查看更多>>摘要：The enantioseparation of four oxazolidinone and one biosimilar thiazolidine derivatives was performed on seven different polysaccharide-type chiral stationary phases (Lux Amylose-1, Lux i-Amylose-1, Lux Amylose-2, Lux Cellulose-1, Lux Cellulose-2, Lux Cellulose-3, Lux Cellulose-4) differing in backbone (cel-lulose or amylose), substituent or the immobilization technologies (coated or immobilized). Polar organic mode was employed using neat methanol (MeOH), ethanol (EtOH), 2-propanol (IPA) and acetonitrile (ACN) either alone or in combinations as mobile phases. Amylose-based columns with ACN provided the highest enantioselectivities for the studied compounds. The replacement of an oxygen with a sulfur atom in the backbone of the studied analytes significantly alters the enantiomer recognition mechanism. Chiral selector-, mobile-phase-, and interestingly immobilization-dependent enantiomer elution order re-versal was also observed. Reversal of elution order and hysteresis of retention and enantioselectivity was further investigated using different mixtures of IPA:MeOH and ACN:MeOH on amylose-type chiral station-ary phases. Hysteresis of retention and enantioselectivity was observed on all investigated amylose-type columns and binary eluent mixtures, which can be further utilized for fine-tuning chiral separation per-formance of the studied columns. (c) 2021 Elsevier B.V. All rights reserved.
Sakallioglu, Isin T.Maroli, Amith S.Leite, Aline De LimaPowers, Robert...
14页
查看更多>>摘要：A rapid reversed-phase ultra-high-performance liquid chromatography-high resolution mass spectrometry based mycobacterial lipidomics approach is described. This method enables the separation of various lipid classes including lipids specific to mycobacterial, such as methoxy mycolic acid and alpha-mycolic acid. Lipid separation occurs during a relatively short runtime of 14 min on a charged surface hybrid C-18 column. A high-resolution quadrupole-time of flight mass spectrometer and a data independent acquisition mode allowed for the simultaneous acquisition of the full scan and collision induced dissociation fragmentation. The proposed method provides lipid detection results equivalent to or better than existing methods, but with a faster throughput and an overall higher sensitivity. The reversed-phase ultra-high-performance liquid chromatography-high resolution mass spectrometry method was shown to obtain structural information for lipids extracted from Mycobacterium smegrnatis, but the method is applicable to the analysis of lipids from various bacterial and mammalian cell lines. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Ultraviolet (UV) light-catalyzed Paterno-Buchi (PB) reaction has been developed as an efficient lipid C=C double bond (DB) derivatization strategy, which can accurately assign the position of C=C bond in unsaturated lipids when coupled with tandem mass spectrometry (MS/MS). Inspired by this, here we proposed a novel visible-light induced [2+2] cycloaddition reaction combined with ESI-MS/MS and MALDI-MS/MS to identify lipid C=C position isomers. Benz[g]isoquinoline-5,10-dione (BIQD) and 6,9-difluorobenzo[g]isoquinoline-5,10-dione (DF-BIQD) were developed as a new type of [2+2] cycloaddition reagent, which can not only react with C=C bond under 254 nm UV light irradiation, but also quickly combine with lipid C=C bond under the irradiation of 405 nm visible-light and > 400 nm compact fluorescent lamp visible-light. High cycloaddition reaction conversion efficiency can be achieved by irradiating under compact fluorescent lamp light for 2 min. Moreover, we discovered that 437 nm, 489 nm, 545 nm, 581 nm, and 613 nm monochromatic light appearing in compact fluorescent lamp can individually induce the [2 + 2] cycloaddition reaction between DF-BIQD and unsaturated lipids. Using this method, we found that the expressions of lipid DB-positional isomers in rat heart, brain, lung, spleen, thymus, kidney, liver and plasma vary greatly. The relative content of FA-18:1 (Delta 9) in rat heart is only 1.49 times that of FA-18:1 (Delta 11), while the relative content of FA-18:1 (Delta 9) in rat plasma is 5.20 times that of FA-18:1 (Delta 11). The above results offer new insight into the development of photocatalytic reagent for visible-light induced [2+2] cycloaddition and structural lipidomic studies. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Comonomer content distribution (CCD), also commonly known as chemical composition distribution (CCD) and short chain branching distribution (SCBD), describes the variation of short chain branching composition between individual polymer chains in polyolefin materials. It is of particular importance for controlling polyolefin performance. Crystallization-based separation methods have evolved over the past four decades aiming at resolution, speed, precision, and accuracy. Two of the commonly used techniques are Crystallization Elution Fractionation (CEF) and Temperature Rising Elution Fractionation (TREF), where polymer chains are physically separated along the column or on the surface of the support based on their crystallinity, respectively. CEF analysis takes much less time than TREF. There is a critical need for precise temperature calibrations for data repeatability. This report demonstrates a novel CEF methodology using a two-point technique to consistently and conveniently calibrate the comonomer composition and column temperature. This column temperature calibration methodology was adopted in a study by tracking the reproducibility over a period of 8 years, using multiple instruments located in different laboratories and in different geographies. The results exhibited superior repeatability, with less than 0.3% of the relative error calculated from 3000 data points of the eluting peak temperature, thus demonstrating this as a robust method for industrial labs that require good quality controls. (C) 2021 Elsevier B.V. All rights reserved.
Bian, JuanGirotti, JamesFan, YuchenLevy, Elizabeth S....
