High Separation Ability Research Articles

Effect of blend ratio and coagulation bath temperature on the morphology, tensile strength and performance of cellulose acetate/poly(butylene succinate) membranes

In the present study, blend membranes of cellulose acetate (CA)/poly(butylene succinate) (PBS) were prepared. The membrane morphology, tensile strength and performance in bread wastewater treatment were evaluated in terms of the membrane preparation conditions. According to the results, presence of PBS varied the membrane structure by reducing the extension of macro pores in the membrane sublayer. CA could effectively improve tensile strength of the membranes. Reducing coagulation bath temperature resulted in obtaining the membranes with denser structure and also higher tensile strength. Considering differences in surface and cross-sectional structures, the membranes with PBS content of 85 and 100% were found to have the highest separation ability, whereas the highest flux belonged to the membrane with 50% PBS.

High CO2/N2/O2/CO separation in a chemically robust porous coordination polymer with low binding energy

Porous coordination polymers (PCPs), constructed from organic linkers and metal ions, can provide special pore environments for selective CO2 capture. Although many PCPs have been reported, a rational design for identifying PCPs that adsorb CO2 molecules with a low binding energy, high separation ability and high chemical stability remains a great challenge. Here, we propose and validate, experimentally and computationally, a new PCP, [La(BTN)DMF]·guest (PCP-1⊃guest), that has a large aromatic organic surface and a low binding energy for high CO2 separation from four-gas mixtures (CO2–N2–O2–CO) at ambient temperature. In addition, it shows good water and chemical stability; in particular, it is stable from pH = 2 to 12 at 100 °C, which is unprecedented for carboxylate-based PCPs.

Chromatographic study on the high performance separation ability of a homochiral [Cu2(d-Cam)2(4,4′-bpy)]n based-column by using racemates and positional isomers as test probes

This study focused on exploring the chromatographic characteristic of a homochiral MOF [Cu2(d-Cam)2(4,4′-bpy)]n with 3-D six-connected self-penetrating architectures for the separations of positional isomers and chiral compounds. Some effects such as mobile phase composition, column temperature, and analytes mass for separations on this chiral column also have been investigated. Among thirteen tested racemates, six compounds, namely three alcohols, a diol, a naphthol and a ketone were successfully discriminated, and ten useful positional isomers which have never been separated on other MOFs stationary phases in HPLC except dichlorobenzene and cresol isomers, were also analyzed by this chiral stationary phase. The results indicated that [Cu2(d-Cam)2(4,4′-bpy)]n exhibited good selectivity for positional isomers and enantiomers. Therefore, it is practicable that the separation of positional isomers and enantiomers are carried out on the chiral MOF column.

Studies on Toxicity Effect of Solvents on Growth of Saccharomyces cerevisiae (NCIM 3186)

The present study was conducted to determine the tolerance level of the yeast strain Saccharomyces cerevisiae (NCIM 3186) towards a few selected organic solvents, viz. ethyl oleate, ethyl benzene, ethyl caprylate and decanol (decyl alcohol). The objective of the investigation was to search for a suitable solvent with low toxicity level on yeast cells yet having high separation ability so that it can be used for simultaneous fermentation and extraction of ethanol in a future study. The result shows that ethyl oleate can be regarded as the best suited solvent in comparison to other solvents studied in the present investigation. The order of preference of a solvent which may be used for extractive fermentation is: ethyl oleate > ethyl benzene > ethyl caprylate > decanol (decyl alcohol).

Molecularly imprinted polymers for selective separation of acetaminophen and aspirin by using supercritical fluid technology

