β-Cyclodextrin-grafted magnetic graphene oxide nanocomposites in ultrasound-assisted dispersive magnetic solid-phase extraction for simultaneous preconcentration of lead and cadmium ions

Research on Chemical Intermediates - This article presents an ultrasound-assisted dispersive magnetic solid-phase extraction method (USA-DMSPE) to preconcentration Cd(II) and Pb(II) simultaneously....     

Development of deep eutectic solvent–based microwave-assisted extraction combined with temperature controlled ionic liquid–based liquid phase microextraction for extraction of aflatoxins from cheese samples

In this study, for the first time, a deep eutectic solvent-based microwave-assisted extraction was combined with ionic liquid–based temperature controlled liquid phase microextraction for the extraction of several aflatoxins from cheese samples. Briefly, the analytes are extracted from cheese sample (3 g) into a mixture of 1.5 mL choline chloride:ethylene glycol deep eutectic solvent and 3.5 mL deionized water by exposing to microwave irradiations for 60 s at 180 W. The liquid phase was taken and mixed with 55 μL 1-hexyl-3-methylimidazolium hexafluorophosphate. By cooling the solution in the refrigerator centrifuge, a turbid state was obtained and the analytes were extracted into the ionic liquid droplets. The analytes were determined by high-performance liquid chromatography equipped with fluorescence detector. Low limits of detection (9–23 ng kg^–1) and quantification (30–77 ng kg^–1), high extraction recovery (66%–83%), acceptable enrichment factor (40–50), and good precision (relative standard deviations ≤ 5.2%) were obtained using the offered approach. These results reveal the high extraction capability of the method for determination of aflatoxins in the cheese samples. In this method, there was no need for organic solvents and it can be considered as green extraction method.     

Preparation of magnetic molecularly imprinted polymers based on a deep eutectic solvent as the functional monomer for specific recognition of lysozyme

A magnetized molecularly imprinted polymer (MIP) was prepared via a surface-imprinting technique. An allyl-based deep eutectic solvent was chosen as the functional monomer to obtain the polymer for specific recognition of lysozyme. It was deposited on silica-coated magnetite nanoparticles. The structure of the polymer was confirmed by X-ray diffraction, Fourier transform infrared spectrometry, transmission electron microscopy, thermogravimetric analysis and vibrating sample magnetometry. The maximum binding capacity of the imprinted polymer is found to be 108 mg·g^?1, which is higher than that of non-imprinted polymer. Compared to reference proteins such as cytochrome C, bovine hemoglobin and bovine serum albumin, the MIP shows favorable selectivity for lysozyme. Besides, the imprinted polymer can be further used to specifically recognize lysozyme from the protein mixture and chicken egg white. Reusability studies demonstrate that the polymer can be recycled four times without significant loss of adsorption capacity. The LOD of the method is 12.8 μg·mL^?1. The relative standard deviations (for n = 3) are 1.38% for precision and 2.76% for repeatability. Its facile synthesis, high adsorption performance and excellent selectivity to capture lysozyme make this polymer an attractive candidate to be applied in biomacromolecular purification.

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Graphical abstract Magnetic molecularly imprinted polymer (MIP) based on deep eutectic solvent as functional monomer was fabricated and applied for the specific recognition of lysozyme. The MIP exhibits high adsorption capacity and excellent selectivity for lysozyme.

     

Polyaniline/graphene oxide nanocomposite as a sorbent for extraction and determination of nicotine using headspace solid-phase microextraction and gas chromatography–flame ionization detector

A solid-phase microextraction fiber was prepared by polyaniline/graphene oxide nanocomposite as sorbent on the surface of a platinized stainless steel wire using electrospinning technique. The nanocomposite structure was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The polyaniline/graphene oxide nanocomposite fiber was used for the determination of nicotine from tobacco samples using headspace solid-phase microextraction method and gas chromatography–flame ionization detection. Influential experimental variables on the extraction efficiency of nicotine, such as extraction time and temperature, humidity and desorption conditions, were evaluated and optimized. Under the optimal experimental conditions? the limit of detection, linear dynamic range, intraday and inter-days precisions were found to be 0.01 μg g^?1, 0.05–700 µg g^?1 (R²?=?0.996), 6.9 and 8.1%, respectively. Comparison of the polyaniline/graphene oxide nanocomposite sorbent with polyaniline and commercial fibers shows longer durability, larger capacity and higher extraction efficiency. The polyaniline/graphene oxide nanocomposite fiber was successfully applied for the determination of nicotine in tobacco samples.     

