Methacrylate bonded covalent organic framework monolithic column online coupling with high-performance liquid chromatography for analysis of trace estrogens in food.

Covalent organic frameworks (COFs) are a burgeoning class of crystalline porous materials with unique properties and have been considered as a promising functional extraction medium in sample pretreatment. In this study, a new methacrylate-bonded COF (TpTh-MA) was well designed and synthesized via the aldehyde-amine condensation reaction, and the TpTh-MA was incorporated into poly (ethylene dimethacrylate) porous monolith by a facile polymerization reaction inside capillary to prepare a novel TpTh-MA monolithic column. The fabricated TpTh-MA monolithic column was characterized with scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and N2 adsorption-desorption experiments. Then, the homogeneous porous structure, good permeability and high mechanical stability of TpTh-MA monolithic column was used as separation and enrichment media of capillary microextraction, which was coupled with high-performance liquid chromatography fluorescence detection for online enrichment and analysis of trace estrogens. The main experimental parameters influencing the extraction efficiency were systematically investigated. The adsorption mechanism for three estrogens was also explored and discussed based on hydrophobic effect, π-π affinity and hydrogen bonding interaction, which contributed to its strong recognition affinity to target compounds. The enrichment factors of the TpTh-MA monolithic column micro extraction method for the three estrogens were 107-114, indicating a significant preconcentration ability. Under optimal conditions, a new online analysis method was developed and exhibited good sensitivity and wide linearity range of 0.25-100.0 µg·L-1 with a coefficient of determination (R2) higher than 0.9990 and a low limit of detection with 0.05-0.07 µg·L-1. The method was successfully applied for online analysis of three estrogens of milk and shrimp samples and the recoveries obtained from spiking experiments were in range of 81.4-113% and 77.9-111%, with the relative standard deviations of 2.6-7.9% and 2.1-8.3% (n = 5), respectively. The results revealed the great potential for the application of the COFs-bonded monolithic column in the field of sample pretreatment.

Purification of biflavonoids from Selaginelladoe derleinii Hieron by special covalent organic polymers material.

Herein, a novel covalent organic polymers (COP) material based on acylhydrazone bond (AB-COP) was prepared as an efficient extraction material for enriching natural medicine biflavonoids from Selaginella doederleinii Hieron. The obtained AB-COP structure was characterized in detail. And it was the first time to investigate the effect of AB-COP on the adsorption of biflavonoids. The effects of initial concentration of solution, adsorption temperature, solid-liquid ratio, adsorption time on the adsorption of biflavonoids were studied. In addition, adsorption kinetic model, adsorption thermodynamic model and density functional theory (DFT) were also investigated to evaluate the adsorption mechanism. At the same time, the static desorption and reusability of AB-COP were investigated. Finally, the dynamic enrichment effect of AB-COP for biflavonoids was investigated. The results showed that AB-COP was successfully synthesized by Fourier transform infrared spectroscopy (FT-IR), solid state nuclear magnetism (NMR), X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), laser particle size analysis and Brunner Emmet Teller (BET) specific surface area test. The optimized adsorption parameters of AB-COP were initial concentration of 0.5 mg/mL, temperature of 45 °C, solid-liquid ratio of 10:10 (mg/mL), adsorption time of 60 min. The Langmuir adsorption isotherm could effectively describe the adsorption process, the pseudo-secondary adsorption model could accurately explain the adsorption mechanism, and the DFT calculations revealed that the interaction forces of AB-COP and biflavonoids were π-π stacking and hydrogen bonding. In addition, AB-COP successfully resolved biflavonoids through urea-methanol (1.3 mol/L), and the material can be reused at least four times. Finally, the solid phase extraction (SPE) chromatographic column prepared by AB-COP was successfully applied to the enrichment of biflavonoids from S. doederleinii, and the effect was significantly better than traditional chromatography materials, andthis method was also successfully applied to the enrichment of flavonoids in other plant extracts including Flos sophorae, Pericarpium viride, Lophatheri herba, Herba cuscutae. These results provide references for further purification of bioactive ingredients from plant extracts by using AB-COP.