In this study, we synthesize molecularly imprinted polymers (MIPs) by using supercritical fluid technology in carbon dioxide (CO2). To prepare MIPs, methyl methacrylate (MMA) is used as a third monomer, methacrylic acid (MAA) or 4-vinylpyridine (4-VP) as functional monomers, acetaminophen (AAP) and aspirin (AS) as templates, and ethylene glycol dimethacrylate (EGDMA) as a crosslinker. To evaluate the binding characteristics of MIPs for AAP and AS, equilibrium binding experiments are conducted. The results indicate that the adsorption equilibrium time is about 120min, and the binding amount increases with the concentration of templates. The adsorption ability of the MIPs is also investigated by performing an HPLC analysis, measuring the adsorbed amounts for templates and their structural analogue, the selectivity factor (α), and the imprinting-induced promotion of binding (IPB). The results of the evaluation analysis indicate that the prepared MIPs have high separation abilities and selectivity. In addition, the molecular recognition properties according to the kind of functional monomers (MAA and 4-VP) and polymerization methods indicate that the use of 4-VP as a functional monomer is more efficient for binding yield and affinity, and the MIPs prepared by using supercritical fluid assisted polymerization are more efficient way to selectively separate and detect templates than bulk and emulsion polymerization process.

Transport Characteristics of Aromatic Acids in the Capillary Electrochromatography with Mixed Magnetic Nanoparticles Coating as Stationary Phase

In this paper, novel open-tubular electrochromatographic system with core/shell magnetic nanoparticles modified by amino and C18 functional groups as mixed stationary phase by using a series of permanent magnets to immobilize nanoparticles into the capillary were investigated. The new system showed high separation ability and efficiency due to high specific surface area of nanomaterial and mixing separation mechanism. The transport equations of aromatic acids using the open-tubular electrochromatographic column with magnetic nanoparticle coating as stationary phases were derived under isocratic and double stepwise gradient elutions, and the retention characteristics of organic acids separated by the columns were further investigated. The results showed that the electroosmotic flow gradually decreased with the increase of Fe3O4@SiO2-NH2 in the mixed stationary phases, and the direction of electroosmotic flow reversed eventually. The capacity factor was relevant to the ratio of ion-exchange and reversed-phase stationary phases. Furthermore, experiments confirmed that the capacity factor of solute had a good linear relationship with the ratio of mixed stationary phases, and the correlation coefficient was greater than 0.9166 after fitting. Under the double stepwise gradient elution condition, the migration time of solute can be predicted by its elution time under isocratic elution. After the solutes were eluted by phosphate buffer stepwise gradient elution, the relative errors between predicted retention time and actual retention time of solute were less than 8.0%. After they were eluted by organic modifier concentration stepwise gradient elution, the relative errors between two values of solute were less than 10%. After they were eluted by pH value stepwise gradient elution, the relative errors between two val- ues of solute were less than 5.8%. Rhizoma gastrodiae was separated by the constructed system under the optimized chroma- tographic condition, the main components of gastrodin, vanilla alcohol and citric acid were identified based on retention time of standards, and the relative errors between predicted value and actual value of citric acid was 11%. The open-tubular elec- trochromatographic system shows great potential in the method development of analysis of complicated samples. Keywords gradient elution; transport characteristic; mixed stationary phase 1 引言

Study of the electrical connection mechanism of sheathless interface for capillary electrophoresis‐electrospray ionization‐mass spectrometry

With the combination of high separation ability of capillary electrophoresis (CE) and strong identification ability of mass spectrometry (MS), CE/MS is becoming a powerful tool for polar and ionic analytes analysis. Different interfaces have been developed to enhance the sensitivity and reliability since the first introduction of CE/MS in 1987. A sheathless porous interface based on a new ions transferring electric connection technique was reported to be with high sensitivity and reliability. In this work, a series of optical and electrochemical experiments were designed to study the electric connection process. The results indicated that closing CE electrical circuit and applying MS spray voltage were achieved by the small ions transferring through the interface porous wall. The new electric connection method significantly enhanced the sensitivity, resolution and stability of the CE/MS analysis. The interface was applied in CE/MS detection of morphine and 6-monoacetylmorphine in urine sample and showed an equal sensitivity to LC/MS. With the significant improvement of sensitivity and stability, the CE/MS with the new interface showed strong potential for the determination of low abundance analytes.

