A Modified Device for Pressurized Planar Electrochromatography and Preliminary Results with On-Line Sample Application

Pressurized planar electrochromatography (PPEC) is a separating technique in which an electric field is applied to force the mobile phase movement through a porous media (electroosmotic effect). High separation efficiency, fast separations and changes in separation selectivity in comparison to liquid chromatography, especially thin layer chromatography (planar chromatography, TLC), are features of this technique. Constructional methodological challenges to PPEC are obstacles to its development and application in laboratory practice. In this article, an attempt to overcome the challenges related to device construction and sample application/injection is described. The introduced device enables both prewetting of the adsorbent layer and electrochromatogram development with a single PPEC device. It also enables simultaneous application/injection of six samples on a chromatographic plate in a stream of the mobile phase (on-line application/injection). In addition, the PPEC chamber was equipped with a thermostat. The device is characterized by an impressive throughput in comparison to the other planar technique, TLC/HPTLC. Although the developed device still needs improvement, it is, in our opinion, a considerable step toward possible automation of this planar separation technique.     

Pressurized planar electrochromatography,high-performance thin-layer chromatography and high-performance liquid chromatography—Comparison of performance

Kinetic performance, measured by plate height, of High-Performance Thin-Layer Chromatography (HPTLC), High-Performance Liquid Chromatography (HPLC) and Pressurized Planar Electrochromatography (PPEC) was compared for the systems with adsorbent of the HPTLC RP18W plate from Merck as the stationary phase and the mobile phase composed of acetonitrile and buffer solution. The HPLC column was packed with the adsorbent, which was scrapped from the chromatographic plate mentioned. An additional HPLC column was also packed with adsorbent of 5 μm particle diameter, C18 type silica based (LiChrosorb RP-18 from Merck). The dependence of plate height of both HPLC and PPEC separating systems on flow velocity of the mobile phase and on migration distance of the mobile phase in TLC system was presented applying test solute (prednisolone succinate). The highest performance, amongst systems investigated, was obtained for the PPEC system. The separation efficiency of the systems investigated in the paper was additionally confirmed by the separation of test component mixture composed of six hormones.     

Separation of Some Aromatic Amino Acid Enantiomers with Pressurized Planar Electrochromatography and TLC

Influence of buffer pH, buffer concentration and ratio of methanol to acetonitrile in ternary mobile phase on migration distance of enantiomers of phenylalanine, tyrosine and DOPA in pressurized planar electrochromatography (PPEC) and thin-layer chromatography (TLC) systems is presented and compared. The applied operating variables in PPEC system more strongly influence on separation selectivity of investigated solutes than those in TLC one. Higher separation efficiency of PPEC system relative to TLC one is also demonstrated.     

Preliminary results for 2‐D separation with high‐performance thin‐layer chromatography and pressurized planar electrochromatography

Preliminary results of 2‐D separation of test dye mixture using high‐performance thin‐layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC) are demonstrated. The advantage of 2‐D HPTLC/PPEC separation is based on different separation selectivities obtained in both HPTLC and PPEC systems. HPTLC RP18 W plates of 5×20 cm from Merck were used in the investigations. In the first dimension, a HPTLC process was performed using 5 cm length of the plate and in the second dimension PPEC separation was obtained applying plate of 20 cm length. PPEC process followed prewetting the chromatographic plate with sample zones on it, which were partly separated after first dimensional (HPTLC) separation. In the experiments, the modified version of PPEC device for 20 cm long chromatographic plate and the reservoir for prewetting the adsorbent layer were applied.     

High performance stationary phases for planar chromatography

The kinetic performance of stabilized particle layers, particle membranes, and thin films for thin-layer chromatography is reviewed with a focus on how layer characteristics and experimental conditions affect the observed plate height. Forced flow and pressurized planar electrochromatography are identified as the best candidates to overcome the limited performance achieved by capillary flow for stabilized particle layers. For conventional and high performance plates band broadening is dominated by molecular diffusion at low mobile phase velocities typical of capillary flow systems and by mass transfer with a significant contribution from flow anisotropy at higher flow rates typical of forced flow systems. There are few possible changes to the structure of stabilized particle layers that would significantly improve their performance for capillary flow systems while for forced flow a number of avenues for further study are identified. New media for ultra thin-layer chromatography shows encouraging possibilities for miniaturized high performance systems but the realization of their true performance requires improvements in instrumentation for sample application and detection.     

