Separation of the Isotopes of Uranium by the Separation Nozzle Process

The separation nozzle process is based on the partial spatial separation of components of different mass in an expanding supersonic jet stream. The process is of especial interest for the separation of uranium isotopes. Details of a systematic experimental determination of the most favorable operating conditions for such a separation are given and the construction and testing of a closed circulation system, the basic unit of a ten membered pilot cascade separator for uranium isotope separation, is described. The optimum values of the specific cost factors obtained experimentally for the separation nozzle process are compared with the corresponding values estimated for the gaseous diffusion process.     

Development of overlapping repeated separation of steviol glycosides with counter current chromatography and a comparison with a conventional repeated separation method

Repeated separation is a valuable method in counter current chromatography, especially on a preparative scale. It can greatly reduce the separation time and the consumption of solvent. In this study, an overlapping repeated separation method was developed. Meanwhile, this method was used to separate steviol glycosides and compared with conventional repeated separation method. The results show that both methods are effective ways for countercurrent chromatography to prepare compounds but the overlapping repeated separation method requires fewer time and solvent than the conventional repeated separation method. So this novel repeated separation method has enormous potential for a preparative separation of target compounds and is very useful for the high‐throughput purification of natural products.     

The extent of separation in single permeation stages

Rony's extent of separation is used to compare the separation obtained in single permeation stages with idealized flow patterns inside the stage, including countercurrent, cocurrent, cross-flow and perfect mixing. An example is presented using the models of Stern and co-workers to show how the extent of separation varies with stage cut and area. The extent of separation clearly shows how the “goodness” of separation varies with stage cut and which stage cut represents the best separation. For the example used (the separation of air) the maximum extent of separation is significantly different for the different flow patterns. The effectiveness is in the order countercurrent > cross-flow > cocurrent > perfect mix.     

Fast separation of oligonucleotide and triplet repeat DNA on a microfabricated capillary electrophoresis device and capillary electrophoresis

A laser-induced fluorescence detection system coupled with a highly sensitive silicon-intensified target (SIT) camera is successfully applied to the imaging of a band for DNA fragment labeling by fluorescence dye in a microchannel, and to the visualizing of the separation process on a microfabricated chip. We demonstrated that an only 6 mm separation channel is sufficient for the separation of triplet repeat DNA fragment and DNA molecular marker within only 12 s. The separation using the microfabricated capillary electrophoresis device is confirmed to be at least 18 times faster than the same separation carried out by conventional capillary electrophoresis with 24.5 cm effective length. The use of a short capillary with 8.5 cm effective length is also efficient for fast separation of DNA; however, the microchip technology is even faster than capillary electrophoresis using a short capillary.     

Two-dimensional liquid chromatography of peptides: An optimization strategy

Summary An optimization strategy for the separation of a small number of peptides from a complex biological sample by two-dimensional liquid chromatography is presented. Ion-exchange chromatography is followed by reversed-phase separation. The ion-exchange separation is performed with a step gradient which admits a high sample load and simplifies instrumentation. The reversed-phase separation complements the first dimension with a different retention mechanism and higher resolution by linear gradient elution.Chromatographic theory is combined with experimental design to find separation conditions, for both dimensions, that allow the fastest gradient in the second dimension, giving short separation time, low detection limits and high load capacity. This is illustrated by the separation of a peptide from rat brain tissue, with a simple off-line arrangement. The strategy presented is useful in both analytical and preparative applications, and is widely applicable as it does not rely on special instrumentation or extensive knowledge of the sample.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Low-voltage driven control in electrophoresis microchips by traveling electric field.

This paper presents the use of a physical model and numerical simulation in the investigation of traveling electric fields on capillary electrophoresis (CE) chips. The principal material transport mechanisms of electrokinetic migration, ionic concentration, fluid flow, and diffusion are all taken into consideration. Traditionally, the high electric field strength required for the separation of biological samples by microfluidic devices has involved the application of high external voltages. In contrast, this study presents a proposal for samples separation by means of a moving electric field within a low voltage-driven CE chip. Under this proposal, the separation channel is partitioned into a series of smaller separation zones by means of electrode pairs. This paper considers two different electrode configurations, namely arranged along a single side of the separation channel, and arranged on two sides of the separation channel. The quality of the separation achieved with these two configurations is then compared with the traditional straight separation channel approach. The results confirm that the proposed method is successful in maintaining an adequate field strength for separation purposes in a low-voltage driven CE chip. Furthermore, it is determined that the best separation results are obtained using electrodes arranged along both sides of the separation channel.     

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.     

Separation of Anions of Organic Acids in Concentrated Solutions by Means of Capillary Isotachophoresis

The separation of a mixture containing anions of nine organic acids is investigated on an instrument for capillary isotachophoresis with an optical detector for the registration of boundaries. The separation is conducted in concentrated solutions of sodium salts. A counterflow is used during the separation.     