Highly Selective Sorption and Separation of CO2 from a Gas Mixture of CO2 and CH4 at Room Temperature by a Zeolitic Organic–Inorganic Ionic Crystal and Investigation of the Interaction with CO2

Mixed gas cosorption and gas chromatographic investigations demonstrate that a zeolitic organic–inorganic ionic crystal K2[Cr3O(OOCH)6(4-etpy)3]2[α-SiW12O40]·2H2O [1·2H2O] (etpy = ethylpyridine) with a pore diameter of 3.5 A possesses high separation ability of carbon dioxide (kinetic diameter 3.3 A) over methane (3.76 A) at room temperature in the presence of water vapor. Monte Carlo simulation combined with density functional theory calculation suggests that carbon dioxide molecules diffuse into the one-dimensional channels and interact initially with the potassium ions and then with the oxygen atoms of silicododecatungstates, which are confirmed with carbon dioxide sorption enthalpy and in situ IR spectroscopy.

Reduced graphene oxide/CdS for efficiently photocatalystic degradation of methylene blue

Reduced graphene oxide/cadmium sulfide (RGO/CdS) hybrid material was synthesized by a one-step solvothermal method, wherein graphene oxide (GO) was a supporting material on which CdS nanoparticles were distributed homogeneously, and cadmium acetate (Cd(Ac)2·2H2O) was used as the CdS precursor. The supporting material RGO for CdS nanoparticles effectively enhanced their photocatalytic activities for the photodegradation of methylene blue in the aqueous solution. The optimum weight ratio of the GO to CdS in the hybrid material was 5.0%, which exhibited an excellent photodegradation efficiency (94%) and a better removal efficiency of total organic carbon (TOC) (57%), about 2.5 times and 5.1 times higher than that of pure CdS nanoparticles, respectively, under visible light (VL) irradiation. This improved photodegradation efficiency could be attributed to the increased adsorbability for methylene blue molecules, light absorption levels located in visible region, high charge transfer and separation ability, due to the introduction of a two-dimensional RGO network.

Molecular-shape selective high-performance liquid chromatography: Stabilization effect of polymer main chain by alternating copolymerization

This work aims to clarify that stabilization or increased rigidity of polymer main chains as an organic stationary phase can lead the selectivity enhancement in high-performance liquid chromatography (HPLC). For this purpose, the alternating copolymer of octadecyl acrylate (ODA) with a cyclic monomer (N-octadecylmaleimide, OMI) as a rigid segment was synthesized and compared with the ODA homopolymer. Both of the polymer-grafted silicas (Sil-poly(ODA-alt-OMI) and Sil-poly(ODA), respectively) were prepared by radical polymerization on 3-mercaptopropyltrimethoxysilane-modified silica. The characterizations were carried out by elemental analyses, diffuse reflectance infrared Fourier transform (DRIFT), and solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS-NMR) spectroscopies. Chromatographic behaviors were evaluated by the retention studies of shape-constrained isomers of polycyclic aromatic hydrocarbons (PAHs), isomers of tocopherol and carotenoids. Higher molecular-linearity selectivity toward PAHs was obtained on Sil-poy(ODA-alt-OMI) regardless of temperature changes but at temperature below 40°C, Sil-poly(ODA) showed better planarity selectivity than that of Sil-poy(ODA-alt-OMI). As a result, the higher separation ability toward tocopherols and carotenoids was obtained on Sil-poy(ODA-alt-OMI). These results indicate that the stabilization in the polymer main chain by alternating copolymerization and the stabilization in the side chains by a disordered-to-ordered phase transition were effective to enhance the molecular-shape selectivity.

Novel Approach for the Separation of Shape-Constrained Isomers with Alternating Copolymer-Grafted Silica in Reversed-Phase Liquid Chromatography