A reversible fluorescent INHIBIT logic gate for determination of silver and iodide based on the use of graphene oxide and a silver–selective probe DNA

We describe a reversible fluorescent DNA–based INHIBIT logic gate for the determination of silver(I) and iodide ions using graphene oxide (GO) as a signal transducer and Ag(I) and iodide as mechanical activators. The basic performance, optimized conditions, sensitivity and selectivity of the logic gate were investigated and revealed that the method is highly sensitive and selective over potentially interfering ions. The limits of detection for Ag(I) and iodide are 10 nM and 50 nM, respectively. This logic gate was successfully applied to the determination of Ag(I) and iodide in (spiked) tap water and river water. It was also used for the determination of iodide in human urine samples with satisfactory results. Compared to other methods, this INHIBIT logic gate is simple in design and has small background interference.

A simple and reversible fluorescent DNA-based INHIBIT logic gate is designed by using graphene oxide as a signal transducer and silver ions and iodide as mechanical activators.

     

The graphene oxide/magnesium–aluminium bimetallic hydroxides composite used as solid-phase extractant for determination of monoaromatic hydrocarbons in wastewater

The graphene oxide (GO) and the magnesium–aluminium bimetallic hydroxides composite (GO/Mg-Al-LDH) was used as a solid-phase extractant for determination of toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene in wastewater by gas chromatography-mass spectrometry analytical method. When the amount of solid-phase extractant was 1.5 g, the extraction time was 6 min, and the elution with 2 mL of chloroform for 3 min, seven monoaromatic hydrocarbons (MAHCs) in 500 mL of water sample can be well extracted and separated. Under the optimised experimental conditions, the mass concentration of each component in the range of 0.01–5 ng/mL has a good linear relationship with the peak area, the coefficients of determination are all greater than 0.995. The relative standard deviation (n = 5) and the method detection limit range are 2.9–7.1% and 0.0005–0.005 ng/mL, respectively. The seven of MAHCs in Dongfengqu River and laboratory wastewater of Chengdu University of Technology can be effectively detected, the recovery rate and the relative standard deviation (n = 5) are 83.0–110.0% and 3.7–9.4%, respectively. For the first time, the GO/Mg-Al-LDH composite was used as a solid-phase extraction material, and seven MAHCs in water were successfully determined by GC-MS. The detection method is established with low detection limit and high reproducibility which can meet the measurement requirements of trace MAHCs in wastewater.     

Application of off-line pyrolysis with dynamic solid-phase microextraction to the GC–MS analysis of biomass pyrolysis products

Pyrolysis coupled with dynamic solid-phase micro extraction (Py-SPME) followed by GC–MS analysis was applied to the determination of volatile compounds evolved by a micro-scale off-line pyrolysis apparatus, in order to extend the information affordable with this type of analytical equipment. The Py-SPME method with a carboxen/PDMS fiber working in the retracted mode was tested on four biomass samples (switchgrass, sweet sorghum, corn stalk and poplar) for qualitative analysis of semi-volatile pyrolysis products and quantitative determination of main volatiles (C₁–C₄) pyrolysis products. The developed procedure allowed capturing and analysis of all GC analyzable compounds, without memory effects and with good peak resolution also for early GC-eluting compounds. Twelve main volatile pyrolysis products, including hydroxyacetaldehyde and acetic acid, were successfully quantified; in spite of the intrinsic variability introduced by dynamic SPME sampling, results were relatively accurate and consistent with literature data on bench pyrolysis reactors.     