Very fast electrophoretic separation on commercial instruments using a combination of two capillaries with different internal diameters

A capillary formed by connecting a 9.7 cm‐long separation capillary with id 25 μm with an auxiliary 22.9 cm‐long capillary with id 100 μm (coupled capillary) was tested for electrophoretic separation at high electric field intensities. The coupled capillary was placed in the cassette of a standard electrophoresis apparatus. It was used in the short‐end injection mode for separation of a mixture of dopamine, noradrenaline, and adrenaline in a BGE of 20 mM citric acid/NaOH, pH 3.2. An intensity of 2.7 kV/cm was attained in the separation part of the capillary at a separation voltage of 30 kV, which is 2.9 times more than maximum intensity value attainable in a capillary with the same length with uniform id. At these high electric field intensities, the migration times of the tested neurotransmitters had values of 12.3–13.3 s and the attained separation efficiency was between 2350 and 2760 plates/s. It is thus demonstrated that an effective separation instrument ‐ a coupled capillary ‐ can be used for very rapid separation in combination with standard, commercially available instrumentation.     

Investigation of the separability of thaumatin by capillary electrophoresis

The electrophoretic behaviour of the highly basic protein thaumatin was explored in strongly acid (pH 2) and mildly acid (pH 4.5) separation systems using both bare and coated fused silica capillaries. The separation selectivity for thaumatin I, thaumatin II, and for other sample constituents was insufficient for their baseline separation at pH 2 in an uncoated capillary because the separation efficiency was markedly lower than is common in the electrophoretic separations of proteins. A separation selectivity higher by up to one order of magnitude has been reached at pH 4.5. A pronounced asymmetry of zones, which impaired resolution at this pH, was effectively suppressed by coating of the capillary wall with a polymer. In fact, adsorption on the capillary coating always plays a contributory role whenever a good separation of thaumatin constituents is attained. This indicates that electrochromatographic separation systems based on capillaries coated with the layer of either cationic or hydrophilic uncharged polymer hold promise for the development of methods for thaumatin analysis.     

离子液体在乙烯/乙烷和乙烯/乙炔分离中的应用

乙烯,作为石油化工行业的龙头原料,其高效回收分离具有重要的战略意义。离子液体作为一种结构可调控的新型绿色溶剂,在乙烯的回收分离中展现出巨大的应用前景。本文总结了近年来离子液体在乙烯/乙烷和乙烯/乙炔分离方面的研究进展,从溶剂吸收、膜吸收和与多孔材料相结合的吸附分离法等角度展开,系统地阐述了常规离子液体、功能化离子液体、聚离子液体等纯组分体系及多组分体系在不同分离方法中的研究现状,展望了离子液体在乙烯回收分离方面的应用前景和发展趋势。     

PDMS free-flow electrophoresis chips with integrated partitioning bars for bubble segregation

In this work, a microfluidic free-flow electrophoresis device with a novel approach for preventing gas bubbles from entering the separation area is presented. This is achieved by integrating partitioning bars to reduce the channel depth between electrode channels and separation chamber in order to obtain electrical contact and simultaneously prevent bubbles from entering the separation area. The three-layer sandwich chip features a reusable carrier plate with integrated ports for fluidic connection combined with a softlithographically cast microfluidic PDMS layer and a sealing glass slide. This design allows for a straightforward and rapid chip prototyping process. The performance of the device is demonstrated by free-flow zone electrophoretic separations of fluorescent dye mixtures as well as by the separation of labeled amines and amino acids with separation voltages up to 297 V.     

Continuous flow electrophoretic separation — Recent developments and applications to biological sample analysis

Continuous flow electrophoretic separation with continuous sample loading provides the advantage of processing volumes of any sizes, as well as the benefit of a real-time monitoring and optimization of the separation process. In addition, the spatial separation of the sample enables collecting multiple separated components simultaneously and in a continuous manner. The separation is usually performed in mild buffers without organic solvents and detergents (sample biological activity is retained) and it is carried out without usage of a solid support in the separation space preventing the interaction of the sample with it (high sample recovery). The method is used for the separation of proteins/peptides in proteomic applications, and its great applicability is to the separation of the cells, cellular organelles, vesicles, membrane fragments, and DNA. This review focuses on the electrophoretic separation performed in a continuous flow and it describes various electrophoretic modes and instrumental setups. Recent developments in methodology and instrumentation, the integration with other techniques, and the application to the biological sample analysis are discussed as well.     

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.     

Metrics of separation performance in chromatography. Part 1. Definitions and application to static analyses

Earlier introduced metrics of separation performance are described in a systematic way. After providing the definitions of the metrics suitable for a broad variety of applications, the study focuses on static analyses (isothermal GC, isocratic LC, etc.) and their general separation performance. Statistically expected number of resolved (adequately separated) single-component peaks is treated as the ultimate metric of general separation performance of chromatographic analysis. That number depends on the peak capacity of the analysis and the number of components in a test mixture. The peak capacity, in turn, depends on the separation capacity of a column and the lowest separation required by the data-analysis system for resolving poorly separated peaks. The separation capacity is a special case of a broader metric of the separation measure which is a function of column efficiency, solute separability, and the level of the solute interaction with a column stationary phase. The formulae for theoretical prediction of all these metrics for arbitrary pairs of peaks in static analyses are derived. To provide a better insight into the basic metrics of the separation performance, additional metrics such as the solute discrimination (relative difference in solute velocities), utilization of separability (solute discrimination per unit of their separability), specific separation (the separation per unit of separability), and others are defined and found for static analyses.     

