Metal-organic frameworks (MOFs) are a class of crystalline materials built from organic binding ligands and metal ions through self-assembly. Currently, MOFs have drawn a growing interest among the scientific teams of various fields. Compared with conventional inorganic porous materials, MOFs possess larger specific surface areas, higher porosity and diversity of structures and functions, thus many potential applications have been proposed in the domains of gas adsorption and separation, sensors, drug delivery, catalysis or others. The combinations of MOFs and other materials such as graphene oxide, magnetic nanoparticles have obvious advantages in adsorption and separation. The appearance of novel materials greatly promotes interdisciplinary developments such as organic chemistry, inorganic chemistry, coordination chemistry, materials chemistry, life science and computer science. This article reviews the progress of MOFs in recent years, including the characteristics of MOFs, advances at home and abroad, applications, central issues of compound MOFs and the prospects in the future.
Molecularly imprinted microspheres (MIPMs) for binding and recognition of nicosulfuron (NS) (NS-MIPMs) were prepared by precipitation polymerization. Methacrylic acid (MAA) was used as the functional monomer, trimethylolpropane trimethacrylate (TRIM) as the linking agent, 2,2-azobisisobutyronitrile (AIBN) as the initiator and chloroform as the porogenic solvent. The preparation conditions were optimized, and MIPMs exhibited the best adsorption capacity when the molar ratio of NS/MAA/TRIM/AIBN was 1:4:4:1 and the volume of the porogenic solvent was 90 mL. An ultraviolet-visible (UV-Vis) spectrophotometer was employed to study the mechanism of the interaction between NS and MAA, and the results showed that the NS-MAA complexes of 1:1 molar ratio were obtained in the pre-polymerization phase. The rebinding capacity of MIPMs was evaluated according to adsorption kinetics and adsorption isotherm of the imprinted microspheres. The Scatchard plot revealed that the template polymer system has a two-site binding behavior and the MIPMs exhibited the maximum rebinding to NS at 11370.5 μg/g. The MIPMs were then used as adsorbents in a solid phase extraction (SPE) column and the optimum loading, washing and eluting conditions for the MIPMs were established. Additionally, a rapid method for the determination of NS residues in soil was developed using an NS-MIPMs SPE column. The analyte was extracted using acetonitrile and phosphate buffer, cleaned-up by an NS-MIPMs SPE column and analyzed by HPLC. The results showed that good linearity was observed in the range of 0.01-1 mg/L for NS, with a correlation coefficient of 0.9986. The recovery tests were performed at the spiked levels of 0.02-1 mg/kg, and the recoveries were in the range of 82.2%-86.3% with the relative standard deviations of 1.9%-4.3%. The advantages of the proposed method are that it is easy to operate, reliable and applicable to analyze the NS residues in soil samples.
Gastric cancer is one of the most common malignant and the second most frequent cause of cancer-related mortality in the world. Noninvasive screen methods including tumor markers are intensively needed in the clinic. To discover metabolic markers for gastric cancers, the sera metabolic profiles of 20 gastric cancer (GC) patients and 40 healthy controls were analyzed by liquid chromatography coupled with mass spectrometry (LC-MS) using a pseudotargeted approach. The results of principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) indicated that obvious classification could be observed between GC and the healthy controls. According to the results of non-parametric statistical test, 57 ions were identified among all the differential metabolic features. Of all the identified differential metabolites, dihydrocholesterol provide good diagnostic performance of GC, which was also validated by another cohort including the 20 gastric cancer patients and the 39 healthy controls. With this robust pseudotargeted approach, our study provides both potential tumor markers and the basis for the metabolic phenotype of gastric cancers.
