Membrane rectification columns for gas separation and determination of the operating lines using the mccabe—thiele diagram

A new continuously operating separating unit — a membrane rectification column — has been developed for the separation of gases by membranes. The membrane rectification column can be characterized as a “step-by-step separating process”. In this article the equations for the operating lines have been constructed to show the separating process with the new enrichment technique in the McCabe—Thiele diagram.     

Correlation of Migration Distance of Peptides in High-Performance Thin-Layer Chromatography and Pressurized Planar Electrochromatography Systems

In a series of our previous papers we have investigated the influence of various variables on retention/migration of peptides in various high-performance thin-layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC) systems. Here we present a correlation of the selectivity of peptide separation in similar, as well as in various HPTLC and PPEC systems investigated before. Our results show that the selectivity in similar HPTLC and PPEC systems is quite different. This results from the share of electrophoresis in separation of solutes by PPEC. The results suggest that combination of HPTLC and PPEC, with properly selected separation conditions (the same, or even better—different for each technique), may be used for efficient two-dimensional separation of peptides. The best separation can be obtained if PPEC is carried out in two opposite directions (toward the cathode and the anode) simultaneously.     

The effect of solute—membrane affinity on cyclic hydrocarbon—water transport in pressure-driven membrane separation processes

Experimental results for the pressure-driven membrane separation of cyclic hydrocarbons (1,3-cyclohexadiene, cyclohexene, and cyclohexane) from dilute binary aqueous solution using asymmetric cellulose acetate membranes are reported here. In these experiments, total solution fluxes are significantly lower than pure water fluxes at the same applied pressure; this flux reduction is attributed to strong solute—membrane affinity rather than to the osmotic pressure of either the bulk retentate or the boundary layer. An empirical parameter, Z, is used to describe flux reduction. A theoretically based friction parameter, B, is derived assuming the membrane can be represented as an ideal, finely porous membrane; this parameter indicates the influence of solute—membrane affinity on flow through the pores of the membrane. Both the empirical parameter Z and the theoretically based parameter B relate flux reduction to concentrations in the system. Both Z and B increase as solute—membrane affinity increases and decrease as membrane pore size increases. It is concluded that both the empirical flux reduction parameter, Z, and the theoretically based friction parameter, B, indicate the same system properties: solute—membrane affinity and membrane pore size.     

Coordination-Ionspray-MS (CIS-MS), a Universal Detection and Characterization Method for Direct Coupling with Separation Techniques

By on-line addition of a central atom (for example, Ag^I, B^III, Pd^II, Li^I) positively or negatively charged complexes of analytes can be formed for CIS-MS. This technique is applicable to both polar and nonpolar compounds—for example, for alcohols, ethers, and a large number of olefins, polyolefins, and arenes as well as steroids, vitamins of the D and E families, carotinoids, polystyrols, terpenes, and unsaturated fatty acids—and can be readily coupled with separation techniques.     

O-(α-Phenylethyl)hydroxylamine as a ‘chiral ammonia equivalent’: synthesis and resolution of 5-oxopyrrolidine- and 6-oxopiperidine-3-carboxylic acids

An approach to the synthesis and resolution of five- and six-membered lactams (i.e., 5-oxopyrrolidine- and 6-oxopiperidine-3-carboxylic acids) is described. The method relies on the one-pot Michael reaction—cyclization of itaconic acid or diethyl homoitaconate and enantiopure O-(α-phenylethyl)hydroxylamine as a ‘chiral ammonia equivalent’. It is shown that this chiral auxiliary can be used for the separation of diastereomeric lactam products and then easily removed by catalytic hydrogenolysis.     

Verification of epitaxial growth and determination of chain positions in Langmuir—Blodgett films of lead stearate on mica

We have determined from X-ray diffraction that lead stearate, which like many hydrocarbon compounds does not form good crystals in bulk, can be grown epitaxially on mica using the Langmuir—Blodgett technique. The strong alternation in intensities of the (11l) peaks cannot be explained by considering the lead ions only, and imply that the hydrocarbon chains do not close-pack into a triangular array but reproduce the in-plane structure of the lead ions.     

Sorption and pervaporation of dilute aqueous solutions of organic compounds through polymer membranes

Pervaporation of dilute aqueous binary mixtures of four organic compounds (benzene, chloroform, acetone and ethanol) through nitrile—butadiene and styrene—butadiene copolymers was investigated. A pervaporation device has been built, which allows measurement of the pervaporation flux and selectivity of a membrane as a function of the upstream composition of the feed and the downstream total pressure of the pervaporate. In order to relate pervaporation results to equilibrium properties of the membranes, the sorption of water and dilute aqueous solutions was mainly investigated. The pervaporation of dilute aqueous solutions of benzene and chloroform has been extensively studied, including the separation of traces of chloroform, and is modelled through a “sixcoefficients exponential model” [1]. This model is derived from a solution—diffusion analysis of the selective transfer, assuming an exponential dependence of both diffusivities on concentrations of both permeants. Semi-quantitative information about the potential interactions existing in the system solute i—solvent j—membrane and about the concentration profiles at steady-state may be derived from these coefficients.     