Synchronized cyclic capillary electrophoresis using channels arranged in a triangle and low voltages

Synchronized cyclic capillary electrophoresis (SCCE) makes use of a closed loop separation channel by which the same sample can be separated during many cycles. This enables the repeated use of the same voltage for separations such that a high total voltage, and thus high efficiency, is obtained for the synchronized components. This can be accomplished by using any type of polygon geometry for the separation channel; and calculations of the available field and number of connections needed for polygons from 3 to 5 sides are presented. Triangular designs have the advantage of using the lowest number of wells. Such designs are described, with two additional features compared to that of earlier work: 1. voltage connections that are much shallower than the separation channel, to reduce losses and dispersion at the intersections; and 2. corners that are narrower than the separation channels to reduce dispersion in the turns. Experimental data is presented for the separation of a mixture of amino acids, and for a DNA separation in a polymeric sieving matrix. The DNA separation is most sensitive to the corner dispersion problem, which reduces the observed efficiency for that separation.     

The theory and practice of liquid-liquid partition chromatography of phenols

An equation is given for the design of liquid-liquid partition Chromatographie columns which relates the separation factors and column, characteristics with the number of theoretical plates required for a desired separation. This equation should be applicable to the separation of acids or bases when a buffered stationary phase is used, thus permitting a more rational approach to this technique.Using this approach a complete separation of the three isomeric cresols has been achieved. Methods are given for this determination and also for the determination of phenol in tar acid mixtures.     

Hydrate-based carbon dioxide capture from simulated integrated gasification combined cycle gas

The equilibrium hydrate formation conditions for CO2/H2 gas mixtures with different CO2 concentrations in 0.29 mol% TBAB aqueous solution are firstly measured.The results illustrate that the equilibrium hydrate formation pressure increases remarkably with the decrease of CO2 concentration in the gas mixture.Based on the phase equilibrium data,a three stages hydrate CO2 separation from integrated gasification combined cycle (IGCC) synthesis gas is investigated.Because the separation efficiency is quite low for the third hydrate separation,a hybrid CO2 separation process of two hydrate stages in conjunction with one chemical absorption process (absorption with MEA) is proposed and studied.The experimental results show H2 concentration in the final residual gas released from the three stages hydrate CO2 separation process was approximately 95.0 mol% while that released from the hybrid CO2 separation process was approximately 99.4 mol%.Thus,the hybrid process is possible to be a promising technology for the industrial application in the future.     

Characterization of various geometric arrangements of “air-assisted” flow gating interfaces for capillary electrophoresis

For connecting flow-through analytical methods with capillary electrophoresis, a chip working in the air-assisted flow gating interface regime is cast from poly(dimethylsiloxane). In the injection space, the exit from the delivery capillary is placed close to the entrance to the separation capillary. Prior to injecting the sample into the separation capillary, the background electrolyte is forced out of the injection space by a stream of air. In the empty space, a drop of the sample with a volume of <100 nL is formed between the exit from the delivery capillary and the entrance into the separation capillary, from which the sample is injected hydrodynamically into the separation capillary. After injection, the injection space is filled with BGE, and the separation can be begun. Three geometric variants for the mutual geometric arrangement of the delivery and separation capillaries were tested: the delivery capillary is placed perpendicular to the separation capillary, from either above or below, or the capillaries are placed axially, that is, directly opposite one another. All of the variants are equivalent from the analytical and separation efficiency viewpoints. The repeatability expressed by RSD is up to 5%. The tested flow gating interface variants are also suitable for continuous and discontinuous sampling at flow rates of the order of units of μL/min. The developed instrument for sequential electrophoretic analysis operates fully automatically and is suitable for rapid sequential monitoring of dynamic processes.     

Rapid analysis of isomeric exogenous metabolites by differential mobility spectrometry-mass spectrometry

The direct separation of isomeric glucuronide metabolites from propranolol dosed tissue extracts by differential mobility spectrometry-mass spectrometry (DMS-MS) with the use of the polar gas-phase chemical modifier acetonitrile was demonstrated. The DMS gas-phase separation was able to resolve the isomeric metabolites with separation times on the order of milliseconds instead of minutes which is typically required when using pre-ionization chromatographic separation methods. Direct separation of isomeric metabolites from the complex tissue extract was confirmed by implementing a high-performance liquid chromatography (HPLC) separation prior to the DMS-MS analysis to pre-separate the species of interest. The ability to separate isomeric exogenous metabolites directly from a complex tissue extract is expected to facilitate the drug development process by increasing analytical throughput without the requirement for pre-ionization cleanup or separation strategies.