Potential of formamide and N-methylformamide in nonaqueous capillary electrophoresis coupled to electrospray ionization mass spectrometry. Application to the analysis of beta-blockers

A nonaqueous capillary electrophoresis (NACE) method, coupled with either UV or electrospray mass spectrometry (ESI-MS), is described for the simultaneous analysis of seven beta-blockers. The same electrolyte, namely 25 mM ammonium formate and 1 M formic acid, was used with different investigated organic solvents. In addition to frequently used organic solvents such as methanol (MeOH) and acetonitrile (MeCN), formamide and its derivatives were investigated. Formamide (FA) and N-methylformamide (NMF) present several interesting physico-chemical properties, one of them being a high dielectric constant (e). Since FA and NMF possess a high UV cutoff, beta-blockers with an absorbance above 250 nm were selected as model compounds in order to compare NACE-UV and NACE-MS performances. FA and NMF showed different selectivity compared to water, MeOH or MeCN, and also demonstrated a higher efficiency in terms of the number of theoretical plates (especially NMF). To overcome their unfavorable optical properties, hyphenation with MS detection appears as a promising technique, thanks to its benefits in terms of selectivity, sensitivity and universality. The practical compatibility of FA and NMF with ESI-MS detection in combination with a sheath liquid configuration was demonstrated. In comparison to UV detection, sensitivity was increased, while a high efficiency was maintained. In addition, the low and stable generated currents observed were evidences for the successful hyphenation with ESI-MS. Hence, FA and NMF seemed to be promising alternatives in NACE-ESI-MS, either used as pure organic solvent or as a mixture with MeOH or MeCN.     

Separation of oligonucleotides in N-methyl-formamide-based polymer matrices by capillary electrophoresis

N-Methylformamide (NMF)-based matrices for capillary electrophoretic separation of nucleic acids have been developed. The use of an organic solvent as liquid base for the separation matrices allowed a hydrophobic polymer, C16-derivatized 2-hydroxyethyl cellulose (HEC), to be employed as structural element in the sieving medium. With a matrix consisting of 5% w/v of this polymer dissolved in NMF containing 50 mM ammonium acetate, p(dA)12-18 and p(dA)40-60 oligonucleotides were baseline separated. The addition of ammonium acetate to the buffer and separation matrix resulted in enhanced separation efficiency. Furthermore, it was possible to tailor the sieving performance of the separation medium by the use of a binary mixture of C16-derivatized HEC and PVP. Differences in sieving behavior of the various matrices evaluated are discussed.     

Amide-induced phase separation of hexafluoroisopropanol-water mixtures depending on the hydrophobicity of amides

Amide-induced phase separation of hexafluoro-2-propanol (HFIP)-water mixtures has been investigated to elucidate solvation properties of the mixtures by means of small-angle neutron scattering (SANS), (1)H and (13)C NMR, and molecular dynamics (MD) simulation. The amides included N-methylformamide (NMF), N-methylacetamide (NMA), and N-methylpropionamide (NMP). The phase diagrams of amide-HFIP-water ternary systems at 298 K showed that phase separation occurs in a closed-loop area of compositions as well as an N,N-dimethylformamide (DMF) system previously reported. The phase separation area becomes wider as the hydrophobicity of amides increases in the order of NMF < NMA < DMF < NMP. Thus, the evolution of HFIP clusters around amides due to the hydrophobic interaction gives rise to phase separation of the mixtures. In contrast, the disruption of HFIP clusters causes the recovery of the homogeneity of the ternary systems. The present results showed that HFIP clusters are evolved with increasing amide content to the lower phase separation concentration in the same mechanism among the four amide systems. However, the disruption of HFIP clusters in the NMP and DMF systems with further increasing amide content to the upper phase separation concentration occurs in a different way from those in the NMF and NMA systems.     

