Characterization of particulate products for aging of ethylbenzene secondary organic aerosol in the presence of ammonium sulfate seed aerosol.

Aging of secondary organic aerosol (SOA) particles formed from OH- initiated oxidation of ethylbenzene in the presence of high mass (100-300µg/m(3)) concentrations of (NH4)2SO4 seed aerosol was investigated in a home-made smog chamber in this study. The chemical composition of aged ethylbenzene SOA particles was measured using an aerosol laser time-of-flight mass spectrometer (ALTOFMS) coupled with a Fuzzy C-Means (FCM) clustering algorithm. Experimental results showed that nitrophenol, ethyl-nitrophenol, 2,4-dinitrophenol, methyl glyoxylic acid, 5-ethyl-6-oxo-2,4-hexadienoic acid, 2-ethyl-2,4-hexadiendioic acid, 2,3-dihydroxy-5-ethyl-6-oxo-4-hexenoic acid, 1H-imidazole, hydrated N-glyoxal substituted 1H-imidazole, hydrated glyoxal dimer substituted imidazole, 1H-imidazole-2-carbaldehyde, N-glyoxal substituted hydrated 1H-imidazole-2-carbaldehyde and high-molecular-weight (HMW) components were the predominant products in the aged particles. Compared to the previous aromatic SOA aging studies, imidazole compounds, which can absorb solar radiation effectively, were newly detected in aged ethylbenzene SOA in the presence of high concentrations of (NH4)2SO4 seed aerosol. These findings provide new information for discussing aromatic SOA aging mechanisms.

[Research progress in the application of magnetic solid phase extraction based on carbon based magnetic materials in food analysis].

Trace toxic substances in food pose a serious threat to human health, and need to be detected and analyzed to ensure food safety. However, there are many kinds of toxic substances in food, with small amounts and complex matrices, making it necessary to select an appropriate sample pretreatment technology for extraction and purification. There are some disadvantages to sample pretreatment methods such as solid phase extraction and liquid-liquid extraction, in terms of poor selectivity, significant influence of matrix interference, large sample requirement, long extraction time, use of a large amount of harmful organic solvents, and cumbersome and time-consuming operation. Magnetic solid phase extraction (MSPE) combines the advantages of magnetic separation and traditional SPE technology, avoids time-consuming column loading, and can extract the target analyte efficiently. Because of its advantages, in that it has simple operation, is time-saving and fast, requires no centrifugal filtration, and is environmentally friendly, it is considered an efficient sample pretreatment technology and applied in food analysis. The adsorption capacity and selectivity of the magnetic adsorbent used in MSPE are the key factors affecting the extraction efficiency and selectivity of MSPE, and play a key role in the accuracy of the established method. Carbon-based magnetic materials are a type of new functional magnetic materials prepared by the co-precipitation of carbon-based materials (carbon nanotubes, graphene, metal-organic framework-derived carbon, or activated carbon) and magnetic materials. In order to endow carbon-based magnetic materials with the advantages of both, carbon materials and magnetic materials, while also reflecting the advantages of high specific surface area, good stability, low cost, environmental friendliness, excellent physical and chemical properties, high porosity, and high adsorption capacity, proper functional modification is needed. Carbon-based magnetic materials modified by functionalization can efficiently enrich organic and inorganic analytes with different properties, and have seen significant progress in environmental analysis, biological detection, pollution control, and other fields. In recent years, MSPE technology based on carbon-based magnetic materials has been gradually applied in food analysis and pretreatment, but its use is still in infancy and holds immense application potential. Reference to more than 50 papers published in SCI and Chinese core journals over the past four years reveals that carbon-based materials include carbon nanotubes modified by functional groups, reagents, or materials; graphene, graphene oxide, and reduced graphene oxide; carbon derived from a gold organic framework; activated carbon biochar; and nanodiamond. The harmful substances in food samples include esters, mycotoxins, polycyclic aromatic hydrocarbons, antibiotics, alkaloids, phenols, vitamins, and antibiotics. Based on the classification of carbon-based materials, this review reveals that carbon-based magnetic materials have good preconcentration ability for harmful substances in food samples. MSPE can be combined with GC-MS, liquid chromatography-high resolution mass spectrometry (LC-HRMS), ultra-fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS), ultra high performance liquid chromatography-Q-Exactive high resolution mass spectrometry (UHPLC-Q-Exactive HRMS), high performance liquid chromatography-diode array detection (HPLC-DAD), gas chromatography micro-electron capture detection (GC-µECD), high performance liquid chromatography fluorescence with post-column photochemical derivatization (HPLC-PCD-FLD), and HPLC-UV to analyze food samples. These combined technologies have high accuracy and recovery. However, the synthesis methods of carbon-based magnetic materials such as carbon nanotubes and graphene, incur high energy consumption and high cost, and involve complex processes, which limit their application. Therefore, a carbon-based magnetic adsorbent with low cost, high selectivity, and high extraction efficiency was developed by further exploring functional modification with biochar as a carbon base. This is a very promising direction to develop MSPE technology utilizing biochar-based magnetic materials for food sample pretreatment. This review provides a theoretical basis and technical support for the wide application of carbon-based magnetic materials in MSPE technology for food analysis.