ß-Ketoenamine-linked covalent organic framework absorbent for online micro-solid phase extraction of trace levels bisphenols in plastic samples.

Covalent organic frameworks with tunable porous crystallinity and outstanding stability have exhibited fascinating pretreatment performance as ideal extraction media. Herein, the ß-ketoenamine-linked TpPa-1 synthesized by 1,3,5-triformylphloroglucinol and paraphenylenediamine was employed as the absorbent for online micro-solid phase extraction of trace bisphenols combined with high-performance liquid chromatography detection. A series of characterizations indicated that the TpPa-1 possessed large surface areas, high stability, and hydrophobicity. The main experimental parameters affecting the extraction efficiency were optimized in detail. Compared with four commercial sorbents, the TpPa-1 exhibited superior enrichment capacity for extracting bisphenols. Under the optimum conditions, the established method demonstrated a wide linear range and high sensitivity with the limit of detection ranging from 0.05-0.06 µg/L. Furthermore, the developed method was successfully applied to determine bisphenols in plastic samples. Bisphenol A was actually detected in a transparent box with a concentration of 0.31 µg/g, and the recoveries of the four bisphenols in the plastic samples were 80.5-116% with the relative standard deviation less than 9.2%. Such performance was attributed to recognition affinity, including the π-π affinity, hydrophobic effect, and hydrogen bond. These results demonstrated that TpPa-1 possessed great potential to be an excellent pretreatment medium for online separation and analysis of trace analytes in complex samples.

[Application of imine covalent organic frameworks in sample pretreatment].

Imine covalent organic frameworks (I-COFs), including imine-linked COFs and hydrazone-linked COFs, are a new type of crystalline porous organic materials constructed by the condensation of organic monomers by the Schiff-base reaction. Because they are composed of lightweight elements linked by strong covalent bonds, I-COF materials possess the advantages of low skeleton density, large surface area, high porosity, abundant monomer species, controllable pore size, functionalized structure, diverse synthetic methods, excellent adsorption performance, outstanding physical and chemical stabilities, etc. In recent years, interest in the field of I-COFs has increased tremendously because of their exceptional performance and broad applications in gas storage, gas separation, catalysis, sensing, photoelectric materials, sample pretreatment, drug delivery, and other fields. To date, imine bonds are one of the most widely used covalent bonds in COFs, and represent one of the most important ways to obtain I-COFs with excellent chemical stabilities. The synthesis methods for I-COFs include solvothermal synthesis, microwave synthesis, mechanochemical grinding synthesis, and room-temperature synthesis methods. Solvothermal synthesis is the most extensively used method for the production of I-COFs with high specific surface areas and good thermal stabilities. The microwave synthesis method is conducive to the rapid synthesis of COFs in industry, providing a more time-saving, simpler, and safer route for large-scale preparation of I-COFs. The mechanochemical grinding synthesis of porous solids has gained importance as an alternative to conventional solvothermal synthesis, because the process is quick, environment-friendly, and potentially scalable. The room-temperature method is characterized by mild reaction conditions and rapid reactions. It is an energy-saving, economic, safe, and green synthesis method, which has emerged as a hot spot in the preparation of I-COFs in recent years. Research progress over the past years on the application of I-COFs in the field of materials science has undoubtedly established the basis of its application in analytical chemistry. Owing to the excellent physical and chemical properties of I-COF materials, they are suitable for use as separation and enrichment media for trace target compounds in complex samples. The high specific surface area and porosity, extended conjugate network skeleton, and π-electron-rich nature of the materials endow it with a high adsorption capacity. These materials are highly enriched in target analytes by π-π interactions, acid-base interactions, donor-acceptor interactions, hydrogen bonding, hydrophobic interactions, and other intermolecular interactions. Precise control of the microporous structure of I-COFs was obtained by controlling the chain length, geometric structure, doping elements, and substituent groups of the organic monomers. Selective enrichment of target trace substances was achieved by modifying the groups of I-COFs based on the principle of host guest adaptation, molecular sieving, or microporous filling effect. At present, research on the synthesis of I-COF materials is in the stage of rapid development, and many I-COFs with excellent properties and great application potential have been synthesized, allowing widespread application of I-COFs in sample pretreatment medium. This review summarizes the current state-of-the-art on the main types and synthetic methods of I-COFs, as well as the applications of I-COFs in solid-phase extraction, magnetic solid-phase extraction, dispersive solid-phase extraction, and solid-phase microextraction. The prospects of I-COFs in sample pretreatment are also presented.