Miniaturized salting-out liquid-liquid extraction of sulfonamides from different matrices

Salting-out liquid-liquid extraction (LLE) uses water-miscible organic solvents as the extractants. The principle of it is based on the phase separation of water-miscible organic solvents from the aqueous solutions in the presence of high concentration of salts. As an effort to miniaturization, in the present study, a 1-mL syringe was employed as the phase separation device for salting-out LLE. Once the phase separation occurred, the upper layer could be narrowed into the needle tip by pushing the plunger; thus, the collection of the upper layer solvent was convenient. By miniaturization, the consumption of organic solvent was decreased as low as possible. Four sulfonamides were used as model analytes. The optimal salting-out parameters were as follows. 150 μL of acetonitrile was added to the 500 μL of sample solution containing 300 mg mL(-1) sodium chloride at a pH of 6.5. This procedure afforded a convenient, fast and cost-saving operation with good cleanup ability for the model analytes. It showed promising applications for different matrices. Herein, food (honey), environmental water (river water) and biological fluid (human urine) were investigated. Satisfactory results were obtained. An additional bonus of this sample preparation method is that, owing to its water-miscible nature, the extraction solvent is compatible with various analytical systems, like gas chromatography, high-performance liquid chromatography and capillary electrophoresis.     

Nonlinear mixture‐wise expansion approach to underdetermined blind separation of nonnegative dependent sources

Underdetermined blind separation of nonnegative dependent sources consists in decomposing a set of observed mixed signals into greater number of original nonnegative and dependent component (source) signals. That is an important problem for which very few algorithms exist. It is also practically relevant for contemporary metabolic profiling of biological samples, such as biomarker identification studies, where sources (a.k.a. pure components or analytes) are aimed to be extracted from mass spectra of complex multicomponent mixtures. This paper presents a method for underdetermined blind separation of nonnegative dependent sources. The method performs nonlinear mixture‐wise mapping of observed data in high‐dimensional reproducible kernel Hilbert space (RKHS) of functions and sparseness‐constrained nonnegative matrix factorization (NMF) therein. Thus, the original problem is converted into new one with increased number of mixtures, increased number of dependent sources, and higher‐order (error) terms generated by nonlinear mapping. Provided that amplitudes of original components are sparsely distributed, which is the case for mass spectra of analytes, sparseness‐constrained NMF in RKHS yields, with significant probability, improved accuracy relative to the case when the same NMF algorithm is performed on the original problem. The method is exemplified on numerical and experimental examples related respectively to extraction of 10 dependent components from five mixtures and to extraction of 10 dependent analytes from mass spectra of two to five mixtures. Thereby, analytes mimic complexity of components expected to be found in biological samples. Copyright © 2013 John Wiley & Sons, Ltd.     

手性多孔材料在色谱分离分析中的应用

手性多孔有机骨架材料(Chiral porous organic frameworks,CPOFs)具有孔性质优异、比表面积高、稳定性好以及易功能化等诸多优点,已经在手性催化、识别和分离等领域中得到应用。手性多孔有机骨架材料主要有手性金属-有机骨架材料(Chiral metal-organic frameworks,CMOFs)和手性共价有机骨架材料(Chiral covalent organic frameworks,CCOFs)及其他材料,这类材料具有特殊的手性识别、吸附作用,在色谱分离分析领域中已成为研究热点之一。该文综述了手性多孔材料的合成及其在色谱分离和选择性吸附中的应用,展望了未来CPOFs材料可能的应用与发展方向。     

Thermally reversible light scattering films based on the melting/crystallization of organic crystals dispersed in an epoxy matrix

Films that can be reversibly switched from opaque to transparent states by varying temperature (TRLS films), have potential applications in thermal sensors, optical devices, recording media, etc. A dispersion of organic crystals in a thermoset may be used for these purposes provided that at temperatures higher than the melting point there is a matching of refractive indices of both phases. A model system consisting on a dispersion of diphenyl (DP) crystals in an epoxy matrix based on diglycidyl ether of bisphenol A and m-xylylenediamine, was analyzed as a possible TRLS film encapsulated between transparent covers to avoid sublimation of DP. To obtain a uniform dispersion of DP-rich domains in the epoxy matrix by polymerization-induced phase separation, it was necessary to add 5 wt% of polystyrene (PS) to the initial formulation. Phase separation induced by polymerization at 80 °C led to a dispersion of PS/DP domains in the epoxy matrix due to the low compatibility of PS with the epoxy and its high compatibility with DP. Crystallization and melting processes were confined to the interior of dispersed domains leading to an excellent reproducibility of the optical properties of TRLS films in the course of successive heating-cooling cycles.     