Headspace solid-phase microextraction combined with GC×GC-TOFMS for the analysis of volatile compounds of Coptis species rhizomes

In this study, the investigation of the volatile compounds of dried rhizomes of Coptis chinensis Franch, C. deltoidea C. Y. Cheng et Hsiao, and C. teeta Wall was carried out to complete the chemical composition of these valuable natural products. Volatile profiles were established and compared after headspace solid-phase microextraction (HS-SPME) using a polydimethylsiloxane/divinylbenzene (PDMS/DVB, 65 μm) fibre coupled to comprehensive 2D gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS). Analyses were performed and compared on two column-phase combinations (non-polar/polar and polar/non-polar). The majority of the identified compounds eluted as well-separated (pure) components as a result of high-resolution capability of the GC×GC method, which significantly reduces co-elution. Therefore, this increases the likelihood that pure mass spectra can be obtained. More than 290 volatile and semi-volatile organic compounds were tentatively characterized by means of GC×GC in tandem with TOFMS detection. Improved result interpretations were obtained in terms of compound classification based on the organized structure of the peaks of structurally related compounds in the GC×GC contour plot. These compounds are distributed over the chemical groups of hydrocarbons, acids, alkenes, alkynes, aldehydes, ketones, alcohols, esters, furans, and terpenoids. Among all the chemical groups, terpenoids present the higher number of identified compounds (44), alkenes (41), and aldehydes and ketones (28). This study completed the volatile phytochemical analysis of the headspace composition of various Coptis species rhizomes, and should serve as a means to identify the difference between the rhizomes and may also be useful to confirm individual species based on their volatile chemical profile.     

A novel hierarchical nanobiocomposite of graphene oxide–magnetic chitosan grafted with mercapto as a solid phase extraction sorbent for the determination of mercury ions in environmental water samples

New mercapto-grafted graphene oxide–magnetic chitosan (GO–MC) has been developed as a novel biosorbent for the preconcentration and extraction of mercury ion from water samples. A facile and ecofriendly synthesis procedure was also developed for modification of GO–MC with 3-mercaptopropyltrimethoxysilane. The prepared nanocomposite material (mercapto/GO–MC) was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and energy-dispersive X-ray spectroscopy (EDX). The mercury analysis was performed by continuous-flow cold vapor atomic absorption spectrometry. The parameters affecting the extraction and preconcentration processes were carried out. The optimum conditions were found to be 60 mg of sorbent, pH of 6.5, 10 min for adsorption time, 3 mL of HCl (0.1 mol L⁻¹)/thiourea (2% w/v) as the eluent and 250 mL for breakthrough volume. An excellent linearity was achieved in the range of 0.12–80 ng mL⁻¹ (R² = 0.999) at a preconcentration factor of 80. The limit of detection and quantification were achieved as 0.06 ng mL⁻¹ and 0.12 ng mL⁻¹, respectively. A good repeatability was obtained with the relative standard deviation (RSD) of 4.7%. Furthermore, real water samples were analyzed and good recoveries were obtained from 95 to 100%.     

Conversion of xylose and xylan into furfural in biorenewable choline chloride–oxalic acid deep eutectic solvent with the addition of metal chloride

An environmentally benign processing approach for furfural production from xylose and xylan under very mild conditions(353–373 K) was developed with the addition of metal chlorides in ChCl–oxalic acid(a deep eutectic solvent(DES)) synthesized from cheap and renewable starting materials). ChCl–oxalic acid acted as both a Br?nsted acid catalyst and a reaction medium in this catalytic route. In addition, a biphasic system with methyl isobutyl ketone as an extracting reagent(DES/MIBK) to further increase furfural yield was also proposed. This processing approach for producing furfural eliminated the large energy consumption for high pressure saturated steam and the generation of acidic effluent, which was very difficult to handle. The whole catalytic system was more environmentally friendly compared with the commercial process for furfural production.     

Passerini three-component cascade reactions in deep eutectic solvent: an environmentally benign and rapid system for the synthesis of α-acyloxyamides

Research on Chemical Intermediates - A greener synthesis of α-acyloxyamides was achieved by one-pot three component cascade Passerini reactions in a deep eutectic solvent (DES). Reactions...     