Liquid chromatographic enantiomeric resolution of amino acids with β-cyclodextrin bonded phases and derivatization with o-phthalaldehyde

The reaction of amino acids with o-phthalaldehyde (OPA) and 2-mercaptoethanol is evaluated as a precolumn derivatization technique in order to achieve the chiral separation and final fluorimetric detection of l,d-glutamic acid in β-cylodextrin bonded phases. The pertinent chromatographic parameters were determined and the effect of organic modifiers, pH, ionic strength and temperature on retention and resolution were evaluated. The chromatographic method finally developed allowed the optical resolution of OPA-derivatized l- and d-glutamic acid using methanol—1% triethylammonium acetate (pH 7.4) (30 + 70, v/v) as eluent.     

Optimum collision energies for proteomics: The impact of ion mobility separation

Ion mobility spectrometry (IMS) is a widespread separation technique used in various research fields. It can be coupled to liquid chromatography–mass spectrometry (LC–MS/MS) methods providing an additional separation dimension. During IMS, ions are subjected to multiple collisions with buffer gas, which may cause significant ion heating. The present project addresses this phenomenon from the bottom-up proteomics point of view. We performed LC–MS/MS measurements on a cyclic ion mobility mass spectrometer with varied collision energy (CE) settings both with and without IMS. We investigated the CE dependence of identification score, using Byonic search engine, for more than 1000 tryptic peptides from HeLa digest standard. We determined the optimal CE values—giving the highest identification score—for both setups (i.e., with and without IMS). Results show that lower CE is advantageous when IMS separation is applied, by 6.3 V on average. This value belongs to the one-cycle separation configuration, and multiple cycles may supposedly have even larger impact. The effect of IMS is also reflected in the trends of optimal CE values versus m/z functions. The parameters suggested by the manufacturer were found to be almost optimal for the setup without IMS; on the other hand, they are obviously too high with IMS. Practical consideration on setting up a mass spectrometric platform hyphenated to IMS is also presented. Furthermore, the two CID (collision induced dissociation) fragmentation cells of the instrument—located before and after the IMS cell—were also compared, and we found that CE adjustment is needed when the trap cell is used for activation instead of the transfer cell. Data have been deposited in the MassIVE repository (MSV000090944).     

Hydrogen-bonding-driven self-assembly nonporous adaptive crystals for the separation of benzene from BTX and cyclohexane

Benzene is a volatile organic compound that can seriously harm human health, while it can serve as a precursor to produce chemicals of more complex structures in chemical industry. Capturing benzene using adsorbents is of great importance for human health, when the separation of hydrocarbons including benzene from crude oil was referred to as one of the “seven chemical separations to change the world”. In this work, we reported the efficient and selective separation of benzene from BTX and cyclohexane by hydrogen bonding self-assembly nonporous adaptive crystals AdaOH for the first time under mild and user-friendly conditions. Separation of benzene and cyclohexane (v/v = 1:1) can be achieved by AdaOH with a purity of benzene up to 96.8%. Separation of BTX (v/v; benzene:toluene:o-xylene:m-xylene:p-xylene= 1:1:1:1:1) can be achieved by AdaOH with a purity of benzene increased from 20% to 82.9%. Our results suggest that separation of benzene using the activated AdaOH as a non-porous adaptive crystal for selectively and efficiently capturing benzene can solve the challenge in separation of benzene from other chemicals such as cyclohexane in chemical industry, and can be helpful for removal of benzene that is released from the vehicles to air. The advantages of commercially availability, easy preparation, high separation efficiency and selectivity for benzene might endow this material with enormous potential for practical uses in areas like petrochemical industry.     