Pressure-assisted capillary electrophoresis for cation separations using a sequential injection analysis manifold and contactless conductivity detection

Pressure assisted capillary electrophoresis in capillaries with internal diameters of 10 μm was found possible without significant penalty in terms of separation efficiency and sensitivity when using contactless conductivity detection. A sequential injection analysis manifold consisting of a syringe pump and valves was used to impose a hydrodynamic flow in the separation of some inorganic as well as organic cations. It is demonstrated that the approach may be used to optimize analysis time by superimposing a hydrodynamic flow parallel to the electrokinetic motion. It is also possible to improve the separation by using the forced flow to maintain the analytes in the capillary, and thus the separation field, for longer times. The use of the syringe pump allows flexible and precise control of the pressure, so that it is possible to impose pressure steps during the separation. The use of this was demonstrated for the speeding up of late peaks, or forcing repeated passage of the sample plug through the capillary in order to increase separation.     

Overlapping spectra resolution using non-negative matrix factorization

Non-negative matrix factorization (NMF), with the constraints of non-negativity, has been recently proposed for multi-variate data analysis. Because it allows only additive, not subtractive, combinations of the original data, NMF is capable of producing region or parts-based representation of objects. It has been used for image analysis and text processing. Unlike PCA, the resolutions of NMF are non-negative and can be easily interpreted and understood directly. Due to multiple solutions, the original algorithm of NMF [D.D. Lee, H.S. Seung, Nature 401 (1999) 788] is not suitable for resolving chemical mixed signals. In reality, NMF has never been applied to resolving chemical mixed signals. It must be modified according to the characteristics of the chemical signals, such as smoothness of spectra, unimodality of chromatograms, sparseness of mass spectra, etc. We have used the modified NMF algorithm to narrow the feasible solution region for resolving chemical signals, and found that it could produce reasonable and acceptable results for certain experimental errors, especially for overlapping chromatograms and sparse mass spectra. Simulated two-dimensional (2-D) data and real GUJINGGONG alcohol liquor GC-MS data have been resolved soundly by NMF technique. Butyl caproate and its isomeric compound (butyric acid, hexyl ester) have been identified from the overlapping spectra. The result of NMF is preferable to that of Heuristic evolving latent projections (HELP). It shows that NMF is a promising chemometric resolution method for complex samples.     

Hydrogen production from bio-oil by chemical looping reforming

Hydrogen is a green energy carrier. Chemical looping reforming of biomass and its derivatives is a promising way for hydrogen production. However, the removal of carbon dioxide is costly and inefficient with the traditional chemical absorption methods. The objective of this article is to find a new material with low energy consumption and high capacity for carbon dioxide storage. A metal organic framework (MOF) material (e.g., CuBTC) was prepared using the hydrothermal synthesis method. The synthesized material was characterized by X-ray diffraction, ?196 °C N₂ adsorption/desorption isotherms, and thermogravimetry analysis to obtain its physical properties. Then BET, t-plot, and density functional theory (DFT) methods were used to acquire its specific surface area and pore textural properties. Its carbon dioxide adsorption capacity was evaluated using a micromeritics ASAP 2000 instrument. The results show that the decomposition temperature of the synthesized CuBTC material is 300 °C. Besides, high CO₂ adsorption capacity (4 mmol g^?1) and low N₂ adsorption capacity were obtained at 0 °C and atmospheric pressure. These results indicate that the synthesized MOF material has a high efficiency for CO₂ separation. From this study, it is expected that this MOF material could be used in adsorption and separation of carbon dioxide in chemical looping reforming process for hydrogen production in the near future.     

Exciton Transport in Molecular Semiconductor Crystals for Spin-Optoelectronics Paradigm

Organic semiconductors with long-range exciton diffusion length are highly desirable for optoelectronics but currently remain rare. Here, the estimated diffusion length of singlet excitons (L_D) in 2,6-diphenyl anthracene (DPA) crystals grown by solvent evaporation was shown to be up to approximately 124 nm. These crystals showed a previously unseen parallelogram morphology with layer-by-layer edge-on molecular stacking, isotropic optical waveguiding, radiation rate and non-radiation rate constants of 0.15 and 0.26 ns⁻¹ respectively, as well as good field-effect transistor hole mobility and theoretically computed strong electronic couplings as high as 109 meV. Photoresponse experiments revealed that the photoconductivity of DPA crystals is surprisingly not related to the radiative pathway but associated with rapid exciton diffusion to the crystal surface for charge separation and carrier bimolecular recombination. Taken together, DPA was shown to be a promising semiconducting material for a new organic optoelectronics paradigm.     

