查看更多>>摘要：? 2022In this work, a porous extended network covalent organic framework designated as TP-NDA-COF was synthesized by the reaction of 2,4,6-trihydroxy-benzene-1,3,5-tricarbaldehyde (TP) and 1,5-naphthalenediamine (NDA). The structure and morphology of the TP-NDA-COF was characterized by means of Fourier transform infrared spectra (FT-IR), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscope (SEM). The TP-NDA-COF was applied as a solid-phase extraction adsorbent for the extraction of some chlorophenols from water and lemon black tea beverage samples prior to high performance liquid chromatography-UV detection. The main experimental parameters that affect the extraction efficiency including the type and volume of eluent, sample solution volume, sample loading rate and sample solution pH were investigated. Under the optimal conditions, the calibration curves were linear in the range of 0.30–60.0 ng mL?1 with the determination coefficients (R2) of 0.9996–0.9998 for water samples and in the range of 0.60–60.0 ng mL?1 with the R2 values from 0.9990 to 0.9996 for beverage samples. At the signal to noise ratio of 3 (S/N = 3), the method LODs for the analytes were 0.10–0.15 ng mL?1 for water samples and 0.20–0.50 ng mL?1 for lemon black tea beverage, respectively. Good repeatability was achieved with the relative standard deviations of less than 7%. The results showed that the SPE-HPLC method can be used for the determination of chlorophenols in environmental water and foodstuffs samples.
查看更多>>摘要：? 2022Separation of isomers is important in diverse areas such as life science, chemical industry, pharmaceutical and environmental science, but still challenging due to their similar physicochemical properties. Development of new stationary phases is an effective way to improve the performance of chromatography for the separation of isomers. Here, we report the post-modification of a new hydroxyl-functionalized covalent organic framework (COF) TzDHNDA with [(1-phenylethyl)amino]acetic acid (PEAA) via esterification reaction to construct PEAA functionalized COF (TzDHNDA-PEAA). The prepared TzDHNDA-PEAA was stable up to 380 °C and used as stationary phase to make TzDHNDA-PEAA coated capillary column for gas chromatographic separation of isomers. The TzDHNDA-PEAA coated capillary column showed a high column efficiency for n-dodecane (12417 plates m?1, 120 °C) and high resolution separation of the isomers of fluoroaniline (Rm-/o-=3.2, Rp-/m-=2.4), chloroaniline (Rm-/o-=5.7, Rp-/m-=1.8), nitrotoluene (Rp-/o-=2.2, Rm-/p-=1.7), pinene (Rβ-/α-=2.4), ionone (Rβ-/α-=4.8) and 1,3-dichloropropene (RE-/Z-=2.0). The fabricated column offered better separation of chloroaniline isomers than commercial capillary columns InertCap WAX, InertCap 1701 and InertCap 5. The introduced benzene ring, secondary amine and carbonyl groups of PEAA into the COF TzDHNDA significantly improved the resolution of isomers due to the enhanced hydrogen-bonding and π-π interactions. This work shows that post-modification strategy is an effective way to prepare novel COFs for chromatographic separation of isomers.
查看更多>>摘要：? 2022The analysis of toxic volatile organic compounds (VOCs) in environmental air is important because toxic VOCs induce adverse effects on human health. Although gas chromatography- mass spectrometry (GC–MS) is the standard instrument for analysis of trace VOCs in air, this mode of analysis requires preconcentration and cryogenic processes. The preconcentration and subsequent thermal desorption of VOCs require special instruments and a long time of processing sample that significantly limit applications of GC–MS for monitoring indoor and outdoor VOC levels. Using a microfabricated preconcentrator for VOC analysis also has the challenge of a large sample volume for concentration. Using solid-phase microextraction (SPME) for VOC analysis by GC–MS often approaches the limit of detection of the GC–MS instrument for trace VOCs in air. This work reports a simple method to integrate microfabricated preconcentrators with commercial SPME fibers in a two-stage concentration processes to achieve rapid and reliable measurement of trace VOCs in air by GC–MS. We designed and fabricated a preconcentrator with micropillars in a microfluidic chamber to support sorbents and to increase the heat transfer rate to the sorbents for rapid thermal desorption. The effects of air flow rates through the preconcentrator on VOCs adsorption and thermal desorption were optimized for increasing analytical accuracy of VOCs measurements. The integration of a micropreconcentrator with SPME enabled measurements of sub-ppb levels of benzene, toluene, ethylbenzene, and xylene (BTEX), and trichloroethylene (TCE) in environmental air by GC–MS.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper enantiomers of selected chiral agrochemicals representing various structural classes were separated by using nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) employing a capillary column packed with silica particles containing immobilized amylose tris(3?chloro-5-methylphenylcarbamate) (i-ADMPC) as a chiral selector (CS). Special attention was paid to peak dispersion in nano-LC and CEC instruments used in order to make comparison between these two techniques more reliable. Enantioseparations were studied utilizing methanol (MeOH) or acetonitrile-water (ACN[sbnd]H2O), both containing 5 mM of ammonium acetate as the mobile phases (MPs). The tested chiral stationary phase (CSP), containing 20% (w/w) of the neutral CS onto native silica, allowed the generation of sufficiently strong electroosmotic flow (EOF) to observe separation of enantiomers of studied agrochemicals in a reasonable time also in CEC mode. Modestly higher efficiencies and enantioresolutions were obtained in CEC than in nano-LC. Just a moderate preference of CEC over nano-LC in this particular study can be explained with a significant mass transfer resistance through the CSP that is caused due to high content of the CS in CSP.