薄层电色谱技术的研究进展

薄层电色谱技术将电场力的作用引入薄层色谱的分离过程中,具有分离时间短、分辨率高等特点,将可能在物质分析分离中发挥重要作用.本文介绍了薄层电色谱仪器装置的设计、固定相和流动相的类型、薄层电色谱的应用等内容,总结了目前的研究工作中存在的主要问题,并展望了该技术未来的发展趋势,还介绍了与薄层电色谱有相似的毛细管电色谱和自由流电泳技术.引文献50篇.     

Progress in planar electrochromatography

Developments in planar electrochromatography in open (PEC) and closed (PPEC) systems are reviewed. The discussion focuses on progress in chamber construction for planar electrochromatography, separating system performance, equilibration of the PPEC process, separation time and selectivity, and the general advantages, disadvantages and prospects of this separation mode. Presented at the 11th International Conference on Chemistry and the Environment, 9–12 September 2007, Torum, Poland.     

Morphological modification of nanostructured ultrathin-layer chromatography stationary phases

Ultrathin-layer chromatography (UTLC) provides the high sensitivities and rapid separations over short distances desirable in many analytical applications. The dependence of these performance benefits on UTLC layer microstructure motivates continued stationary phase engineering efforts. A new method of modifying the elution behaviours of nanostructured thin film UTLC stationary phases is investigated in this report. Macroporous normal phase silica thin films ～5 μm thick were fabricated using glancing angle deposition (GLAD). Reactive ion etching (RIE) and a subsequent annealing treatment modified stationary phase morphology to tune migration velocity, analyte retention, and overall separation performance. Combining this technique with a RIE shadow mask enabled fabrication of adjacent concentration and separation zones with markedly different elution properties. Although produced using an entirely new approach, GLAD UTLC concentration zone media behaved in a manner consistent with traditional thin-layer chromatography (TLC) and high-performance TLC (HPTLC) concentration zone plates. In particular, these new media focused large volume, low concentration dye mixture spots into narrow bands to achieve high-quality separations. The described approach to modifying the morphology and resultant elution behaviours of nanostructured stationary phases expands the capabilities of the GLAD UTLC technique.     

硅胶色谱柱的亲水作用保留机理及其影响因素

亲水作用色谱（HILIC）是替代反相色谱（RPLC）分离强极性及亲水性化合物的另一色谱模式,其分离机理与RPLC有很大不同,具有和RPLC互补的选择性。在HILIC模式中,采用正相色谱（NPLC）中的极性固定相及含高浓度有机溶剂（通常为乙腈）的水溶液为流动相。硅胶是开发最早、研究最为深入及应用最为广泛的HILIC固定相,本文介绍了硅胶色谱柱的HILIC保留机理,详细概述了操作条件如硅胶柱类型、流动相组成及柱温对HILIC分离的影响,并对硅胶填料色谱柱的HILIC模式的发展方向与应用前景进行了展望。     

Spot and Mobile-Phase Front Anomalies in Planar (Thin-Layer) Chromatography

The advantages and variations of thin-layer chromatography are described in detail. The displacement mode of development is generated in a relatively short distance, and the fully developed displacement train concentrates sample components even from an elongated spot. Two-dimensional TLC using both elution and displacement thin-layer chromatography enables excellent separation of spots; results from 2D TLC cannot, however, be derived directly from two one-dimensional runs. Secondary mobile-phase fronts occur because of the dry state of stationary phase, which absorbs the mobile phase. Occasional problems with the reproducibility of R_F values arise because of adsorption of the mobile phase components by the dry stationary phase and evaporation at the solvent front. The use of 2D TLC in pharmacognosy enables separation of the components and also helps in the planning of preparative-scale separations by classical column chromatography and/or HPLC.     

Planar chromatography at the turn of the century.