Regularities of element migration based on rock spectral features: a case study of the Liwu copper deposit.

The Liwu copper-zinc mining area has a complex topographical environment. Using traditional prospecting methods, it is difficult and costly to carry out traditional prospecting research on a large scale. This study used portable X-ray fluorescence (pXRF) spectrometry and hyperspectral imaging for analysing rock samples in the B2 ore body of the Liwu copper-zinc deposit. The hyperspectral imaging data and the measured indoor spectral characteristic curve of the same lithological rock have a certain similarity. The absorption or reflection characteristics in the same waveband were similar. The main elements were Cu and Zn in the ore body, Pb which was obviously brought out, and Cd, Sn and Sb which were brought in. It is believed that the mass migration of Cd, Sn, Sb and Pb elements plays an important role in the precipitation and enrichment of Cu and Zn elements. This method can be used to quickly determine element migration. The combination of the two analytical methods of pXRF and hyperspectral analysis, the low requirements of the work site and the fast and efficient characteristics, mean this method has unique advantages in analysing and monitoring environmental pollution, rock and mineral analysing and prospecting.

Annual Characteristics, Source Analysis of PM1-Bound Potentially Harmful Elements in the Eastern District of Chengdu, China.

Chengdu, a megacity in southwestern China, experiences severe air pollution; however, knowledge of the seasonal variation in mass concentration, extent of potentially harmful elements (PHEs) contamination, and sources caused by heavy metals remains lacking. This study adopted a weighting method to calculate the daily mass concentration of PM1 and used ICP-MS to determine PHE concentrations. Results indicated that PM1 mass concentration was in the range 5.44-105.91 µg/m3. Seasonal PM1 mass concentration could be arranged in the following order: winter > fall > spring > summer. The concentrations of PHEs in the PM1 sample mostly showed the same seasonal variation characteristics as mass concentration. The average concentration of each PHE decreased as follows: Cu (107.44) > Zn (81.52) > Pb (22.04) > As (8.17) > Sb (1.91) > Ni (1.87) > Cr(VI) (0.84) > Cd (0.40) > Tl (0.33) (ng/m3). Enrichment factor values varied markedly from mild to anomalous enrichment. Principal component analysis revealed mainly derived from the fossil fuel combustion (55.215%).

A Facile One-Pot Synthesis of Biomimetic Photocatalyst Zn(II)-Porphyrin-Sensitized 3D TiO2 Hollow Nanoboxes and Synergistically Enhanced Visible-Light Degradation.