A rapid method has been developed for the determination of aflatoxins B1, B2, G1 and G2, ochratoxin A, zearalenone, T-2 toxin, deoxynivalenol and fumonisin B1 in cereal-based complementary foods for infants and young children. The mycotoxins were extracted from the samples using a modified QuEChERS-based extraction procedure without any further clean-up step. The separation of the analytes was carried out on an Agilent XDB C18 column (50 mm×2.1 mm, 1.8 μm) using the mobile phases of acetonitrile and 5 mmol/L ammonium acetate-0.1% (volume percentage) formic acid aqueous solution with gradient elution. The extract was determined by rapid resolution liquid chromatography-tandem mass spectrometry. Matrix-matched calibration was used for the quantification. The proposed method showed good linear correlation with the correlation coefficients all above 0.98. The blank samples were fortified at three levels, and the recoveries ranged from 77.6% to 105.7% with the RSDs from 2.5% to 13.7%. The limits of detection ranged from 0.1 μg/kg to 15.8 μg/kg. The developed method was successfully applied for mycotoxin analysis in 41 samples bought from markets. The method shows advantages in both accuracy and sensitivity, and is suitable for the rapid multi-aflatoxin screening in cereal-based complementary foods for infants and young children.
Organophosphorus pesticides (OPs), malathion, methyl parathion, trichlorfon, and acephate were used frequently in vegetable cultivation, mainly metabolized into O,O-dimethyl dithiophosphate, 4-nitrophenol, dimethyl dichloroviny phosphate (DDVP) and methamidophos, respectively. A method of liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the determination of the organophosphorus pesticides and their metabolites. According to the difference of coloring matter contents in vegetable matrix, the pre-treatment for vegetables with high coloring matter contents were performed using activated carbon coupled with a Florisil solid-phase extraction column, and others were purified by a Florisil solid-phase extraction column. A hydrophilic interaction chromatographic column (ACQUITY UPLC BEH HILIC) was used with acetonitrile-5 mmol/L ammonium acetate as mobile phases. The MS/MS detection was performed under positive or negative electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode. The results showed that the matrix effect of the LC-MS/MS was 15.3%-45.1%, the recoveries of the four organophosphorus pesticides and their metabolites were 76.9%-102.8%, the precision ranged from 5.92% to 10.19%, the limits of quantification ranged from 0.001 to 0.01 mg/L, and the linear correlation coefficients were 0.9982-0.9999 in the range of 0.01-1.00 mg/L. This method was applied in the analysis of Chinese cabbages, hot peppers, tomatoes and onions from markets. This method can be applied in rapid detection of the organophosphorus pesticides and their metabolites in vegetables.
A novel analytical method for simultaneous determination of sixteen organic acids by on-line enrichment and ion chromatography-mass spectrometry (IC-MS) was developed. On-line enrichment and separation of the organic acids were performed by ion chromatography on a homemade enrichment column and a homemade separation column. The qualitative and quantitative analyses of the organic acids were performed by mass spectrometry in selected ion monitoring (SIM) mode on the basis of atmospheric pressure chemical ionization (APCI) source in negative mode. The sample of 200 μL was injected for the analysis, and the on-line enrichment time was 3 min. The sodium hydroxide solution was used as a gradient elution system. The two columns made it possible to have a low limit of detection due to the good enrichment and separation capability. The sixteen organic acids were separated completely within 30 min. All curves showed good linearity within the test concentration ranges. The limits of detection (LODs) were between 0.01 and 0.22 mg/L, and the average recoveries were between 70.6% and 110.8%. The relative standard deviations (RSDs) were less than 6.3%. The results indicate that this method is simple, rapid, sensitive and accurate for the determination of the organic acids in feed additives.
An analytical method using ultra-high performance liquid chromatography (UPLC) was developed for qualitative and quantitative analysis of 25 illegally added drugs in diet health foods. The diet food samples were extracted using 40 mL methanol by sonication. After centrifugation, the supernatants were separated on a Waters HSS T3 column with gradient elution at a flow rate of 0.3 mL/min, coupling with diode array detection (DAD) in wavelength range from 200 nm to 400 nm. The binary mobile phase was acetonitrile and 10 mmol/L ammonium acetate solution (containing 0.1% formic acid). The correlation coefficient of standard curve for each drug in linearity range was not less than 0.997, as well as the recoveries of all the drugs in diet health foods were 70.7%-104% with the relative standard deviations (RSDs) of 0.132%-5.03% at three spiked levels. Seventeen diet food samples were tested, in which phenolphthalein was found in three samples and emodin was found in one sample. The method is specific, easy, quick, and suitable for confirmation of the 25 illegally added drugs in diet health foods.