Zinc oxide nanoparticles-based electrochemical sensor for the detection of nitrate ions in water with a low detection limit—a chemometric approach

We report for the first time a cyclic voltammetric nitrate sensor with a low detection limit based on the immobilization of zinc oxide nanoparticles on the surface of the platinum working electrode using chitosan membrane. Cyclic voltammetric data demonstrated that zinc oxide nanoparticles can electrochemically reduce nitrate ions to ammonium ions with high conductivity. In order to estimate electroanalytical parameters for each of the nitrate concentrations, Gaussian and Lorentzian curve fitting algorithms were performed on cyclic voltammetric data. Among them, the best analytical performance results were obtained with Gaussian calibration linear model. The zinc oxide modified platinum electrode showed a linear response to nitrate ions over a concentration range from 0.1 to 2.0 mM with a low detection limit and high sensitivity of 10 nM and 39.91 μA/cm² mM, respectively. The nitrate ion concentrations in drinking water samples were determined using Gaussian calibration linear model and the predicted, added nitrate ion concentration values showed good correlation.     

preconcentration and determination of amoxicillin and ceftriaxone in hospital sewage using vortex-assisted liquid-phase microextraction based on the solidification of the deep eutectic solvent followed by HPLC–UV

In the present study, a new method for extraction and preconcentration of amoxicillin and ceftriaxone was used in hospitalised sewage samples, called vortex-assisted liquid-phase microextraction based on the solidification of deep eutectic solvent. Samples were analysed by high-performance liquid chromatography–ultraviolet detection after preparation and extraction. In this method, the new deep eutectic solvent is used as the extraction solvent, which is obtained from the combination of 1-decyl-3-methylimidazolium chloride and n-butanoic acid. The important advantages of this novel extraction solvent include material stability, low density and good freezing point near room temperature. Under the optimum conditions, enrichment factors are in the range of 164–172. Repeatability and reproducibility of the method based on seven replicate measurements of 50.0 µg L^?1 of the target analytes in analysed samples were in the range of 2.1–3.5% and 3.8–5.2%, respectively. The limit of detections and linearity are in the range of 0.005–0.10 and 3–600 µg L^?1, respectively. The method was successfully applied for the determination of amoxicillin and ceftriaxone in the real sewage samples. The relative recoveries of sewage samples spiked with amoxicillin and ceftriaxone are 91–107%.     

Polyvinyl alcohol-modified graphene oxide as a support for bimetallic Pt–Pd electrocatalysts to enhance the efficiency of formic acid oxidation

The aim of this research was to study the efficiency of polyvinyl alcohol (PVA)-modified graphene oxide (GO) as a supporting material for catalysts that oxidize formic acid. The active metal catalysts (e.g., Pt and Pd) were electrodeposited on PVA/GO surfaces. The morphologies of the prepared catalysts were characterized by scanning electron microscopy and transmission electron microscopy, while their chemical compositions were identified by X-ray diffraction and X-ray photoelectron spectroscopy. The results show that compared with the other catalysts on GO, the prepared active PtPd alloy catalyst nanoparticles with 11.49–20.73 nm sizes were well dispersed on the PVA/GO surfaces. Electrochemical results indicate that the activities of the catalysts with PVA provided a higher current density than that of the catalysts without PVA. The bimetallic 3Pt3Pd/PVA/GO catalyst showed the greatest catalytic activity, stability, and CO oxidation when compared to those of other catalysts. The electronic, morphological, and structural properties promote the mass-charge transfer through the interaction. These results indicate that the PVA-modified GO provides a suitable site for active bimetallic catalyst surfaces, resulting in excellent formic acid oxidation and high CO elimination. The 3Pt3Pd/PVA/GO electrocatalyst is promising for enhancing formic acid oxidation.     

