Qiong Jia

Studies on synergistic solvent extraction of rare earth elements from nitrate medium by mixtures of 8-hydroxyquinoline with Cyanex 301 or Cyanex 302

Synergistic solvent extraction of rare earth elements (REEs) from nitrate medium was investigated with mixtures of 8-hydroxyquinoline (HQ) and acidic organophosphorus extractants, bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex 301) and bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex 302). The extraction behavior of Cyanex 301/Cyanex 302 and their binary mixtures with HQ towards several lanthanoids (La, Nd, Sm, Tb, Ho, Tm) and yttrium (Y) was investigated. The separation ability of REEs was studied according to the various extraction effects. The extraction mechanisms for yttrium were studied with the methods of slope analysis and constant moles in the synergistic systems. The extracted compounds, the equilibrium constants, and thermodynamic functions were also determined.

Preparation and evaluation of ionic liquid-calixarene solid-phase microextraction fibres for the determination of triazines in fruit and vegetable samples

A new ionic liquid (IL)-calixarene coated solid-phase microextraction (SPME) fibre has been synthesized on the surface of quartz fibre by the sol-gel method. The coated fibre has been coupled with gas chromatography-flame ionisation detector (GC-FID) for the determination of triazines in fruit and vegetable samples. The operation parameters including sample volume, extraction time, extraction temperature, desorption time, and sample pH have been investigated and optimised. Under the optimum conditions, the limits of detection of atrazine, simazine, ametryn, and cyanazine based on three times of standard deviations of blank by seven replications are 3.3, 4.4, 8.8, and 13.0 μg kg(-1), respectively. The intra-day and inter-day relative standard deviations are less than 7.2% and 9.9%. The proposed method has been successfully applied to the determination of the four triazines in fruit and vegetable samples and the accuracy is assessed through recovery experiments.

Polydopamine-based immobilization of a hydrazone covalent organic framework for headspace solid-phase microextraction of pyrethroids in vegetables and fruits

We designed a novel hydrazone covalent organic framework (COF) and developed a polydopamine (PDA) method to immobilize COF on a stainless steel fiber for headspace solid-phase microextraction (HS-SPME). A series of characterization studies was performed to validate the structure and property of the prepared fiber. The COF-PDA fiber was applied for the extraction of pyrethroids coupled with gas chromatography equipped with an electron capture detector (GC-ECD). Under the optimum experimental conditions, high enhancement factors of 307-2327 were achieved, indicating that the hydrazone COF possessed good extraction efficiency for pyrethroids. The detection limits ranged from 0.11 to 0.23μgkg(-1) with relative standard deviations varying in the range of 3.6-9.2% (intra-batch) and 6.9-12.1% (inter-batch), respectively. The developed method was applied to the determination of pyrethroids in fruit and vegetable samples and the accuracy was assessed through recovery experiments.

Preparation and characterization of magnetic nanoparticles for the on-line determination of gold, palladium, and platinum in mine samples based on flow injection micro-column preconcentration coupled with graphite furnace atomic absorption spectrometry

A simple and highly selective procedure for on-line determination of trace levels of Au, Pd, and Pt in mine samples has been developed using flow injection-column adsorption preconcentration coupled with graphite furnace atomic absorption spectrophotometry (FI-column-GFAAS). The precious metals were adsorbed on the as-synthesized magnetic nanoparticles functionalized with 4-aminobenzo-15-crown-5-ether packed into a micro-column and then eluted with 2% thiourea + 0.1 mol L(-1) HCl solution prior to the determination by GFAAS. The properties of the magnetic adsorbents were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Various experimental parameters affecting the preconcentration of Au, Pd, and Pt were investigated and optimized. Under the optimal experimental conditions, the detection limits of the developed technique were 0.16 ng mL(-1) for Au, 0.28 ng mL(-1) for Pd, and 1.01 ng mL(-1) for Pt, with enrichment factors of 24.3, 13.9, and 17.8, respectively. Precisions, evaluated as repeatability of results, were 1.1%, 3.9%, and 4.4% respectively for Au, Pd, and Pt. The developed method was validated by the analysis of Au, Pd, and Pt in certified reference materials and mine samples with satisfactory results.

Preconcentration procedures for the determination of chromium using atomic spectrometric techniques: A review

Chromium is one of the regulated toxic metals in the environment. Naturally, this element exists mainly in two oxidation: Cr(III) and Cr(VI). In general, Cr(VI) is more toxic than Cr(III). Cr(VI) affects human physiology, accumulates in the food chain and causes severe health problems ranging from simple skin irritation to lung carcinoma. Hence, the determination of chromium traces as well as its speciation in environmental samples is a very important task. In recent years, several preconcentration methods such as coprecipitation, liquid-liquid extraction, dispersive liquid-liquid microextraction, cloud point extraction, and solid phase extraction have been developed and widely used. The aim of this study is to review the recent literature (mainly last 5 years) on the preconcentration technologies those have been used in chromium removal before the determination step by atomic spectrometric techniques. Their advantages and limitations in application are also evaluated.