A new method was developed for the determination of pesticide residues in crucian carp using on-line gel permeation chromatography-multi gas chromatography/mass spectrometry (GPC-MDGC/MS). The pesticide residues were extracted with cyclohexane-ethyl acetate (1:1, v/v) for twice. After being frozen, the extract was filtered by 0.22 μm member, and then cleaned up and analyzed by online GPC-MDGC/MS. The pesticides were selectively transferred from the 1st column to the 2nd column by means of heart cutting. As a result, selective transfers of some pesticides from the first to the second dimension were at times essential to avoid overlapping. The selected separation conditions from the study with standards were applied to crucian carp spiked with some pesticide standards. The performance of this method was examined by recovery, linearity and precision. Inter-standard quantitative method was used for calculation. Good linear relationship was achieved in the range of 0.01-0.9 mg/L for the 14 pesticides with correlation coefficients above 0.99. The recoveries of the method ranged from 83.0% to 112.9% with the relative standard deviations (RSDs) among 3.2%-12.0% at 3 spiked levels of 0.01, 0.05 and 0.1 mg/kg. This is a simple, rapid method for the analysis of multiple pesticide residues in crucian carp with high accuracy and sensitivity. The results prove that the employment of a multidimensional analysis technique permits to avoid interferences of the analytes with matrix components.
A gas chromatography-mass spectrometry (GC-MS) method was established for the determination of the residues of three β-agonists (clenbuterol, salbutamol and ractopamine) in pig edible tissues. The matrix effects (MEs) in the analysis of the three compounds with the developed method were determined. The influences of matrix state and its weight on MEs were evaluated statistically. The analytes in pig liver and muscle and their corresponding freeze-dried powders were derivatized with N,O-bis(trimethylsilyl) trifluoroacetamide. Then the derivatives were determined in selected ion monitoring mode and the intensities of MEs of the three β-agonists were obtained. Significant matrix enhancement was observed for the three analytes, and especially, the ME of ractopamine was more than 1000%. The results of analysis of variance (ANOVA) demonstrated that MEs were significantly different for the three analytes in two matrices among different matrix weights (P < 0.05), and MEs of the three analytes increased from 1 g to 5 g with the increase of matrix weight. MEs for the three analytes were not significantly different between fresh pig tissues and its freeze-dried powder matrices (P > 0.05), indicating that the freeze-dried powder matrices might be used to conveniently prepare the matrix-matched calibration solution, which could efficiently compensate the MEs of the β-agonists in GC-MS analysis.
The thermodynamic parameters of ionic liquid 1-hexyl-3-methylimidazolium trifluoromethansulfonate ([HMIM]OTF) were investigated by inverse gas chromatography in the temperature range of 343.15-373.15 K. Eighteen probe solvents were used to calculate the molar enthalpy of sorption, molar enthalpy of mixing at infinite dilution, molar enthalpy of vaporization and the mass fraction activity coefficients. Furthermore, Flory-Huggins interaction parameters, the solubility parameter of the ionic liquid were calculated to judge the interactions between [HMIM]OTF and the 18 probes solvents. The results showed that among the selected solvents, n-C6-9, tetrahydrofuran, diethyl ether, cyclohexane and benzene are the poor solvents for [HMIM]OTF, while dichloromethane, acetone, chloroform, ethyl acetate, carbon tetrachloride, methyl acetate, toluene and methanol are the favorite solvents for [HMIM]OTF. In addition, the solubility parameter of [HMIM]OTF at room temperature (298.15 K), which was obtained by linear extrapolation method, was 20.74 (J/cm3)0.5. This study could be used as a reference to the application and research of the ionic liquids.