8页
查看更多>>摘要：Liposomes are an attractive drug delivery platform for a wide variety of pharmaceutical molecules. Encapsulation efficiency, which refers to the amount of drug contained inside liposomes compared with the total amount of drug, is a critical quality attribute of liposome products, as the free drug in a liposomal formulation may cause toxicity or undesired biodistribution. The determination of encapsulation efficiency requires the measurement of at least two of the three drug populations: total drug, encapsulated drug and free drug. However, direct measurement of the encapsulated drug and free drug remains a challenging analytical task. Nanoparticle exclusion chromatography (nPEC), an emerging high-performance liquid chromatography (HPLC) technique, has shown great potential in separating and quantifying the free drug in liposomal formulations. In this study, nPEC was systematically evaluated for two representative liposomal formulations containing either hydrophilic or hydrophobic small molecule drugs. It is reported for the first time that the insoluble free drug suspended in the aqueous formulation can be directly measured by nPEC. This free drug in the suspension sample was quantified with excellent accuracy and precision. On the other hand, the total drug measurement from dissociated liposomes was confirmed by the benchmark methodology of reversed phase liquid chromatography (RPLC). The facile quantitation of free and total drug in the liposome formulation enables the fast and accurate determination of the encapsulation efficiency, which can be used to guide the formulation development and characterize the product quality. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Multi-template imprinting is one of the challenge for molecular imprinting since the selectivity and binding affinity for each analyte decrease significantly compared with the corresponding molecularly imprinting polymers (MIPs) against single template. In this work, molecular crowding effect was tried to remedy the problem of imprinting reduction caused by the competition of two templates. Methacrylic acid (ACR) was used as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and polystyrene (PS) as macromolecular crowding agent. With levofloxacin ( S-OFX) as the first template, a number of compounds with varied chemical structure were chosen as the second template to investigate the imprinting effect of dual-template. When S-OFX and naproxen ( S-NAP) was used as the dual-template, the imprinting factor (IF) of the resulting MIP for S-OFX was 20.1 and IF for S-NAP was 10.9. In contrast, for the single-template MIPs, IF for S-OFX was 22.4, and IF for S-NAP was 11.9. As a comparison, the IF of the DT-MIP prepared in absence of PS was only 2.3 for S-OFX and 1.0 for S-NAP. To analyze recognition mechanism of the molecular crowding-based imprinting system, molecular dynamics simulations to the chain structure of PS and binding modes between template and functional monomers was conducted by NAMD software. All the results displayed that molecular crowding is a promising method to improve the affinity of the dual-template imprinted polymer. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Column length (L) is a measure of solvent consumption in LC analysis. In its latter role, L is the specific solvent consumption - the void time (t(M)) solvent consumption per unit of the column flow area (A(F)) which is the cross-sectional area of the column open space (external and internal pores). In t(anal)-long LC analysis (isocratic or gradient), the solvent consumption (V-S) is V-S = A(F)Lt(anal)/t(M) regardless of flow rate (F) as long as all changes in column dimensions and operational parameters are translatable (in gradient analysis, the ratio of the gradient time (t(G)) to t(M) remains fixed). (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：This paper represents the results of a case study investigating the development of a novel, simple, costeffective, solventless and sensitive chromatographic method for the determination of volatile pesticides in aqueous samples by an electrothermally prepared pencil graphite (PG). In this study, PG were conditioned by passing a suitable direct current to activate PG by Joule effect. Conditioned PG was used for the extraction of Chlorpyrifos (CP), which is used as case study. The method was also found successful in the determination of CP in real water samples, providing acceptable recovery values (82-111%). (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, novel cyclodextrin-dendrimers nanocomposites functionalized high performance liquid chromatography stationary phases were developed for efficient separation of aromatic compounds. beta-cyclodextrin was grafted onto the surface of silica gel matrix with poly (amidoamine) dendrimers as spacers. Scanning electron microscope, fourier transform infrared spectroscopy, element analysis and Brunner-Emmet-Teller measurement proved the successful grafting of cyclodextrin-dendrimers nanocomposites. The obtained stationary phases showed satisfactory separation effects for alkylbenzenes and benzenesulfonic acid substituents in reverse phase liquid chromatography mode. Weak hydrophilic and ion exchange interactions were also confirmed at the same time. Meanwhile, the effects of dendrimers and cyclodextrin on the chromatography performance were discussed. Separation mechanism of the stationary phases were verified by two-dimensional nuclear magnetic resonance technology, and the result implied that the proposed cyclodextrin-dendrimers nanocomposites functionalized stationary phases have significant prospects for separation and determination of more aromatic compounds in future. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, a novel sorbent, based on UVM-7 mesoporous silica doped with Au, has been proposed for organochlorine pesticides extraction. Cartridges containing this material have been applied to the preconcentration of 20 pesticides from water samples, through a solid-phase extraction (SPE) protocol, with their later determination by gas chromatography with an electron capture detector. First, UVM-7 materials were properly characterized by X-ray diffraction, N-2 adsorption-desorption, electron microscopy techniques, and UV-Vis spectroscopy, thus confirming their structure and Au incorporation. After optimization of main extraction parameters, recoveries in the range of 80-110% were obtained for most of the analytes, with enrichment factors comprised between 275 and 430. The obtained sensitivity was comparable with other reported methods, with limits of quantification in the range of 0.3-20 ng L-1, thus allowing the determination of these compounds according to European legislation. The developed method has been successfully applied to the analysis of real spiked samples in comparison with a reference method, thus being this sorbent an alternative for organochlorine pesticide enrichment, through a simple, reusable, cheap, and environmentally friendly SPE procedure. (C) 2021 Elsevier B.V. All rights reserved.
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