This paper describes a novel packing material for high selective reversed-phase high-performance liquid chromatography (RP-HPLC). The organic phase on silica is chemically designed in a way that the weak interaction sites are integrated with high orientation along the polymer main chain and high selectivity can be realized by multiple interactions with solutes. For the above purpose, we synthesized poly(octadecyl acrylate-alt-N-octadecylmaleimide)-grafted silica (Sil-poly(ODA-alt-OMI)) stationary phase. The alternating copolymerization was carried out from 3-marcaptopropyltrimethoxysilane (MPS)-modified silica via surface-initiated radical-chain transfer reaction. Elemental analysis, diffuse reflectance infrared Fourier transform (DRIFT),(1)H NMR, solid-state (13)C cross polarization magic angle spinning (CP/MAS) NMR, and suspended-state (1)H NMR were used to characterize the new organic phase. Aspects of shape selectivity was evaluated with Standard Reference Material (SRM 869b), Column Selectivity Test Mixture for Liquid Chromatography. Enhanced molecular shape selectivity was observed, that lead to the separation of SRM 1647e (16 polycyclic aromatic hydrocarbons, PAHs) in an isocratic elution. The effectiveness of this phase was also demonstrated by the separation of several beta-carotene and tocopherol isomers. The complete baseline separation of the tocopherol isomers was achieved using the Sil-poly(ODA-alt-OMI) phase. Chromatographic study revealed that Sil-poly(ODA-alt-OMI) has extremely high separation ability compared to monomeric and polymeric C(18) columns. Higher shape selectivity of the new RP material can be explained by a pi-pi and dipole-dipole interaction mechanism.

Monolithic silica capillary columns with immobilized cellulose tris(3,5‐dimethylphenylcarbamate) for enantiomer separations in CEC

Two types of monolithic silica capillary columns with an immobilized cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) selector were prepared for enantiomer separations in CEC. The monolithic columns were prepared by a sol-gel process in fused-silica capillaries. CDMPC was then either immobilized on a silica monolith through an intermolecular polycondensation of the cellulose derivative containing a triethoxysilyl group, or on a vinylized silica monolith through radical copolymerization of the cellulose derivative, which also contained a vinyl group. IR spectra confirmed the successful immobilization of CDMPC on both columns. Eleven chiral compounds were used to evaluate the enantioselectivity on both column types. Results indicated that the columns obtained via polycondensation had higher separation ability than those obtained via radical polymerization, and that they showed satisfactory run-to-run repeatability and stability. These new techniques thus provide strategies for preparing immobilized polysaccharide-based chiral silica monolithic capillary columns for chiral separations by means of CEC.

Preparation and evaluation of a chiral stationary phase covalently bound with a chiral pseudo-18-crown-6 ether having a phenolic hydroxy group for enantiomer separation of amino compounds

In order to develop a chiral stationary phase (CSP), which has even higher separation ability than the corresponding commercially available crown ether based CSP (OA-8000 having a pseudo-18-crown-6 ether with an OMe group as a selector), chemically bonded type CSP having a phenolic OH group on a crown ring was developed. Normal mobile phases with or without acid additive can be used with this OH type CSP in contrast to the conventional OMe type CSP which has a neutral chiral selector. Enantiomers of 25 out of 27 amino compounds, including 20 amino acids, 5 amino alcohols, and 2 lipophilic amines, were efficiently separated on a column with this CSP. Nine amino compounds out of 27 were separated with better separation factors than the corresponding OMe type CSP. It is noteworthy that the chromatography on this CSP exhibited excellent enantiomer-separations for amines and amino alcohols when triethyl amine was used as an additive in the mobile phase. Comparison of enantiomer separation ability on this OH type of CSP and on the OMe type of CSP and correlation between the enantioselectivity in chiral chromatography and that of the corresponding model compounds in solution imply that the chiral separation arose from chiral recognition in host guest interactions.

Single-step quantitation of DNA in microchip electrophoresis with linear imaging UV detection and fluorescence detection through comigration with a digest

We demonstrate a convenient single-step quantitation technique for double-stranded DNA (dsDNA) fragments in polymerase chain reaction (PCR) products based on microchip capillary electrophoresis (μ-CE)/UV or fluorescence detection. PCR products of polymorphisms on the human Y-chromosome related to spermatogenic failure did not need purification. They were premixed and comigrated with a DNA digest whose concentration was known. Hydroxyethyl cellulose (HEC) dissolved in 5× Tris–borate–EDTA (5× TBE, pH 8.3) was used as a separation matrix in a linear polyacrylamide-coated quartz microchip, while mixed poly(ethyl oxides) (PEOs) of different molar-masses dissolved in 1× TBE (pH 8.3) containing 1 ng/μl ethidium bromide was used as a separation matrix in an uncoated poly(methyl methacrylate) (PMMA) microchip. Elution profiles were monitored under either real-time linear imaging UV detection in the snapshot mode where the total separation time is fixed, or light-emitting diode (LED) confocal fluorescence detection in the finishline mode where solutes migrate over the same separation length. It is found that, in both modes, a linear relation exists between the peak areas ( A) and the multiplication of the digest concentrations ( C) and the fragment sizes ( L) in a DNA restrictive digest. Using the comigration electropherogram of a single-step experiment, the concentrations of PCR products were directly determined using the A versus LC linear relationship. The sole condition to obey is that the chosen digest has different fragment sizes with the PCR products of interest. This condition is easy to obey, because μ-CE owns high separation ability, and many digests are commercially available. The recovery of the technique was between 98 and 105%. The R.S.D. for chip-to-chip concentration measurements was less than 6.0% ( n = 6). Hence, the technique was accurate and reliable for DNA assays.