An analytical method using liquid chromatography with inductively coupled plasma mass spectrometry (LC-ICP-MS) for the determination of trivalent chromium (Cr(Ⅲ)) and hexavalent chromium (Cr(Ⅵ)) in dried edible fungi was established. Edible fungi sample was ashed by a microwave ashing system and Na2EDTA was added to the ashing sample to stabilize the Cr(Ⅲ). An anion exchange column (250 mm×4.6 mm, 10 μm) with a 60 mmol/L nitric acid (pH 9.3) solution as mobile phase was used for the separation and using ICP-MS as a detector for the determination of trivalent chromium and hexavalent chromium. The calibration curves were linear in the range of 0.5-50 μg/L and the correlation coefficients were 0.9999 for Cr(Ⅲ) and Cr(Ⅵ). The average recoveries of Cr(Ⅲ) and Cr(Ⅵ) ranged from 78.0% to 90.7% with the relative standard deviations (RSDs, n=6) less than 4%. The limits of quantification (LOQ) of Cr(Ⅲ) and Cr(Ⅵ) were 0.5 μg/L. The method is efficient, reliable and sensitive, and can meet the requirement for the determination of Cr(Ⅲ) and Cr(Ⅵ) in dried edible fungi.
A method for the determination of ethephon, thidiazuron and diuron in cotton samples has been developed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample was extracted with methanol-water. The separation was carried out on a C8 column (150 mm×4.6 mm, 5 μm) with methanol-water (6:4, v/v) as mobile phase at a flow rate of 0.4 mL/min, and the injection volume was 20 μL. Then the sample solution was analyzed by HPLC-MS/MS in negative ion mode with multiple reaction monitoring (MRM). There were one precursor/two product ion transitions for each pesticide. The results showed that the working curves were linear in the range of 0-10 μg/L for ethephon and thidiazuron, and 0-1 μg/L for diuron. The correlation coefficients (r) were all over 0.999. The limits of quantitation (LOQ) of ethephon, diuron were 40 μg/kg, that of thidiazuron was 4 μg/kg. The average recoveries varied from 89.4% to 100.2% with the relative standard deviations (RSDs) of 5.7%-11.5% at three spiked levels (LOQ, 2LOQ and 4LOQ). The method is simple, rapid and accurate, and can meet the requirements of the domestic and international legislation. The method adapts to confirm the residues of ethephon, thidiazuron and diuron pesticides in cotton samples.
A method was developed for the determination of N-carbamyl-L-glutamic acid (NCG) in feedstuff by high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). The feedstuff samples were extracted with methanol, cleaned-up by a ProElut mixed-mode of strong anion exchange inverse column (PXA). Then the samples were separated with HPLC and detected with MS/MS in multiple reaction monitoring (MRM) mode via positive electrospray ionization (ESI+). The fragment ions of m/z 148.0 and m/z 84.0 were used for qualitative analysis, and m/z 130.0 was selected for quantitative analysis. The limit of detection for NCG was 24 μg/kg (S/N >3), and the limit of quantification was 80 μg/kg (S/N >10). The standard calibration curve was linear over the range of 20-1000 μg/L, and the correlation coefficient was 0.9999. The recoveries of NCG in feedstuff were 104.0%, 103.5%, 95.3%, at the three spiked levels of 80, 200, 500 mg/kg with the relative standard deviations (RSDs) of 7.5%, 6.3% and 5.8%. The results showed that the method is simple, fast, highly sensitive, specific and with good purification effect. It can be applied to the analysis and determination of NCG in feedstuff.
An HPLC method was developed for the determination of methylglyoxal in Manuka honey of New Zealand. The honey sample was dissolved in water and mixed with o-phenylenediamine solution for derivatization. After the reaction for at least 8 h in the dark at room temperature, the solution was filtered with 0.22 μm membrane and injected into an HPLC system for analysis. The separation was carried out on a Kromasil reversed phase column with gradient elution. The mobile phases were methanol and 0.1% (v/v) acetic acid aqueous solution. The detection wavelength was 318 nm. The external standard method was used for quantitation. The linear range of methylglyoxal was 1-50 mg/L with a correlation coefficient of 0.9999. The LOD (S/N=3) and LOQ (S/N=10) were 0.02 mg/L and 0.06 mg/L, respectively. The recoveries at the spiked levels of 50, 100, 200 mg/kg were 98.3%-101.5% and the RSDs (n=5) were less than 5%. The derivative of methylglyoxal was stable within 24 h. The results showed that the pretreatment of this method is simple and the sensitivity, the recovery and repeatability are good. This method can be used for the quality control of Manuka honey of New Zealand, and also for the detection of methylglyoxal in Chinese honey.