查看更多>>摘要：? 2022We recently published a new concept using monoacylglycerol-like fragments [MG+H-H2O]+ (ions B) produced in-source by atmospheric pressure photoionization in positive mode and high-resolution mass spectrometry for the determination of the fatty acyl (FA) composition of triacylglycerols (TGs) from plant oils. This study extends the concept to the phospholipids (PLs) category and shows that the APCI+ source can also be used. Moreover, the coupling with NP-LC allows to simultaneously analyze different PLs classes in the same sample. We compared the relative intensities of the ions B produced in-source to the % composition of FAs determined by GC-FID. In the case of PLs from natural extracts composed exclusively of diacyl-PLs, the relative intensities of ions B are close to the % of the FAs obtained by GC-FID. This approach is not directly useable for extracts containing plasmalogens (P-PLs). For these PLs, acidic hydrolysis by HCl fumes allows hydrolyzing selectively vinyl ether functions to form lyso-PLs. The analysis of hydrolyzed extracts makes it possible to obtain the composition of P-PLs FAs thanks to the lyso-PLs thus formed, while the diacyl-PLs composition remains unchanged. Unlike GC-FID FAs determination, this approach allows a distinction between the diacyl-PLs and P-PLs FAs composition. We also found that the ion B intensities were consistent among the PL classes (PG, PE, PA, PI, CL, PS and PC) and lyso- forms (LPE and LPC). In the case of the diacyl-PLs extracts analyzed, no statistically significant differences were found between the PLs FAs compositions calculated from ion B intensities and the corresponding GC-FID data. A weighting coefficient was applied to correct ion B intensities issued from polyunsaturated FAs with three or more double bonds. The fatty alkenyls composition of P-PLs could also be calculated from the % intensities of specific ions.
查看更多>>摘要：? 2022 Elsevier B.V.Furfuryl alcohol (FFA) is a furan derivative potentially hazardous to human health, and it is now ubiquitously found in foods and used for identifying singlet oxygen (1O2) in environmental studies. However, current analytical methods for FFA in water are mostly based on gas chromatography and liquid chromatography (LC), which inevitably employ organic solvents as extractants or eluents that can result in harmful wastes production and extra treatment costs. To solve this issue, we herein developed a green analytical method to measure FFA without using organic solvents by a tailored ion chromatography (IC) equipped with ultraviolet (UV) detector. The method demonstrated a calibration curve fitting well (R2 > 0.99) for a wide FFA concentration range (i.e., 0.1 ～ 10.0 mg/L) and a method detection limit (0.031 mg/L) comparable to LC method. The recoveries of FFA dosed into real samples exceeded 86.4% with the relative standard deviations below 2.5%. Next, we examined the property and reactivity of FFA through the method. It was found that FFA's acid-dissociation coefficient (i.e., pKa) was not 9.55, which disagrees with an earlier report. FFA was resistant to 254 nm UV or hydrogen peroxide (H2O2) but vulnerable to H2O2-assisted 254 nm UV or 185 nm vacuum UV, confirming that FFA was sensitive to hydroxyl radicals. Interestingly, FFA was degraded to less extent in water dosed with both sodium hypochlorite (NaOCl) and H2O2 than that dosed with NaOCl only, suggesting that the reaction between NaOCl and H2O2 does not produce 1O2. Given that this IC method can analyze FFA, NaOCl, and H2O2 simultaneously in one run, the evidences presented here may have helped clear a controversy about the 1O2 formation possibility by NaOCl and H2O2.