An overview of the state-of-the-art of modern thin-layer chromatography (planar chromatography) is presented with emphasis on the complementary features of thin-layer and column liquid chromatographic separations. The reasons for selecting thin-layer chromatography for a particular analysis are identified by its attributes: a disposable stationary phase; simultaneous parallel separations; static detection free of time constraints; storage device for chromatographic information; all sample components are observed in the chromatogram. Future prospects for improved separation performance in TLC using zone refocusing, forced flow and electroosmotic flow methods are discussed as well as increasing zone capacity by using two-dimensional development and coupling to column chromatographic methods. Advances in coupling thin-layer chromatography with spectroscopic methods for structural elucidation are also considered. Finally, some predictions are made for how thin-layer chromatography will be practiced in the future.     

Feasibility of ultra high performance supercritical neat carbon dioxide chromatography at conventional pressures

The implementation of columns packed with sub-2 μm particles in supercritical fluid chromatography (SFC) is described using neat carbon dioxide as the mobile phase. A conventional supercritical fluid chromatograph was slightly modified to reduce extra column band broadening. Performances of a column packed with 1.8 μm C18-bonded silica particles in SFC using neat carbon dioxide as the mobile phase were compared with results obtained in ultra high performance liquid chromatography (UHPLC) using a dedicated chromatograph. As expected and usual in SFC, higher linear velocities than in UHPLC must be applied in order to reach optimal efficiency owing to higher diffusion coefficient of solutes in the mobile phase; similar numbers of theoretical plates were obtained with both techniques. Very fast separations of hydrocarbons are presented using two different alkyl-bonded silica columns.     

Separation of four mixtures of pesticides by pressurized planar electrochromatography (PPEC)

Examples of separations of four mixtures of pesticides by pressurized planar electrochromatography (PPEC) under different operating conditions are presented. The samples were separated on a prewetted RP-18W chromatographic plate in a system with acetonitrile-buffer as the mobile phase. A potential of 2.3 kV was applied to a 10 cm long plate to create the electric field. Reproducible retention of pesticides was obtained during PPEC in the closed system when the sorbent layer of the plate was prewetted and equilibrated with the mobile phase. The reported separations of pesticides by PPEC are over 10 times faster than the corresponding separations by TLC.     

液相色谱塔板高度方程的统一形式

研究了色谱分离过程中物质的径向扩散和流动相发热对柱效能的影响。从热传导方程出发,运用色谱过程动力学原理推导了包括考虑流动相径向扩散、色谱柱发热影响的液相色谱塔板高度方程：

该方程概括了高效液相色谱（HPLC）、超高效液相色谱（UPLC）、毛细管电色谱（CEC）和消滞留层液相色谱（ESFLC）塔板高度与各种因素的关系。方程最后一项代表了径向扩散和柱发热对塔板高度的贡献。当流动相线速度较低且柱内径较细时,流动相摩擦生热和径向扩散对塔板高度的贡献趋近于零,塔板高度方程还原成Horvath和Lin的方程;当流动相线速度较高时,由于流动相摩擦生热,柱轴心与边缘温差增加,导致流动相线速度径向分布差异,使得柱效率降低。柱轴心与边缘的温差与流动相线速度平方成正比。该文指出,在流动相高线速度情况下,液相色谱的柱效率与柱内径密切相关,采用细内径柱有利于实现高速与高效率;过高的流动相线速度将导致色谱柱效率崩溃。     

Closed-Loop Recycling Dual-Mode Counter-Current Chromatography with Specified Sample Loading Durations: Modeling of Preparative and Industrial-Scale Separations

We previously reported on a new counter-current chromatography (CCC) operating mode called closed-loop recycling dual-mode counter-current chromatography (CLR DM CCC), which incorporates the advantages of closed-loop recycling (CLR) and dual-mode (DM) counter-current chromatography and includes sequential separation of compounds in the closed-loop recycling mode with the mobile x-phase and in the inverted-phase counter-current mode with the mobile y-phase. The theoretical analysis of several implementations of this separation method was carried out under impulse sample injection conditions. This study is dedicated to the further development of CLR DM CCC theory applied to preparative and industrial separations, where high-throughput operation is required. Large sample volumes can be loaded via continuous loading within a specified time. To simulate CLR DM CCC separations with specified sample loading durations, equations are developed and presented in “Mathcad” software.     