Nonaqueous capillary electrophoresis-mass spectrometry for separation of venlafaxine and its phase I metabolites

Aqueous and nonaqueous capillary electrophoresis (NACE) were investigated for separation of venlafaxine, a new second-generation antidepressant, and its three phase I metabolites. Working at basic pH, around the venlafaxine pKa value, was effective in resolving the investigated drugs, but created considerable peak tailing. To overcome electrostatic interactions between analytes and silanol groups, investigations were also carried out at acidic pH. However, despite the addition of up to 50% v/v of organic solvents (e.g., methanol or acetonitrile), complete separation of the studied compounds was not possible. NACE was found to be an appropriate alternative to resolve venlafaxine and its metabolites simultaneously. Using a conventional capillary (fused-silica, 64.5 cm length, 50 microm inner diameter), and a methanol-acetonitrile mixture (20/80 v/v) containing 25 mM ammonium formate and 1 M formic acid, complete resolution of these closely related compounds was performed in less than 3.5 min. Selectivity, efficiency and separation time were greatly affected by the organic solvent composition. As the electric current generated in nonaqueous medium was very low, the electric field was further increased by reducing the capillary length. This allowed a baseline resolution of venlafaxine and its three metabolities in 0.7 min. Selectivity was compared in aqueous and nonaqueous media in relation to the acid-base properties of the analytes as well as to the solvation degree. Finally, the method successfully coupled on-line to mass spectrometry with electrospray ionization interface allowed significant sensitivity enhancement.     

DNA sequencing of close to 1000 bases in 40 minutes by capillary electrophoresis using dimethyl sulfoxide and urea as denaturants in replaceable linear polyacrylamide solutions

The goal of this work was to reduce the capillary electrophoresis (CE) separation time of DNA sequencing fragments with linear polyacrylamide solutions while maintaining the previously achieved long read lengths of 1000 bases. Separation speed can be increased while maintaining long read lengths by reducing the separation matrix viscosity and/or raising the column temperature. As urea is a major contributor to the separation buffer viscosity, reducing its concentration is desirable both for increase in the separation speed and easier solution replacement from the capillary. However, at urea concentrations below 6 M, the denaturing capacity of the separation buffer is not sufficient for accurate base-calling. To restore the denaturing properties of the buffer, a small amount of an organic solvent was added to the formulation. We found that a mixture of 2 M urea with 5% v/w of dimethyl sulfoxide (DMSO) resulted in 975 bases being sequenced at 70 degrees C in 40 min with 98.5% accuracy. To achieve this result, the software was modified to perform base-calling at a peak resolution as low as 0.24. It is also demonstrated that the products of thermal decomposition of urea had a deleterious effect on the separation performance at temperatures above 70 degrees C. With total replacement of urea with DMSO, at a concentration of 5% v/w in the same linear polyacrylamide (LPA)-containing buffer, it was possible to increase the column temperature up to 90 degrees C. At this temperature, up to 951 bases with 98.5% accuracy could be read in only 32 min of separation. However, with DMSO alone, some groups of C-terminated peaks remained compressed, and column temperature at this level cannot at present be utilized with existing commercial instrumentation.     

New Polymers for Optimizing Organic Photovoltaic Cell Performances

The performance of an organic solar cell critically depends on the materials used in the active layer. Desirable characteristics of active layer materials include an intense optical absorption covering broad range of the solar spectrum to maximize photon capture, the ability to effectively separate charges upon photo‐excitation, high charge mobility to allow efficient charge transport to the electrodes, and suitable HOMO and LUMO levels to ensure a high device voltage. In order to optimize these properties simultaneously, we have designed and synthesized conjugated polymers containing alternating electron‐donating and electron‐accepting units. Based on one of the low band gap polymers we designed and synthesized previously, poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)], we carried out both side chain and main chain modifications in order to improve performance even further. By incorporating fluorene repeating units into the main chain, it is possible to adjust the absorption characteristics of the polymers while maintaining a desirable HOMO level and good charge carrier mobility. The solubility profile of the polymer can be adjusted by modifying the side chains, and soluble polymer with mobility as high as 7×10^?2 cm²/Vs is realized when a combination of 2‐ethylhexy and hexyl groups are used as side chains. These polymers should be promising candidates for high performance solar cells according to a recently published model (3).     