Fabrication of cross-linked hydrazone covalent organic frameworks by click chemistry and application to solid phase microextraction

Covalent organic frameworks (COFs) are an emerging class of porous organic frameworks with diverse promising applications. Herein, we presented the first example of cross-linked hydrazone COFs (cross-linked COFs) coating via thiol-ene click chemistry for solid phase microextraction (SPME). Strong covalent bonds and interlayer of the prepared networks ensured the adsorption capacity and durability of the novel SPME fiber. π-π conjugated structure existed because of abundant phenyl rings and -C=N groups in the cross-lined COFs. A series of characterizations indicated that the cross-linked COFs possessed large surface areas, high porosities and stabilities as well as hydrophobicities. The fiber was applied to SPME of pesticide residues coupled with gas chromatography with an electron capture detector (GC-ECD). Under the optimum experimental conditions, enhancement factors in the range of 2190-10,998 were obtained, illustrating that the cross-linked COFs possessed remarkable preconcentration ability. The low detection limits of 0.0003-0.0023ngkg-1 were achieved with relative standard deviations (RSDs) in the range of 3.4-7.6% (intra-batch) and 5.7-11.6% (inter-batch), respectively. Recovery values in the range of 78.2-107.0% were obtained when the SPME-GC method was applied to the analysis of pesticides in cucumber samples.

A graphene oxide functionalized with 3-aminophenylboronic acid for the selective enrichment of nucleosides, and their separation by capillary electrophoresis

AbstractWe show that graphene oxide functionalized with 3-aminophenylboronic acid represents a useful new adsorbent for the selective enrichment of the nucleosides, adenosine, guanosine, uridine, and inosine, which then were quantified by capillary electrophoresis. The analytes were separated within 10xa0min using a borate buffer of pHxa09.3 (containing sodium dodecyl sulfate) at an operating voltage of 25xa0kV, a temperature of 20xa0°C, a sample injection time of 5xa0s, and with UV detection at 254xa0nm. The effects of sample pH, sample flow rate, eluent type, and eluent flow rate were optimized. Under the optimized conditions, the enrichment factor was determined to be 10. A linear relationship was obtained over the 0.1 to 100xa0μgxa0mL−1 concentration range, with regression coefficients of >0.9991. The intra-day and inter-day relative standard deviations of this method were in the range of 3.1–5.0xa0% and 4.8–7.5xa0%, respectively. The method was applied to the determination of the nucleosides in (spiked) traditional Chinese medicine injection samples, and recoveries ranged from 70.8 to 106.7xa0%.n FigureGraphene oxide functionalized with 3-aminophenylboronic acid was prepared for the enrichment of nucleosides combined with capillary electrophoresis. After optimizing various experimental parameters, the method was successfully applied to the determination of nucleosides in traditional Chinese medicine injection samples.

A novel organic-inorganic hybrid monolithic column prepared in-situ in a microchip and its application for the determination of 2-amino-4-chlorophenol in chlorzoxazone tablets

γ-Alumina nanoparticles (γ-Al2O3) were introduced to the conventional poly(methacrylic acid-co-ethylene glycol dimethacrylate) (MAA-co-EGDMA) monolith to prepare a novel organic-inorganic hybrid monolith, poly(MAA-co-EGDMA)-Al2O3 monolith. The polymerization was induced in-situ with UV irradiation in an ultraviolet transparent polymethyl methacrylate (PMMA) microfluidic chip. The monolith-based solid phase microextraction system was used for the on-line determination of 2-amino-4-chlorophenol (ACP) in chlorzoxazone tablets coupled with an optical fiber spectrophotometer. Several parameters affecting the adsorption/desorption, including sample pH value, sample flow rate, sampling time, eluent flow rate, and eluting time, were investigated in detail. Under the optimized conditions, limit of detection (LOD) and limit of quantification (LOQ) of the method were calculated to be 2.8 and 9.1 µg L(-1), respectively, with the relative standard deviation (RSD) of 3.1%.

Synthesis of graphene oxide functionalized surface-imprinted polymer for the preconcentration of tetracycline antibiotics

In this work, we synthesized graphene oxide functionalized a surface-imprinted polymer based on the self-polymerization of dopamine to generate the imprinted cavity. Using minocycline as the template molecule, effects of experimental conditions in the imprinting procedure such as γ-MAPS@GO percentage, template concentration, and self-polymerization time of dopamine on the selectivity and performance of the prepared molecularly imprinted polymers were investigated. The characteristics of the prepared surface-imprinted polymer were determined by scanning electron microscope, transmission electron microscope, energy dispersive spectroscopy, Fourier-transformed infrared spectra, X-ray photoelectron spectroscopy, thermal gravimetric analysis, atomic force microscope, and water contact angle. The prepared graphene oxide functionalized surface-imprinted polymer showed good recognition capacity and enrichment performance for tetracycline antibiotics and was successfully applied to the detection of the target analytes in milk samples.

Preconcentration and determination of pesticides with graphene-modified polymer monolith combined with high performance liquid chromatography

In this study, a graphene-modified poly(butyl methacrylate–ethylene dimethacrylate) monolithic column was successfully utilized for purification and enrichment of four pesticides (fludioxonil, cyprodinil, flusilazole, and triflumizole) in fruit and vegetable samples. Several experimental parameters affecting the extraction efficiency were investigated, such as sample pH, sample flow rate, sample volume, salt concentration, eluent type, and eluent flow rate. Combined with HPLC analysis under the optimized conditions, good linearities were obtained for all targets with R2 values greater than 0.9965. The limits of detection (S/N = 3) for four pesticides were found to be in the range of 0.93–3.0 μg kg−1. The intra-day and inter-day relative standard deviations, ranging from 3.4% to 6.2%, were within an acceptable scope. Compared with direct HPLC analysis and preconcentration with unmodified poly(butyl methacrylate–ethylene dimethacrylate) monolith, the incorporation of graphene into the monolith increased the enrichment capacity for the analytes. The developed method was successfully applied to the determination of pesticides in fruit and vegetable samples (apple, grape, orange, tomato, cucumber, rape). The recoveries of four pesticides at different spiked levels in the samples were in the range of 70.2–95.0% with the relative standard deviations less than 6.4%.