Comparison of Different Capillary Electrophoresis Modes and HPLC for the Separation of Xanthones

Nine xanthones from a Chinese traditional medicine, Securidaca inappendiculata Hassk, were separated by different capillary electrophoresis (CE) modes, including capillary zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC), microemulsion electrokinetic capillary chromatography (MEEKC), and capillary electrochromatography (CEC). The comparison of separation selectivity and efficiency for xanthones by using these CE methods indicated that different CE modes greatly varied in the separation selectivity and efficiency for xanthones; their advantages and disadvantages are discussed. Moreover, compared with traditional chromatographic methods, e.g., high performance liquid chromatography (HPLC), CE shows higher separation ability and analytical speed for these xanthones.

Separation of trivalent americium and europium by purified Cyanex 301 immobilized in macro porous polymer

The present work confirms the high separation ability of purified Cyanex 301 towards trivalent americium over europium in liquid-liquid extraction. Solvent 2-nitrophenyl octyl ether (NPOE) lowered the partitioning of Am3+ but remained the separation ability over europium. Solvent toluene and 3-octanone lowered the separation factor to ‐1000. It is feasible to separate Am3+ from Eu3+ by Cyanex 301 which was immobilized in the macro porous polymer (MPP). 3-Octanone is a suitable solvent for dissolving NH4OH-saponified Cyanex 301 and MPP is a suitable solid supported material for column operation. A five-step column experiment demonstrated the feasibility to separate Am3+ from Eu3+ in column which was packed with Cyanex 301-impregnated MPP.

Bi-Functional Organophosphorus Extractants and Computational Modeling for Copper(II) and Zinc(II) Extraction.

Novel bi-functional extractants, which possess two phosphonic groups on both sides of the extractants, have been synthesized for the separation of Zn(II) and Cu(II). The separation properties and extractability of the novel extractants were investigated using the liquid-liquid extraction technique. These bi-functional extractants provide a high selectivity towards Zn(II) over Cu(II) compared to that of monoacidic phosphorus extractant as an analog. We discussed the extraction behavior of the bi-functional extractants with a computational modeling by means of semi-empirical molecular orbital methods. The calculation suggests that the length of the spacer is one of the decisive factors to enhance the selectivity in the bi-functional extractants. The high separation ability for the bi-functional extractants was related to the high energy difference in the heat of formation calculated by computational modeling. The computational simulation was found to be very useful for the design of novel extractants and prediction of their separation performance.

Syntheses of a Series of Fluorescent Carboxylic Acids with a 1,3-Benzodioxole Skeleton and Their Evaluation as Chiral Derivatizing Reagents

A series of fluorescent carboxylic acids with a common skeleton of 1,3-benzodioxole-4- or 5-carboxylic acid were prepared as racemates or in an optically active form. Their potential as chiral derivatizing agents was evaluated in terms of the HPLC and 1H-NMR analyses of D,L-amino acids. Every acid with a carboxyl group at C-4 showed high separation ability of original enantiomers in both the HPLC and the NMR analyses, while the C-5 isomer showed little separation. As the difference in the bulkiness between the two substituents at C-2 became wider, the separation by HPLC increased. These studies allowed us to develop new chiral reagents useful both for HPLC and 1H-NMR analyses, along with our previous reagent, (S)-TBMB carboxylic acid.