Uniform polyolefin and polymethacrylate

Preparations and properties of synthetic uniform polyolefins and polymethacrylates are described with emphasizing the necessity of their utilization for understanding the fundamental problems in polymer chemistry. Uniform polymer is a polymer composed of molecules uniform with respect to molecular weight and constitution. While classical organic chemistry provides means of constructing uniform polymers such as poly(methylene)s in stepwise manners, recent advances in separation technology such as supercritical fluid chromatography (SFC) have made it possible to isolate synthetic uniform polymers from its homologous mixture. Combinations of stereospecific polymerizations and the SFC technique have enabled us to prepare uniform polystyrenes and poly(methyl methacrylate)s with high stereoregularities, which are very useful for systematic studies on the nature of polymers. The thermal properties of these uniform polymers are discussed in some detail.     

Separation of mixed gases through porous polymeric membranes

The separation of a gas from a two component gas system was studied both theoretically and experimentally. Helium and argon as an inorganic gas pair, ethylene and butane as an organic gas pair, and air were used. The theory based on the free molecular flow could not be applied to all the combinations of the gases experimentally studied. Experiments showed that the permeability coefficient of each component in the mixture was very close to that of each single component, when the pressure in the low pressure side became zero, but those of the mixture approached one another rapidly as the pressure increased. In the case of the separation of one inorganic gas from another, there exists most suitable pressures both in the high and low pressure sides for the most efficient separation, as considered from the selectivity and permeability. In the cases of the mixed organic gases and the organic-inorganic gas combination, a rather high separation efficiency is expected for a very high pressure on the high pressure side.     

基于离子液体的双水相体系的分离机理及应用

离子液体由于具有非挥发性、低毒、不易燃、热稳定性及化学稳定性高等优势,被认为是可替代传统有机溶剂的"绿色溶剂",在双水相体系构建方面得到了广泛应用。基于离子液体的双水相体系在生物大分子及有机化合物萃取分离方面具有独特优势,如萃取快速,操作简单,不需使用有害有机溶剂及复杂设备,易于规模化且生物兼容性好。该文综述了基于离子液体的双水相体系的两相分离机理及其在有机小分子及生物样品萃取纯化中的应用。并在此基础上讨论了离子液体双水相体系的优势、缺点以及未来发展趋势。     

A novel trilinear decomposition algorithm： Three-dimension non-negative matrix factorization

Non-negative matrix factorization(NMF)is a technique for dimensionality reduction by placing non-negativity constraints onthe matrix.Based on the PARAFAC model,NMF was extended for three-dimension data decomposition.The three-dimension non-negative matrix factorization(NMF3)algorithm,which was concise and easy to implement,was given in this paper.The NMF3algorithm implementation was based on elements but not on vectors.It could decompose a data array directly without unfolding,which was not similar to that the traditional algorithms do.It has been applied to the simulated data array decomposition andobtained reasonable results.It showed that NMF3 could be introduced for curve resolution in chemometrics.     

The influence of organic sample solvents on the separation efficiency of basic compounds under strong cation exchange mode

This study investigated the influence of organic sample solvents on separation efficiency of basic compounds under strong cation exchange (SCX) mode. The mixtures of acidic aqueous solution and organic solvent such as acetonitrile, ethanol, methanol and dimethyl sulfoxide (DMSO) were tested as sample solvents. For later-eluting analytes, the increase of sample solvent elution strength was responsible for the decrease of separation efficiency. Thus, sample solvents with weak elution strength could provide high separation efficiencies. For earlier-eluting analytes, the retention of organic sample solvents was the main factor affecting separation efficiency. Weakly retained solvents could provide high separation efficiency. In addition, an optimized approach was proposed to reduce the effect of organic sample solvent, in which low ionic solvent was employed as initial mobile phase in the gradient. At last, the analysis of impurities in hydrophobic drug berberine was performed. The results showed that using acidic aqueous methanol as sample solvents could provide high separation efficiency and good resolution (R > 1.5).     

Liquid-crystalline polypropyleneimine dendrimer as a stationary phase for gas chromatography

The adsorption properties of a stationary phase for gas chromatography based on a Chromaton N-AW diatomite support modified with a 2K2S16 mesomorphic polypropyleneimine dendrimer are studied. Using the Rohrschneider constants, the studied stationary phase is classified as low polar. It is shown that the new stationary phase is suitable for the separation of both isomers and mixtures of organic substances bearing various functional groups up to a temperature of 150°C.