A serials of biomimetic photocatalyst zinc(II) meso-tetra(4-carboxyphenyl)porphyrinato (ZnTCP)-sensitized 3D hierarchical TiO2 hollow nanoboxes (TiO2-HNBs) assembled by six ordered nanosheets with dominant {001} facets exposure (ZnTCP@TiO2-HNBs) have been successfully synthesized by a facile one-pot solvothermal method via a topological transformation process with TiOF2 as template. Infrared spectra (IR), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirmed that ZnTCP played a decisive role in constructing 3D hollow nanoboxes through the formation of ester bond combined to TiO2-HNBs, which also provided a transferring photo excited electrons bridge to sensitize TiO2-HNBs for enhancing visible-light response. Due to the superior sensitization and biomimetic activity of ZnTCP, the photodegradation rate of rhodamine B (RhB) of as-prepared ZnTCP@TiO2-HNBs with ZnTCP/TiOF2 mass ratio of 2% (T-2p) improves 3.6 times compared to that of TiO2-HNBs with a degradation yield of 99% for 2 h under simulated sunlight irradiation (> 420 nm). The enhanced photodegradation ability was attributed to synergistic visible photocatalytic mechanism of biomimetic catalyst, which can not only produce hydroxyl radical (•OH) and superoxide radical (•O2-) coming from the excitation process of ZnTCP sensitized TiO2-HNBs, but also generate singlet oxygen (1O2) that was only provided by biomimetic enzyme porphyrins. Furthermore, the photocatalyst showed good recycling stability and dispersibility after five rounds, ascribed to ZnTCP strong chemical bonding to the support TiO2-HNBs. By means of electrochemical cyclic voltammetry analysis, the effect of central zinc ions and parent porphyrin rings on the redox property of biomimetic catalyst was studied.

One-step topological preparation of carbon doped and coated TiO2 hollow nanocubes for synergistically enhanced visible photodegradation activity.

Various three-dimensional TiO2 hollow structures have attracted strong scientific and technological attention due to their excellent properties. 3D hierarchical TiO2 hollow nanocubes (TiO2-HNBs) are not good candidates for industrial photocatalytic applications due to their large energy gap which is only activated by UV light. Herein, visible-light-responsive carbon doped and coated TiO2-HNBs (C@TiO2-HNBs) with a dominant exposure of {001} facets have been prepared via a template-engaged topotactic transformation process using facile one-step solvothermal treatment and a solution containing ethanol, glucose and TiOF2. The effects of reaction time and glucose/TiOF2 mass ratio on the structure and performance of C@TiO2-HNBs were systematically studied. We found that glucose played an important role in providing H2O during the topological transformation from self-templated TiOF2 cubes into 3D hierarchical TiO2 hollow nanocubes versus dehydration reactions, where its main function was as a carbon source. Coated carbon was deposited predominantly on the surface as sp2 graphitic carbon in extended p conjugated graphite-like environments, and doped carbon mainly replaced Ti atoms in the surface lattice to form a carbonate structure. The results were confirmed using TEM SEM, EDS, XRD, FT-IR, XPS and Raman spectroscopic studies. The C@TiO2-HNBs achieved greatly improved RhB photodegradation activity under visible light irradiation. The catalyst prepared with glucose/TiOF2 at a mass ratio of 0.15 (T24-0.15) showed the highest photodegradation rate of 96% in 40 min, which is 7.0 times higher than those of the TiO2-HNBs and P25. This new synthetic approach proposes a novel way to construct carbon hybridized 3D hierarchical TiO2 hollow nanocubes by combining two modification methods, "element doped" and "surface sensitized", at the same time.

Acylhydrazone bond dynamic covalent polymer gel monolithic column online coupling to high-performance liquid chromatography for analysis of sulfonamides and fluorescent whitening agents in food.