Liquid-liquid phase separation of binary Lennard-Jones fluid in slit nanopores

The capillary phase separation of a binary mixture of two truncated and shifted Lennard-Jones (LJ) Ar liquids in slit-shaped oxygen nanopores is examined. The LJ parameters—ε(Ar(A)–Ar(A))=ε(Ar(B)–Ar(B))=0.8ε(Ar(A)–Ar(B)) and 0.5ε(Ar(A)–O)?=?ε(Ar(B)–O)—were used to distinguish the two Ar liquids. The cut off distance for Ar was 3.5σ. We employed a molecular dynamics (MD) technique in which a pore space was connected with a bulk solution to easily determine the equilibrium bulk concentration. Liquid phase isotherms were obtained for pores with widths ranging from 5.5σ to 9.5σ, and the relation between the pore width and the phase separation concentration was determined. Each simulation was run until the bulk concentration attained equilibrium (1–2 μs). The MD results show that the Patrick model overestimates the bulk concentration for a given pore size. We proposed a modified Patrick model in which the pore wall potential is considered. In our model, the Gibbs-Tolman-Koenig-Buff effect is not considered for the interfacial tension since two surfaces of tension exist on both sides of the equimolar dividing surface of the two-Ar liquid phase. The two surfaces of tension neutralized Gibbs-Tolman-Koenig-Buff effect each other. The present simple model successfully describes the relation to prove its reliability.     

Determination of molecular formulas of natural organic matter molecules by (ultra-) high-resolution mass spectrometry: Status and needs

Electrospray ionization (ESI) combined with ultra-high-resolution mass spectrometry on a Fourier transform ion cyclotron resonance mass spectrometer has been shown to be a very powerful tool for the analysis of fulvic and humic acids and of natural organic matter (NOM) at the molecular level. With this technique thousands of ions can be separated from each other and their m/z ratio determined with sufficient accuracy to allow molecular formula calculation. Organic biogeochemistry, water chemistry, and atmospheric chemistry greatly benefit from this technique. Methodical aspects concerning the application of Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) to NOM isolated from surface water, groundwater, marine waters, and soils as well as from secondary organic aerosol in the atmospheric are reviewed. Enrichment of NOM and its chromatographic separation as well as possible influences of the ionization process on the appearance of the mass spectra are discussed. These steps of the analytical process require more systematic investigations. A basic drawback, however, is the lack of well defined single reference compounds of NOM or fulvic acids. Approaches of molecular formula calculation from the mass spectrometric data are reviewed and available graphical presentation methods are summarized. Finally, unsolved issues that limit the quality of data generated by FTICR-MS analysis of NOM are elaborated. It is concluded that further development in NOM enrichment and chromatographic separation is required and that tools for data analysis, data comparison and data visualization ought to be improved to make full use of FTICR-MS in NOM analysis.     

Development of Electrophoretic Methods for Simultaneous Determination of Enantiomeric Ratio and Composition of Diastereomeric Salt Mixtures

Obtaining enantiomeric pure compounds is—among other techniques—possible in a resolvation experiment via diastereomeric salt formation, excellently exemplified by a modified Pope–Peachy method performed in supercritical carbon dioxide as solvent. The salt precipitation is followed by supercritical fluid extraction (SFE) to separate the diastereomeric salts and the unreacted enantiomers. To evaluate the extraction efficiency, conversion and enantioselectivity achieved, it is essential to determine the enantiomer excess and the residual resolving agent content in extracts and raffinates. Carefully chosen experimental parameters enable the simultaneous determination of certain anions and cations in capillary electrophoresis in a single run, which has not been reported for diastereomeric mixtures so far. In this paper, a partially validated chiral selective cyclodextrin enabled capillary electrophoresis method is presented for the characterization of cis-permethrinic acid samples resolved with (R)-1-phenylethylamine prepared by the SFE-based resolvation technique. To evaluate the efficiency of the resolvation, a cyclodextrin enabled chiral separation method was developed applying permethylated-β-cyclodextrin as chiral selector. The theoretical possibility of the widespread application of the developed method (with minor adjustments) is justified for other selectands and selectors. The developed methods can be thereby applied for the fast and reliable control of resolvation experiments.     

Anodic stripping voltammetry of tellurium(IV) in aqueous solution and mixed solvents

The anodic stripping determination of Te(IV) using a rotating glassy carbon disc electrode is described. 0.1 ppm tellurium can be determined in 1 M HCl. Interfering effects of the metals forming intermetallic compounds with tellurium on the electrode are eliminated by solvent extraction. Te(IV) is determined either after its extraction — as an ion associate or as the chelate with diphenylthiocarbazone — in the organic phase which is adjusted for the stripping determination by the addition of methanolic solution of LiCl or after the separation of all interfering elements by an extraction procedure involving the extraction of Te(IV) into methylisobutylketone and back extraction of Te(IV) with water followed by the separation of the remaining interfering elements into diisopropylether. The proposed method enables the determination of 10 μg Te in the presence of 25 mg Pb and Sb and 0.5 mg Ag, Cu, Bi, As, Sn, Cd, Zn with reproducible results and error ±5%.     