On-site sample preparation of trace aromatic amines in environmental waters with monolith-based multichannel in-tip microextraction apparatus followed by HPLC determination.

A novel on-site preparation strategy for the determination of trace aromatic amines (AAs) in environmental waters was developed in the present study. To extract AAs effectively, 4-vinylbenzoic acid was copolymerized with ethylene dimethacrylate (ED)/divinylbenzene (DVB) in a pipette tip to obtain a new monolith-based adsorbent (MBA). The MBAs were employed as the extraction phases of home-made multichannel in-tip microextraction apparatus (ITMA) which was used to perform field sample preparation of AAs in different water samples followed by HPLC/DAD analysis. Due to the abundant functional groups, the prepared MBA displayed satisfying extraction performance for studied AAs. Under the optimized conditions, limits of detection varied from 2.1 to 26 ng/L with good coefficients of determination and precision. The recoveries for real water samples with different fortified concentrations were in the range of 78.1-119%, and the RSD values varied from 0.85 to 11%. In addition, the results achieved with the introduced method were well comparable to that obtained with conventional laboratory sample pretreatment process. Compared with existing approaches, the proposed method exhibits some merits such as s high throughput, good sensitivity and eco-friendliness. Most of important, the MBA/ITMA for on-site preparation avoids the storage and transportation of large volumes of waters, and guarantees the analytical accuracy of studied AAs.

Metal-organic framework-monolith composite-based in-tube solid phase microextraction on-line coupled to high-performance liquid chromatography-fluorescence detection for the highly sensitive monitoring of fluoroquinolones in water and food samples.

In this study, a new metal-organic framework-monolith composite for in-tube solid phase microextraction phase (IT-SPME) of fluoroquinolones (FQs) was prepared. 4-Vinylbenzoic acid was copolymerized with ethylenedimethacrylate in a fused silica capillary to form porous monolith. After that, zeolitic imidazolate frameworks (ZIF-8) were synthesized in situ within the pores and the surface of the monolith by controlled layer-by-layer self-assembly of Zn2+ and imidazole. The introduction of ZIF-8 enhanced the surface area of monolith composite, and thus, improving the extraction performance of IT-SPME for FQs obviously. Under the optimized conditions, a highly sensitive method for the monitoring of FQs residue in water and honey samples was developed by the on-line combination of IT-SPME with high-performance liquid chromatography with fluorescence detection (HPLC-FLD). The limits of detection (S/N = 3) for the targeted FQs in water and honey samples were as low as 0.14-0.61 ng/L and 0.39-1.1 ng/L, respectively. The relative standard deviations (RSDs) for intra-day and inter-day assay variability were less than 10% in all samples. The established on-line IT-SPME-HPLC-FLD was successfully used to detect ultra-trace FQs in environmental water and honey samples. Recoveries at different spiked concentrations ranged from 80.1% to 119% and 80.2-117% for water and honey samples, respectively, with satisfactory reproducibility. Compared to up-to-date reported methods, the proposed approach exhibits some features such as high sensitivity, convenience, partial automation, low consumptions of sample and solvent.

Dual functional monomers modified magnetic adsorbent for the enrichment of non-steroidal anti-inflammatory drugs in water and urine samples.