Choline chloride–ZnCl2: Recyclable and efficient deep eutectic solvent for the [2+3] cycloaddition reaction of organic nitriles with sodium azide

Herein we report first time choline chloride–zinc chloride based deep eutectic solvent is a green and efficient reaction medium for the [2+3] cycloaddition reaction of organic nitriles with sodium azide to afford the corresponding 5-substituted 1H-tetrazoles. The present method provides an environment-friendly route, short reaction times with excellent yields, safe process, and simple workup which make this method an attractive and useful contribution to the existing conventional processes for the synthesis of 5-substituted 1H-tetrazoles.     

Polydimethylsiloxane/graphene oxide/β-cyclodextrin sponge as a solid-phase extraction sorbent coupled with gas chromatography-mass spectrometry for rapid adsorption and sensitive determination of lavender essential oil

An adsorbent polydimethylsiloxane/graphene oxide/β-cyclodextrin sponge, which possessed the merits of high surface area, chemical stability, environment friendly, and excellent extraction capacity, was successfully fabricated. Based on the advantages, a novel microwave-assisted headspace solid-phase extraction method for lavender essential oil using polydimethylsiloxane/graphene oxide/β-cyclodextrin sponge as adsorbents was developed in this study. Various experimental parameters were studied. The optimal extraction conditions were as follows: 1 mg/mL as dopamine solution concentration, graphene oxide dosages of 30 mg, microwave power of 700 W, microwave irradiation time of 10 min, and desorption solvent of n-hexane. Under the optimal extraction condition, linearities ranging from 10 to 800 ng were achieved for six representative compounds with a correlation coefficients value of >0.99. The intra-day and inter-day precisions were in the ranges of 0.40–1.56 and 0.67–2.56%, respectively. Finally, the proposed technique was applied to analyze essential oil constituents in 14 samples of three lavender varieties, and 48 compounds were identified. Lavender varieties were distinguished using principal component analysis and partial least squares discriminant analysis. The results showed that the method developed in this study is a novel, simple, and sensitive method for the determination of essential oil in complex plant samples.     

Matrix solid-phase dispersion coupled with magnetic ionic liquid dispersive liquid–liquid microextraction for the determination of triazine herbicides in oilseeds

A novel method was developed for the determination of six triazine herbicides from oilseeds by matrix solid-phase dispersion combined with magnetic ionic liquid dispersive liquid–liquid microextraction (MSPD-MIL-DLLME), followed by ultrafast liquid chromatography with ultraviolet detection (UFLC-UV). The MIL, 1-butyl-3-methylimidazolium tetrachloroferrate ([C₄mim][FeCl₄]), was used as the microextraction solvent to simplify the extraction procedure by magnetic separation. The effects of several important experimental parameters, including type of dispersant, ratio of sample to dispersant, type and volume of collected elution solvent, type and volume of MIL, were investigated. Using the present method, UFLC-UV gave the limits of detection (LODs) of 1.20–2.72 ng g⁻¹ and the limits of quantification (LOQs) of 3.99–9.06 ng g⁻¹ for triazine herbicides. The recoveries were ranged from 82.9 to 113.7% and the relative standard deviations (RSDs) were equal or lower than 7.7%. The present method is easy-to-use and effective for extraction of triazine herbicides from oilseeds and shows the potentials of practical applications in the treatment of the fatty solid samples.     

New functionalization of graphene oxide with N2O2 ligand for efficient loading of Cu nanostructures as a heterogeneous nanocatalyst for the synthesis of β-hydroxy-1,2,3-triazoles

A new and heterogeneous copper complex immobilized on graphene oxide (GO) was prepared. This was achieved through organic functionalization of GO using 1,8-diamino-3,6-dioxaoctane (DADO) and then inorganic coordination of copper on the edges and basal plane of the functionalized GO (GO-DADO-Cu), which was reduced to Cu(0). The chemical structure of the prepared nanocatalyst was analyzed using various techniques. Most of the analyses confirmed the successful anchoring of copper and organic ligand on the GO surface. Moreover, the synthesized nanocatalyst has shown high catalytic activity in the synthesis of β-hydroxy-1,2,3-triazole derivatives under mild reaction conditions (water and room temperature) resulting in good to excellent yields.