypsin from crude bovine pancreas. As a result, due to the superiority of the MnFe₂O₄-MWCNTs@B-U-G, the proposed method not only exhibites high-performance adsorption of trypsin, but also provides a green and sustainable potential value in the adsorption of biomacromolecule.

Polyaniline spinel particles with ultrahigh-performance liquid chromatography tandem mass spectrometry for rapid vitamin B9 determination in rice

Rice is an important crop that provides energy and nutrients to humans, which undergoes the aging process, the quality decline is related to the exogenous storage conditions and the change of own enzyme activity. However, due to the complex composition of rice and serious matrix interference, the ageing identification of rice is still challenging. Hence, a novel spinel particles ZnFe₂O₄@PANI was designed and synthesized for adsorption and determination of vitamin B₉, which can be used to distinguish rice in different years and analyze the degree of aging. The ZnFe₂O₄@PANI showed large specific surface area and fast mass transfer rate with good linear correlation coefficient (R² = 0.9965), satisfactory recoveries (85.1%-99.9%) and relative standard deviations (RSD, 9.3%). Moreover, the π-π electron-donor-acceptor (EDA) and intermolecular hydrogen-bonding interactions of polyaniline coating provided selective adsorption on vitamin B₉. Adsorption thermodynamics study suggested that the adsorption reactions were spontaneous, endothermic and thermodynamically favorable. Finally, ZnFe₂O₄@PANI was used to evaluate vitamin B₉ in rice from different years, which laid a theoretical foundation for exploring the relationship between vitamin changes and the aging degree of the rice.

Effective dispersion of oxidized multi-walled carbon nanotubes using a water-soluble N,O-carboxymethyl chitosan via non-covalent interaction

Dispersible multi-walled carbon nanotubes (MWCNTs) in water have been widely applied in the nanotechnology field. This study reports a water-soluble N,O-carboxymethyl chitosan(N,O-CMCS) assisted individual dispersion of oxidized multi-walled carbon nanotubes (oMWCNTs) as a dispersant. First, the dispersing agent N,O-CMCS was successfully synthesized using the nucleophilic substitution of deacetylated chitosan with chloroacetic acid in an alkaline solution. It was further confirmed using Fourier transform infrared spectroscopy (FTIR). Second, after the treatment with the concentrated hydrochloric acid, the prepared oMWCNTs were dispersed in an aqueous solution of N,O-CMCS under ultrasonic vibrations. Finally, the dispersed aqueous solution was subjected to centrifugation to collect the supernatant of individually dispersed N,O-CMCS/oMWCNTs. In addition, transmission electron microscopy (TEM) further confirmed that the purity of oMWCNTs was improved after the acidification progress. Besides, the stability of the dispersion solution was evidenced by digital photos of oMWCNTs dispersed by N,O-CMCS before and after. Moreover, the UV-vis spectrum (the characteristic peak of dispersed oMWCNTs downshifted 13 nm) showed that the supernatant was enriched by the individual oMWCNTs. In particular, the analytical results of FTIR (the –NH₂ band of N,O-CMCS downshifted 7 cm⁻¹), resonance Raman spectroscopy (the I_D/I_G ratio of dispersed oMWCNTs only increased 0.14), and XRD identified the formation of a non-convalent interaction between N,O-CMCS and oMWCNTs. These findings reveal the dispersing nature of N,O-CMCS towards oMWCNTs in water media.

The stability of a dispersion solution was evidenced by images of oMWCNTs-dispersed by N,O-CMCS before (b) and after (a). UV-vis further showed that individual oMWCNTs were enriched via the non-covalent interaction between oMWCNTs and N,O-CMCS.

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

Plant hormones (PHs) are of significance in plant growth, as they regulate the various processes related to plant growth, development, and resistance. Sensitive and precise quantitative analysis of PHs is a bottleneck in plant science research. Currently, liquid chromatography-tandem mass spectrometry is used for the accurate and efficient detection of PHs. Sample pretreatment is an indispensable step in the chromatography-mass spectrometry analysis of PHs because it directly affects the sensitivity and accuracy of subsequent detection methods. Among various pretreatment methods for PHs, solid phase extraction (SPE) is the most widely used. Various new types of SPE, such as dispersive SPE, magnetic SPE, and solid phase microextraction, have been developed by modifying the extraction cartridge. The choice of adsorption material is the key factor in the abovementioned SPE methods, which has a decisive effect on the extraction, purification, and enrichment effects of the target substance in the sample pretreatment process. Carbon-based materials, including carbon nanotubes, graphene, carbon and nitrogen compounds, as well as organic frameworks, including metal organic frameworks and covalent organic materials, are suitable adsorption materials because of their designable structure, large specific surface area, and good stability. Molecularly imprinted polymers and supramolecular compounds show specific molecular recognition based on host-guest interactions, which can significantly improve the selectivity of sample pretreatment methods. In this paper, SPE-related technology and the abovementioned types of functionalized adsorption materials in the pretreatment of PHs prevalent in the past five years have been reviewed. The related development trends are also summarized.

Zeolitic imidazolate frameworks in analytical sample preparation

Zeolitic imidazolate frameworks are a class of metal-organic frameworks that are topologically isomorphic with zeolites. Zeolitic imidazolate frameworks are composed of tetrahedrally coordinated metal ions connected by imidazolate linkers and have a high porosity and chemical stability. Here, we summarize the progress made in the application of zeolitic imidazolate frameworks in sample preparation for analytical purposes. This review is focused on analytical methods based on liquid chromatography, gas chromatography, or capillary electrophoresis, where the use of zeolitic imidazolate frameworks has contributed to increasing the sensitivity and selectivity of the method. While bulk zeolitic imidazolate frameworks have been directly used in analytical sample preparation protocols, a variety of strategies for their magnetization or their incorporation into sorbent particles, monoliths, fibers, stir bars, or thin films, have been developed. These modifications have facilitated the handling and application of zeolitic imidazolate frameworks for a number of analytical sample treatments including magnetic solid-phase extraction, solid-phase microextraction, stir bar sorptive extraction, or thin film microextraction, among other techniques.