The separation power and thermodynamic work of separation for a three-flow unit during the equilibrium separation of a binary gas mixture

Equations for calculating the separation power and thermodynamic work of a three-flow separation element and cascade for the separation of a binary gas mixture are discussed.     

Ion separation on a thread

Summary Preliminary trials indicate that the sensitivity of separation by solvent extraction may be improved by concentrating the extracts upon a thread. Chromatographic separation may be added to simplify the identification of the metals.

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Zusammenfassung Vorläufige Ergebnisse zeigen, daß die Möglichkeit besteht, die Empfindlichkeit der Kationentrennung durch stufenweise Extraktion zu steigern, indem man die Extrakte auf einem Nähfaden konzentriert. Chromatographische Trennung auf dem Faden kann dazu benutzt werden, den Nachweis der einzelnen Metalle zu vereinfachen.

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Résumé Des essais préliminaires indiquent que la sensibilité de la séparation par extraction avec un solvant peut être améliorée en concentrant les extraits sur un fil. La séparation chromatographique peut être ajoutée pour simplifier l'identification des métaux.

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On the occasion of the hundredth return ofFriedrich Emich's birthday.     

Direct conformational analysis of a 10 nm long oligothiophene wire

Conformational variations of a 10 nm long oligothiophene wire comprising 24 thiophene rings on Au(111), which are related to the various straight and bent shapes of the long wires, have been directly visualized by scanning tunneling microscopy (STM). The local bending angles within the wire are well characterized as s-cis/s-trans configurations of individual thiophene rings. We find that the partial stabilization of the metastable s-cis conformation results in the wire bending, which should be influenced by solvent and substituents.     

Towards a comprehensive 2-D-LC-MS separation

A comprehensive 2-D-LC-MS method has been developed by coupling columns of different selectivity. The primary column eluate is alternately trapped and sampled onto the secondary columns through a guard column interface. When one guard column traps the eluate, the other injects the previously trapped components onto a secondary column. This cycle is repeated throughout the chromatogram. The use of dual secondary columns provides the secondary columns with additional time to generate high-speed chromatograms. Each secondary column generates alternate chromatograms which when combined generate the entire chromatogram. The primary column separation is comparable to conventional HPLC, whereas the secondary column separation is fast. With both the columns operating in reverse phase mode, one would expect strong correlation in the two-dimensional retention and hence inefficiency in separation. However, differences in column operation modes, interaction mechanisms, and vendor silica result in a complementary separation. The system was evaluated by comparing it to one-dimensional counterparts and coupled column chromatography. Although some correlations were observed in 2-D-LC-MS, peaks do show two-dimensional distribution with superior UV and MS data as co-elution is minimized. Also, the ease of converting conventional systems to 2-D-LC-MS is discussed.     

DNA separation at a liquid-solid interface

We demonstrate that it is possible to separate a broad band of DNA on a solid substrate without topological obstacles. The mobility was found to scale with molecular size (N) as N(-0.25), while the resolution scaled as N(0.75) indicating that diffusivity on this substrate was minimal. By varying the buffer concentration we were able to show that the mobility for a given chain length scaled with the persistent length (p) as p(1/2). This could be shown to be related to the Gaussian conformation of the chains adsorbed on the surface. A two-dimensional corrugated surface of nonporous silica beads was produced using a self-assembling process at the air/water interface. Even though the surface corrugations were comparable to persistence length we show that they do not affect the mobility, indicating that surface friction rather than topological constraints are the predominant mechanism of separation on a surface.     

Thermodynamic work of separation of a multicomponent mixture

Equations for interpreting and calculating the work of separation of binary and multicomponent mixtures are discussed and generalized.     

Chromatographic separation of prebiotic oligosaccharides. Case study: separation of galacto-oligosaccharides on a cation exchanger

Chromatographic separation of prebiotic oligosaccharides, galacto-oligosaccharides from a typical post-reaction mixture containing unreacted substrate lactose and by-products glucose and galactose was investigated. A commercial cation-exchange resin Dowex 50WX4 was chosen as a prospective preparative-scale adsorbent and separation performance of its four ionic forms, H⁺, Na⁺, K⁺ and Ca²⁺, was tested. Since adsorption equilibrium isotherms were linear within the entire investigated range of concentrations, they were determined by pulse experiments for all saccharides present in a typical post reaction mixture including tri- and tetragalacto-oligosaccharides. From the four counter ions listed above, hydrogen offered the best selectivity and column performance. The selected H⁺-form of the cation exchanger was further investigated by means of frontal analysis where high ionic strength and elevated viscosity appear and can play a substantial role. Breakthrough curves were measured for monosaccharides, lactose, glucose–lactose mixture and a multicomponent commercial mixture of galacto-oligosaccharides, Vivinal^® GOS. The breakthrough curves were successfully described by the dispersive plug flow model with linear driving force approximation.     

Development of a relatively cheap and simple automated separation system for a routine separation procedure based on extraction chromatography

A robust analytical method has been developed in our laboratory for the separation of radionuclides by means of extraction chromatography using an automated separation system. The proposed method is both cheap and simple and provides the advantageous, rapid and accurate separation of the element of interest. The automated separation system enables a shorter separation time by maintaining a constant flow rate of solution and by avoiding clogging or bubbling in the chromatographic column. The present separation method was tested with two types of samples (water and urine) using UTEVA-, TRU- and Sr-specific resins for the separation of U, Th, Am, Pu and Sr. The total separation time for one radionuclide ranged from 60 to 100 min with the separation yield ranging from 68 to 98% depending on the elements separated. We used ICP-QMS, multi-low-level counter and alpha spectroscopy to measure the corresponding elements.     