查看更多>>摘要：? 2022In this paper, a micro gas chromatographic column (μGCC) was fabricated via the layer-by-layer (LBL) deposition of mesoporous silica (MS) as the stationary phase. The μGCC with embedded elliptical-cylindrical posts was fabricated by typical micro-electro-mechanical system (MEMS) techniques. The MS powder was prepared by a sol-gel method and then deposited inside the microchannels of the μGCC by LBL deposition. This process avoided the high temperature required for the sol-gel method to directly prepare MS inside the microchannel surfaces of the μGCC. Mixtures of light alkanes (C1–C4) could be separated in the μGCC. The separation results showed that the resolution between the components of the sample increased with the number of deposition cycles. When the number of deposition cycles increased from 1 to 8, the resolution of methane and ethane was increased from unseparated to 5.89.
查看更多>>摘要：? 2022Knowledge on the presence of occurrence of oxygen containing transformation products (OxyTPs) of the current-use flame retardants hexabromobenzene (HBB), pentabromotoluene (PBT) and pentabromoethylbenzene (PBEB) is limited due to the lack of standard compounds. For this purpose, we investigated the structures of tri- and tetrabrominated phenols, diphenols, methylphenols and ethylphenols. First, 13 non-brominated or partly brominated (alkyl) phenols and diphenols were brominated with the goal to generate all possible tri- and tetrabrominated isomers. Instead of compound isolation and spectroscopic analysis, the resulting products were interpreted by combinatoric evaluation of GC/MS data, data from undirected syntheses and UV transformation studies as well as theoretical considerations. Altogether, all 44 tri- to tetrabrominated OxyTPs existing in theory could be assigned and fed in a data base.
查看更多>>摘要：? 2022 The Author(s)The impact of the two essential parameters, the complexation constant and the mobility of the formed diastereomeric complex, on stereoisomer separation in presence of a neutral chiral selector was assessed by computer simulation for an electrokinetic chromatography configuration with a uniform background electrolyte and one with a cationic discontinues buffer system of isotachophoretic nature. With two enantiomers of norpseudoephedrine as model analytes, data for seven cases featuring complexation in free solution with various combinations of input values, complexation with an immobilized selector and no complexation were analyzed in a hitherto unexplored way. For the uniform buffer study, the determined differences of the effective mobilities and separation selectivities of the stereoisomers were found to be equal to those calculated with the well-known algebraic equations. For the isotachophoretic system with its Kohlrausch adjusted zones, separation is also based on differences in effective mobilities, but the mobility differences cannot be predicted with the same algebraic equation. In both techniques, chiral separations occur due to the presence of the selector and if there is inequality between the mobilities of the transient diastereomeric complexes and the mobility of the free, uncomplexed analyte. Separation of the stereoisomers is possible when complexation constants, complex mobilities or both of these parameters differ. In the isotachophoretic separation a migrating steady-state is formed in which analytes either establish consecutive zones with plateau concentrations or, if present in an insufficient amount, as a peak-like distribution that migrates within a moving steady-state boundary. Simulation data illustrate for the first time the use of a spacer compound that establishes an isotachophoretic zone between enantiomers and thereby provides complete separation of the enantiomers and the possibility of individual detection in peak-mode isotachophoresis. They demonstrate that such an approach could be employed to assess the enantiomeric purity of a chiral compound.
van Bommel M.R.Groeneveld I.Pirok B.W.J.Molenaar S.R.A....
5页
查看更多>>摘要：? 2022 The AuthorsIn cultural heritage the characterization of organic colorants is a challenging task. Currently, different chromatographic techniques are used to analyze natural and synthetic dyes separately, since the classes differ significantly in chemical properties and, therefore, chromatographic behavior. To save time, costs and sample material, we developed a method suitable for a wide variety of organic colorants using ultra-high-performance liquid chromatography coupled to a photo-diode-array detector. Gradient elution was performed with a mobile phase consisting of water and methanol with 5 mM triethylamine added as an ion-pairing agent at a pH of 3. Both linear and step gradients were optimized using the ‘Program for Interpretive Optimization of Two-dimensional Resolution’ (PIOTR) Pirok et al. [22]. Two optimized linear gradients and two step gradients were evaluated experimentally. The method was applied on a complex dye mixture containing nearly 130 natural- and synthetic-dye reference compounds. More than 100 of these compounds could be identified in a single experiment. The feasibility of the method was demonstrated by analyzing samples of several precious objects that were found in the Texel shipwreck Vos et al. [2] and of two embroideries of Emile Bernard, the results of which are described in this paper.
NSTL
Elsevier