A new dynamic covalent polymer (DCP) gel was well designed and constructed based on imine chemistry. Polycondensation of 4,4'-biphenyldicarboxaldehyde and 1,3,5-benzenetricarbohydrazide via Schiff-base reaction resulted in an acylhydrazone bond gel (AB-gel) DCP. AB-gel DCP had three-dimensional network of interconnected nanoparticles with hierarchically porous structure. AB-gel DCP was successfully fabricated as a monolithic column by an in-situ chemical bonding method for online enrichment and separation purpose with excellent permeability. AB-gel DCP based monolithic column showed remarkable adsorption affinity towards target analytes including sulfonamides (SAs) and fluorescent whitening agents (FWAs) due to its strong π-π affinity, hydrophobic effect and hydrogen bonding interaction. Then, AB-gel DCP based monolithic column was applied for online separation and analysis of trace SAs and FWAs in food samples coupled with high-performance liquid chromatography (HPLC). Sulfathiazole (ST) and sulfadimidine (SM2) in one positive weever sample were actually found and determined with concentrations of 273.8 and 286.3µg/kg, respectively. 2,5-Bis(5-tert-butyl-2-benzoxazolyl) thiophene (FWA184) was actually quantified in one tea infusion sample with the concentration of 268.5ng/L. The spiked experiments suggested the good recoveries in range of 74.5-110% for SAs in weever and shrimp samples with relative standard deviations (RSDs) less than 9.7% and in range of 74.0-113% for FWAs in milk and tea infusion samples with RSDs less than 9.0%. AB-gel DCP monolithic column was proved to be a promising sample preparation medium for online separation and analysis of trace analytes in food samples with complex matrices.

Characteristics, Sources and Health Risk Assessment of Trace Metals in PM10 in Panzhihua, China.

Ambient PM10 air samples were collected at two industrial sites and one urban residential site in the mining city of Panzhihua, China, from April, 2014, to January, 2015. Mass concentrations of ten trace metals (As, Cd, Cr, Ni, Co, V, Mn, Cu, Pb, and Zn) in PM10 were determined by inductively coupled plasma-mass spectrometry. The results showed Zn, Pb, Cu, Mn and V were the most abundant elements from the industrial sites. Concentrations for Cd, Cr, Co, Ni, Mn and Cu at industrial sites greatly exceeded the air quality standards of the World Health Organization and the Chinese Ministry of Environmental Protection. Principal component analysis indicated that the main sources of the trace metals were steel smelting, fuel combustion, geological and mineral dust. Four different clusters of particles (i.e., mineral, calcium-containing, soot and aluminosilicate) were identified by scanning electron microscopy coupled with energy dispersive X-ray spectrometry. Chromium (Cr) was found to present the highest excess cancer risk, implying the potential for carcinogenic health effects in local inhabitants. Manganese (Mn) presented a non-carcinogenic health risk to children and adults, while the other metals were within acceptable limits.

A hydrazone covalent organic polymer based micro-solid phase extraction for online analysis of trace Sudan dyes in food samples.

Covalent organic polymers (COPs) connected by covalent bonds are a new class of porous network materials with large surface area and potential superiority in sample pretreatment. In this study, a new hydrazone linked covalent organic polymer (HL-COP) adsorbent was well-designed and synthesized based on a simple Schiff-base reaction. The condensation of 1,4-phthalaldehyde and 1,3,5-benzenetricarbohydrazide as organic building blocks led to the synthesis of HL-COP with uniform particle size and good adsorption performance. This HL-COP adsorbent with high hydrophobic property and rich stacking π electrons contained abundant phenyl rings and imine (CN) groups throughout the entire molecular framework. The adsorption mechanism was explored and discussed based on π-π affinity, hydrophobic effect, hydrogen bonding and electron-donor-acceptor (EDA) interaction, which contributed to its strong recognition affinity to target compounds. Enrichment factors were 305-757 for six Sudan dyes by HL-COP micro-solid phase extraction (µ-SPE), indicating its remarkable preconcentration ability. Furthermore, the adsorption amounts by HL-COP µ-SPE were 1.0-11.0 folds as those by three commonly used commercial adsorbents. Then, HL-COP was applied as adsorbent of online µ-SPE coupled with high performance liquid chromatography (HPLC) for enrichment and analysis of trace Sudan dyes in food samples with detection limit of 0.03-0.15µg/L. The method was successfully applied for online analysis of chilli powder and sausage samples. Sudan II and Sudan III in one positive chilli powder sample were actually found and determined with concentrations of 8.3 and 6.8µg/kg, respectively. The recoveries of chilli powder and sausage samples were in range of 75.8-108.2% and 73.8-112.6% with relative standard deviations of 1.2-8.5% and 1.9-9.4% (n=5), respectively. The proposed method was accurate, reliable and convenient for the online simultaneous analysis of trace Sudan dyes in food samples.