According to the molecular properties of non-steroidal anti-inflammatory drugs (NSADs), a new adsorbent for magnetic solid phase extraction (MSPE) was designed and synthesized. Triethyl-(4-vinylbenzyl)aminium chloride and 4-vinylbenzeneboronic acid were utilized as dual functional monomers to copolymerize with divinylbenzene on the surface of pre-modified Fe3O4 nanoparticles. The prepared magnetic adsorbent (Fe3O4@TCVA) was characterized by elemental analysis, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometer. Due to the abundant boronic acid, quaternary amine and phenyl groups, the Fe3O4@TCVA displayed satisfactory extraction performance for target NSADs (diclofenac acid, ibuprofen and mefenamic acid) by means of B-N coordination, anion-exchange, π-π and hydrophobic interactions. Under the optimized conditions, the Fe3O4@TCVA/MSPE was combined with high-performance liquid chromatography with diode array detection (HPLC-DAD) to sensitively analyze NSADs in water and human urine samples. Results indicated that the limits of detection for water and urine samples were in the ranges of 0.014-0.031 µg/L and 0.029-0.11 µg/L, respectively. The relative standard deviations for the intra-day and inter-day assay variability were below 10%. The applicability of the proposed Fe3O4@TCVA/MSPE-HPLC-DAD method was demonstrated by the successful extraction and quantification of trace levels of NSADs in real water and human urine samples. Satisfactory spiked recovery and reproducibility were achieved.

Fabrication of N,N-dimethyldodecylamine functionalized magnetic adsorbent for efficient enrichment of flavonoids.

A new N,N-dimethyldodecylamine functionalized magnetic adsorbent (Fe3O4@MDHM) was fabricated and used for the efficient enrichment of flavonoids under the format of magnetic solid phase extraction (MSPE). Different techniques were utilized to characterize the spectroscopic, morphology and magnetic properties of the prepared adsorbent. Under the optimized extraction conditions, the Fe3O4@MDHM displayed satisfactory enrichment performance to flavonoids by means of hydrophobic, ion-exchange and electrostatic interactions. Furthermore, a sensitive, quick and environmentally friendly analytical method for the determination of flavonoids in grape juice was established by the combination of Fe3O4@MDHM/MSPE with high performance liquid chromatography-diode array detection (HPLC-DAD). Results indicated that the linear ranges for target analytes were in the range of 0.5-200.0 µg/L, with good correction coefficients (R2＞0.99). The limits of detection (S/N = 3) and limits of quantification (S/N = 10) for flavonoids were in the ranges of 0.080-0.12 µg/L and 0.27-0.40 µg/L, respectively. The quantification of flavonoids in real grape juices were used to inspect the applicability of proposed Fe3O4@MDHM/MSPE-HPLC-DAD method. As a new MSPE adsorbent, the Fe3O4@MDHM exhibited some merits such as quick extraction procedure (extraction time, 13 min), high enrichment performance (enrichment factors, 60-69), low consumption of organic solvent (0.49 mL methanol) for the separation and determination of flavonoids.

In situ tracing the process of human enamel demineralization by electrochemical impedance spectroscopy (EIS).

OBJECTIVE: The purpose of this study was to in situ characterize the demineralization (namely dissolution of hydroxyapatite) on the surface of the human enamel using electrochemical impedance spectroscopy (EIS) technology. METHODS: Fresh human third molars extracted without visible evidence of caries, were used in this study. After they were immersed in a demineralizing solution prepared from lactic acid and carboxy methyl cellulose sodium (Na-CMC) buffering at pH 4, demineralization happened on their surfaces. EIS of the specimens were measured at a series of immersed interval. X-ray diffractometer (XRD) were used to distinguish the microstructure of the surface layer of the specimens. The depositions that appeared in the demineralizing solution after 46 h immersion were analyzed by fourier transform infrared spectrometer (FTIR). RESULTS: XRD analysis revealed that the percentage of intensity (I%) of HAP gradually decreased with the elapsed immersing time, which indicated the dissolution of HAP columns of enamel. Nyquist spectra were fitted with an equivalent circuit characterized by some parameters, such as Q and R(p) (error<0.1%). Changes of the parameters' values revealed that the rate of demineralization accelerated at the forepart of the demineralization, but slowed down beyond 70 h immersion. CONCLUSIONS: The results suggested that EIS was proved to be a useful method for in situ investigating and in vivo detecting the demineralization of the enamel.

Extraction of triazole fungicides in environmental waters utilizing poly (ionic liquid)-functionalized magnetic adsorbent.