A method for the determination of diethylstilbestrol (DES), hexestrol (HEX) and dienestrol (DS) residues in drinking water was established by on-line solid phase extraction (SPE) coupled with high performance liquid chromatography (HPLC). The material synthesized on the base of sol-gel technology was employed as adsorbent. This material was prepared using 3-aminopropyltriethoxysilane (APTES) as the functional monomer, tetraethoxysilane (TEOS) as the crosslinking agent, and acetic acid as the initiator. The synthesized adsorbent showed outstanding property for the estrogen extraction. The estrogen can be caught effectively from water samples and the extraction can be achieved rapidly. Some important parameters, such as pH of sample solution, eluent solvents, loading flow rate, which might influence extraction efficiency, were optimized. The results indicated that the limit of detection (S/N=3) of the developed method could reach 0.07-0.13 μg/L under the conditions of pH 7.0 of sample solution, methanol and 1% (v/v) acetic acid aqueous solution as the eluent solvent and the loading flow rate of 2 mL/min. The recoveries of the three estrogens from the water samples at three spiked levels ranged from 82.31% to 99.43% with RSD of 1.61%-7.15%. The method was simple, rapid, and suitable to detect the trace residues of estrogens in drinking water.
Eight mandelic acid compounds were enantioseparated with amylose-based chiral stationary phase Chiralcel OJ-H and cellulose-based chiral stationary phase Chiralpak AD-H, in the normal-phase mode. It showed that Chiralcel OJ-H exhibited higher enantioseparation, and the eight mandelic acid compounds can be baseline separated in 36 min by Chiralcel OJ-H. Also, the substituents in the aromatic ring of mandelic acid compounds have great influence on the degree of difficulty in the resolution of mandelic acids. The negative inductive effect will reduce the retention time of the mandelic acid compounds on the stationary phase while the positive inductive effect will increase the retention time of the mandelic acid compounds. The steric hindrance effect of the substituents is the key factor influencing the success or failure of the resolution. The possible mechanism of chiral recognition is discussed by comparison and analysis of the differences in their structures. Many factors contribute to enantioseparation of the mandelic acids, including the hydrogen bonds, dipole-dipole interactions, π-π interactions and spatial adaptability between chiral stationary phases and the mandelic acids. Among them, the spatial adaptability plays a crucial role in the resolution of the mandelic acids. This study provides a reference for the enantiomeric purity determination and resolution of some practical optically active mandelic acid and its analogs.
A method for the determination of C1-C6 organic acids in the products from syngas to olefins (SGTO) was developed by ion chromatography, which included the optimized separation conditions, the linear ranges and the working curves determined by using standard samples, the precision and accuracy of the method and the alkaline-washing conditions of the pretreatment for the oil phase samples. The SGTO water phase and oil phase samples were analyzed according to the method. The linearity test showed that the correlation coefficients (R2) for all of the C1-C6 organic acids in the specific concentration ranges were above 0.99, which means that all the components had good linear correlations. The recoveries of standard solutions were from 95.6% to 104.3%, and the RSDs (n=5) were from 0.4% to 3.6%. The spiked recoveries in SGTO oil phase samples were from 91.1% to 96.8%, and the RSDs (n=5) were from 0.7% to 2.3%. The accuracy of the method can satisfy the requirement for the analysis of SGTO samples. The results showed that there were more C2-C4 organic acids in the water phase samples, while there were more C4-C6 organic acids in the oil phase samples. This research has great significance for the study of SGTO reaction, the improvements of catalysts and operation conditions, and is helpful for choosing the materials of the equipment.
byDalian Institute of Chemical
Physics,CASNational Chromatographic R. and A.
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