Preparation of sulfonated graphene/polypyrrole solid-phase microextraction coating by in situ electrochemical polymerization for analysis of trace terpenes.

In this study, a novel sulfonated graphene/polypyrrole (SG/PPy) solid-phase microextraction (SPME) coating was prepared and fabricated on a stainless-steel wire by a one-step in situ electrochemical polymerization method. Crucial preparation conditions were optimized as polymerization time of 15min and SG doping amount of 1.5mg/mL. SG/PPy coating showed excellent thermal stability and mechanical durability with a long lifespan of more than 200 stable replicate extractions. SG/PPy coating demonstrated higher extraction selectivity and capacity to volatile terpenes than commonly-used commercial coatings. Finally, SG/PPy coating was practically applied for the analysis of volatile components from star anise and fennel samples. The majority of volatile components identified were terpenes, which suggested the ultra-high extraction selectivity of SG/PPy coating to terpenes during real analytical projects. Four typical volatile terpenes were further quantified to be 0.2-27.4µg/g from star anise samples with good recoveries of 76.4-97.8% and 0.1-1.6µg/g from fennel samples with good recoveries of 80.0-93.1%, respectively.

Review of online coupling of sample preparation techniques with liquid chromatography.

Sample preparation is still considered as the bottleneck of the whole analytical procedure, and efforts has been conducted towards the automation, improvement of sensitivity and accuracy, and low comsuption of organic solvents. Development of online sample preparation techniques (SP) coupled with liquid chromatography (LC) is a promising way to achieve these goals, which has attracted great attention. This article reviews the recent advances on the online SP-LC techniques. Various online SP techniques have been described and summarized, including solid-phase-based extraction, liquid-phase-based extraction assisted with membrane, microwave assisted extraction, ultrasonic assisted extraction, accelerated solvent extraction and supercritical fluids extraction. Specially, the coupling approaches of online SP-LC systems and the corresponding interfaces have been discussed and reviewed in detail, such as online injector, autosampler combined with transport unit, desorption chamber and column switching. Typical applications of the online SP-LC techniques have been summarized. Then the problems and expected trends in this field are attempted to be discussed and proposed in order to encourage the further development of online SP-LC techniques.

[Progresses on the applications of microporous organic polymers in sample preparation techniques].

Microporous organic polymers (MOPs) are a class of novel porous materials consisting of the lighter elements, which possess low framework density, large surface area, tunable pore size and structure, excellent chemical and physical stability. In recent years, MOPs have shown great potential in the field of sample preparation techniques. In this paper, the classification and synthetic methods of MOPs are summarized, and the applications of MOPs in sample preparation techniques such as solid phase extraction, batch adsorption experiments, monolith and sensing film are reviewed.

Application of scenario analysis and multiagent technique in land-use planning: a case study on Sanjiang wetlands.

Land-use planning has triggered debates on social and environmental values, in which two key questions will be faced: one is how to see different planning simulation results instantaneously and apply the results back to interactively assist planning work; the other is how to ensure that the planning simulation result is scientific and accurate. To answer these questions, the objective of this paper is to analyze whether and how a bridge can be built between qualitative and quantitative approaches for land-use planning work and to find out a way to overcome the gap that exists between the ability to construct computer simulation models to aid integrated land-use plan making and the demand for them by planning professionals. The study presented a theoretical framework of land-use planning based on scenario analysis (SA) method and multiagent system (MAS) simulation integration and selected freshwater wetlands in the Sanjiang Plain of China as a case study area. Study results showed that MAS simulation technique emphasizing quantitative process effectively compensated for the SA method emphasizing qualitative process, which realized the organic combination of qualitative and quantitative land-use planning work, and then provided a new idea and method for the land-use planning and sustainable managements of land resources.