This work prepared a new poly (ionic liquid)-functionalized magnetic adsorbent (PFMA) for the extraction of triazole fungicides (TFs) in environmental waters prior to determination by high performance liquid chromatography/diode array detection (HPLC-DAD). A polymerizable ionic liquid, 1-methyl-3-allylimidazolium bis(trifluoromethylsulfonyl)imide was employed to copolymerize with divinylbenzene on the surface of modified magnetite to fabricate the PFMA. The morphology, spectroscopic and magnetic properties of the new adsorbent were investigated by different techniques. A series of key parameters that influence the extraction performance including the amount of PFMA, desorption solvent, adsorption and desorption time, sample pH value and ionic strength were optimized in detail. Under the optimum conditions, the prepared PFMA could extract targeted TFs effectively and quickly under the format of magnetic solid-phase extraction (MSPE). Satisfactory linearities were achieved in the range of 0.1-200.0µg/L for triadimenol and 0.05-200.0µg/L for other TFs with good coefficients of determination above 0.99 for all analytes. The limits of detection (S/N=3) and limits of quantification (S/N=10) for TFs were in the range of 0.0050-0.0078µg/L and 0.017-0.026µg/L, respectively. Environmental waters including lake, river and well waters were used to demonstrate the applicability of developed MSPE-HPLC-DAD method, and satisfactory recoveries and repeatability were obtained.

Fabrication of polymeric ionic liquid-modified magnetic adsorbent for extraction of apolar and polar pollutants in complicated samples.

A new polymeric ionic liquid-modified magnetic adsorbent (PIL-MA) was successfully fabricated and used to extract apolar and polar pollutants with magnetic solid-phase extraction (MSPE). The PIL-MA was prepared by simple free radical copolymerization of 1-vinylbenzyl-3-methylimidazolium hexafluorophosphate, divinylbenzene and silica-coated magnetite. Several characterized techniques including infrared spectroscopy, elemental analysis, scanning electron microscopy, transmission electron microscopy and magnetic measurement were used to characterize the PIL-MA. Parabens and aromatic amines were selected as test analytes to investigate the extraction performance of PIL-MA for apolar and strongly polar analytes, respectively. The extraction parameters including the amount of PIL-MA, adsorption time, desorption solvent and time, pH value and ionic strength were optimized thoroughly. At the same time, convenient and sensitive analytical methods for parabens and aromatic amines in real samples were developed by the combination of PIL-MA-MSPE and HPLC-DAD. Results well demonstrate that there are abundant active groups in the PIL-MA and multiply interactions including π-π, hydrophobic, hydrogen-bonding and dipole-dipole are involved in the extraction.

Kinetic model for hydroxyapatite precipitation on human enamel surface by electrolytic deposition.

The electrolytic deposition (ELD) of hydroxyapatite (HAP) coating on human enamel surface for different loading times at varied temperatures (ranging from 37 degrees C to 85 degrees C) and varied current densities (ranging from 0.05 mA cm(-2) to 10 mA cm(-2)) was investigated in this study. Thin film x-ray diffraction, Fourier transform infrared and micro-Raman spectra analysis, as well as an environmental scanning electron microscope, were used to characterize the coating. The results showed that only the HAP phase occurred on the enamel surface after ELD experiments. The contents of HAP deposits on the enamel surface linearly changed proportional to the square root of the loading time, which was in good agreement with the kinetic model of ELD of HAP coating based on one-dimensional diffusion. The induction periods were observed on all the regression lines, and the rate of the HAP coating formation on enamel showed a linear relationship with the current density. It was implied that the diffusion process was the rate-determining step in the ELD of the HAP coating on human enamel.

Synthesis and structure of cerium-substituted hydroxyapatite.

The aim of this study was to explore the effect of cerium ions on the formation and structure of hydroxyapatite (HAP). All particles, prepared by hydrothermal method, were synthesized at varied X(Ce) = Ce/(Ca + Ce) (from 0 to 10%) with the atomic ratio (Ce + Ca)/P fixed at 1.67. Their morphology, composition and crystal structure were characterized by TEM, EPMA, XRD and FTIR. The results showed that in this composition range the apatite structure is maintained, Ce3+ ions could enter the crystal lattice of apatite and substitute Ca2+ ions. The doping of Ce3+ ions resulted in the decrease of the crystallite size with increase in X(Ce). The HAP particles without doping were short rods having a diameter from 10 to 20 nm and a length from 30 to 50 nm. They grew into long needles upon increasing X(Ce).