Cation-exchange separations in organic solvent-dithizone media

Numerous elements can be adsorbed on a column of the strongly acidic cation-exchange resin Dowex 50 from a mixture consisting of tetrahydrofuran and 1 M nitric acid (19:1). These elements include Ag, Cu, Bi, Pb, rare earths, alkaline earth metals, alkali metals, U, Th, Fe, Co, Zn and Cd; Hg and Sb are not retained and so can be separated from the adsorbed elements. Fractionation of the adsorbed elements can be effected by using as eluent 0.01 M dithizone in tetrahydrofuran-1 M nitric acid(19:1);; the dithizonates of silver, copper and bismuth are selectively eluted while the other adsorbed metal ions are still retained. The technique is suitable for the separation of tracer and macro amounts of elements.     

Separation of benzene—n-heptane mixtures by pervaporation with elastomeric membranes. II. Contribution of sorption to the separation mechanism

The separation mechanism of pervaporation can be considered as consisting of two steps: sorption at the upper solution—membrane interface and diffusion through the membrane. In the system benzene—n-heptane—poly(butadiene—acrylonitrile) (NBR)membrane, sorption is studied according to the same parameters as pervaporation [1]; it emphasizes the importance of nitrile groups in the separation and reveals, for lower swellings, an equivalent contribution of the two steps in the separation mechanism. This permits sorption selectivity to be taken as a first approximation of pervaporation selectivity.     

Die optische Aktivität von 2,2′-Spiro-biindan-1,1′-dion

From the circular dichroism of optically active 2.2′-spirobiindane-1.1′-dione and its precursor in several solvents as well as from the liquid crystal induced circular dichroism in connection withPPP-type calculations can be concluded that the optical activity of the n—π* is best understood in terms ofWeigang's generalized vibronic scheme; the n—π* can be rationalized on the basis of the coupled oscillator theory.     

Immunomagnetic nanoparticle based quantitative PCR for rapid detection of Salmonella

We have developed a rapid and sensitive method for immunomagnetic separation (IMS) of Salmonella along with their real time detection via PCR. Silica-coated magnetic nanoparticles were functionalized with carboxy groups to which anti-Salmonella antibody raised against heat-inactivated whole cells of Salmonella were covalently attached. The immuno-captured target cells were detected in beverages like milk and lemon juice by multiplex PCR and real time PCR with a detection limit of 10⁴ cfu.mL^?1 and 10³ cfu.mL^?1, respectively. We demonstrate that IMS can be used for selective concentration of target bacteria from beverages for subsequent use in PCR detection. PCR also enables differentiation of Salmonella typhi and Salmonella paratyphi A using a set of four specific primers. In addition, IMS—PCR can be used as a screening tool in the food and beverage industry for the detection of Salmonella within 3–4 h which compares favorably to the time of several days that is needed in case of conventional detection based on culture and biochemical methods.

Reprint of: Application of micro-thin-layer chromatography as a simple fractionation tool for fast screening of raw extracts derived from complex biological,pharmaceutical and environmental samples

The main goal of present paper is to demonstrate the separation and detection capability of micro-TLC technique involving simple one step liquid extraction protocols of complex materials without multi-steps sample pre-purification. In the present studies target components (cyanobacteria pigments, lipids and fullerenes) were isolated from heavy loading complex matrices including spirulina dried cells, birds’ feathers and fatty oils as well as soot samples derived from biomass fuel and fossils-fired home heating systems. In each case isocratic separation protocol involving less that 1 mL of one component or binary mixture mobile phases can be completed within time of 5–8 min. Sensitive detection of components of interest was performed via fluorescence or staining techniques using iodine or phosphomolybdic acid. Described methodology can be applied for fast fractionation or screening of whole range of target substances as well as chemo-taxonomic studies and fingerprinting of complex mixtures, which are present in raw biological or environmental samples.     

Liquid chromatographic separation of the thyroid hormones

The liquid Chromatographic separation of 3,3',5-triiodothyronine, 3,3',5'-triiodothyronine, and thyroxine with a nonpolar stationary phase was studied as a function of pH, temperature, organic content of the mobile phase, and ionic strength using aqueous phosphate—acetonitrile, aqueous phosphate—methanol, and aqueous phosphate— n-propanol mobile phase systems. It was demonstrated that the quality of the thyroid hormone separations, as determined by normalized peak capacity values, was unchanged with temperature, remained relatively constant with increasing ionic strength, and was affected to the greatest extent by changes in pH and organic modifier content of the mobile phase. Chromatographic behavior of the compounds studied as a function of these variables was found to be consistent with existing Chromatographic theory and/or empirical observations. Recommended conditions are aqueous phosphate—methanol mobile phase, pH 2–5 (aqueous portion), and high temperature (60–70°C).