A copper vapour laser operating at wavelengths of 303.6 nm and 306.3 nm

A commercial copper vapour laser has been modified to operate at wavelengths of 303.6 nm and 306.3 nm. The laser transition at 578 nm was suppressed, in order to enhance the competing U.V. transitions. The time averaged U.V. output power level is a few mW's at an electrical input power of up to 4.5 kW. The duration of the pulses is 68 ns.     

Number of adsorbers for a gas separation system

An algorithm for the total number of adsorbers and the number of active adsorbers (i.e., the ones in the adsorption mode at the moment in question) has been designed in terms of the ergodic hypothesis. This algorithm is intended for the design of gas separation systems.     

Phase separation of a binary two-dimensional core-softened fluid

Using molecular dynamics simulations, we study the phase separation in a binary two-dimensional core-softened fluid with different size ratios and concentrations. The correlation functions for both components are analyzed to show the dependence of the configurational structure of the binary fluid on size ratio and concentration. A phase separation diagram is obtained and the structural features of the phase separation are further investigated using the direct imaging method.     

Linear peak capacity of a comprehensive multi-dimensional separation

In order to resolve (quantifiably and identifiably separate) the same number of peaks in the analysis of the same mixture yielding statistically uniform peak distribution, a comprehensive 2-D separation needs a two times larger peak capacity than a 1-D separation does. Each additional dimension further reduces the utilization of the peak capacity of comprehensive multi-dimensional (MD) separation by a factor of two per dimension. As a result, the same peak capacity means different things for separations with different dimensionalities. This complicates the use of the peak capacity for comparison of the potential separation performance of the separations with different dimensionalities. To facilitate the comparison, a concept of a linear peak capacity has been proposed. The linear peak capacity of an MD separation is the peak capacity of a 1-D separation that, in the analysis of the same mixture, is statistically expected to resolve the same number of peaks as the MD separation is. There are other factors that differently affect the performance of the separations that have different dimensionalities. Peak capacity of a 2-D separation with a rectangular separation space is 27% larger than the product of the peak capacities of its first and second dimension. This advantage of a 2-D separation is essentially nullified by the fact that the peak capacity of the first dimension of an optimized 2-D separation cannot be higher than 80% of the peak capacity of its first dimension standing alone. All in all, the incremental peak capacity gained from addition of a second dimension will not exceed 50% of the peak capacity of the added second dimension. All results are valid for arbitrarily shaped (not necessarily Gaussian) peaks.     

Laser Induced Transient Structures in a 150 nm Gold Crystal

The evolution of transient structures induced in gold crystals by irradiation with 400 nm, 100 fs laser pulses has been measured by means of time resolved x‐ray diffraction. The data show that the photon/electron interaction generates a hot electron wave on a 150 nm Au crystal, which is responsible for a “blast force” that generates an intense shock wave that alters the lattice structure as it propagates, with sound velocity, through the bulk of the crystal. This mechanical force is developed within 1‐2 ps after the laser pulse interacts with the gold surface electrons. Other major effects that have contributed to the strain in the lattice have also been evaluated.     

Angular distribution of photo electrons from above-threshold-ionization (ATI) of xenon by 532 nm, 355 nm and 266 nm radiation

A time-of-flight electron energy spectrometer has been used to measure the angular distributions of photoelectrons emitted after the absorption of up to four excess photons above the ionization threshold of Xenon at 532 nm. For shorter wavelength less efficient ATI is observed. The shape of the angular distributions and the branching ratios for the two ionic fine structure states Xe⁺(² P _3/2) and Xe⁺(² P _1/2) may be plausibly attributed to the influence of excited states of the atom.     

Systematical Study on Photodissociation Dynamics of BrCN from 225 nm to 260 nm

The photodissociation dynamics of Br\begin{document}$ - $\end{document}C bond cleavage for BrCN in the wavelength region from 225 nm to 260 nm has been studied by our homebuilt time-slice velocity-map imaging setup. The images for both of the ground state Br(\begin{document}$ ^{2} {\rm{P}}_{3/2} $\end{document}) and spin-orbit excited Br\begin{document}$ ^* $\end{document}(\begin{document}$ ^{2} {\rm{P}}_{1/2} $\end{document}) channels are obtained at several photodissociation wavelengths. From the analysis of the translational energy release spectra, the detailed vibrational and rotational distributions of CN products have been measured for both of the Br and Br\begin{document}$ ^* $\end{document} channels. It is found that the internal excitation of the CN products for the Br\begin{document}$ ^* $\end{document} channel is colder than that for the Br channel. The most populated vibrational levels of the CN products are \begin{document}$ v $\end{document}=0 and 1 for the Br and Br\begin{document}$ ^* $\end{document} channels, respectively. For the Br channel, the photodissociation dynamics at longer wavelengths are found to be different from those at shorter wavelengths, as revealed by their dramatically different vibrational and rotational excitations of the CN products.     

Single-molecule electrical studies on a 7 nm long molecular wire

A self-assembled arylene-ethynylene molecular wire with a rigid 7 nm long backbone exhibits symmetrical current-voltage (I-V) characteristics and a single-molecule current of 0.35 +/- 0.05 nA at 0.3 V; these data are supported by theoretical calculations.     

Methane separation by a continuous membrane column

A continuous membrane column was employed to separate methane from gas mixtures of CO₂CH₄, CH₄N₂ and CO₂CH₄ N₂ at room temperature. Shell-side composition profiles along the column were taken experimentally and compared with the calculated results. The agreements were excellent, indicating that the model calculation is adequate for a ternary system. Combination of two columns was developed to separate the ternary mixture.