磷酸钛离子交换薄层色谱分离无机离子(英文)

The chromatographic behavior of 30 inorganic cations has been studied on thin layers of titanium phosphate ion-exchanger using several aqueous,organic and mixed mobile phases.The separation of one ion from several other ions and also ternary and binary separations have been developed.Some important analytical separations are reported.The effect of pH of the mobile phase on retention factor(Rf)values of the cations in the presence of complex-forming anion along with the separation power of the ion-exchanger were studied.This ion-exchanger exhibits high sorption capacity and varying selectivity towards metal ions and makes it a suitable stationary phase in thin layer chromatography.     

Enhanced‐fluidity liquid chromatography using mixed‐mode hydrophilic interaction liquid chromatography/strong cation‐exchange retention mechanisms

The potential of enhanced‐fluidity liquid chromatography, a subcritical chromatography technique, in mixed‐mode hydrophilic interaction/strong cation‐exchange separations is explored, using amino acids as analytes. The enhanced‐fluidity liquid mobile phases were prepared by adding liquefied CO₂ to methanol/water mixtures, which increases the diffusivity and decreases the viscosity of the mixture. The addition of CO₂ to methanol/water mixtures resulted in increased retention of the more polar amino acids. The “optimized” chromatographic performance (achieving baseline resolution of all amino acids in the shortest amount of time) of these methanol/water/CO₂ mixtures was compared to traditional acetonitrile/water and methanol/water liquid chromatography mobile phases. Methanol/water/CO₂ mixtures offered higher efficiencies and resolution of the ten amino acids relative to the methanol/water mobile phase, and decreased the required isocratic separation time by a factor of two relative to the acetonitrile/water mobile phase. Large differences in selectivity were also observed between the enhanced‐fluidity and traditional liquid mobile phases. A retention mechanism study was completed, that revealed the enhanced‐fluidity mobile phase separation was governed by a mixed‐mode retention mechanism of hydrophilic interaction/strong cation‐exchange. On the other hand, separations with acetonitrile/water and methanol/water mobile phases were strongly governed by only one retention mechanism, either hydrophilic interaction or strong cation exchange, respectively.     

Porous Monoliths: Stationary Phases of Choice for High Performance Liquid Chromatography in Various Formats

 Modern porous monoliths have been conceived as a new class of stationary phases for high performance liquid chromatography (HPLC) in classical columns in the early 1990s and later extended to the capillary format. These monolithic materials are prepared using simple processes carried out in an external mold (inorganic monoliths) or within the confines of the column (organic monoliths and all capillary columns). These methods afford macroporous materials with large through-pores that enable applications in a rapid flow-through mode. Since all the mobile phase must flow through the monolith, the convection considerably accelerates mass transport within the monolithic separation medium and improves the separations. As a result, the monolithic columns perform well even at very high flow rates. The applications of monolithic capillary columns are demonstrated on numerous separations in the HPLC mode.     

A review of advances in two-dimensional thin-layer chromatography

Although there are many simple thin-layer chromatography (TLC) separations, many more are complex and involve more than a few components, that means having to use special high-performance TLC (HPTLC) plates or microspotting or banding devices to increase its resolving power if developing in only one direction. However, adding a second development to perform two-dimensional TLC (2D TLC) allows even better resolution of complex samples. This is because different modes of chromatography are being invoked by the use of one stationary phase with two mobile phases, bilayer plates, graft TLC, or multidimensional TLC. This paper is a review of recent applications that have benefitted from using 2D TLC in its various forms. They were chosen for their variety of sample types as well as the unique choices of plates and/or mobile phases made by the researchers to yield improved separations.     

Behavior of peptides and computer-assisted optimization of peptides separations in a normal-phase thin-layer chromatography system with and without the addition of ionic liquid in the eluent

The addition of an ionic liquid into the mobile phase appeared to be useful in optimization of chromatographic separation of peptides. Different behavior of peptides in thin-layer chromatography (TLC) was observed after addition of 1-ethyl-3-methylimidazolium tetra fluoroborate to the eluent in comparison to the system without the ionic liquid. Nonlinear dependence of the retention coefficient, R(M), of peptides on the volume percentage of acetonitrile in the eluent was found in normal-phase TLC with and without immidazolium tetra fluoroborate in the mobile phase. In general, R(M) increased with increasing concentration of acetonitrile. In TLC systems without the ionic liquid, R(M) can be described well with a quadratic function. On the other hand, in a TLC system with an ionic liquid as the additive to the mobile phase, the retention behavior is better described with a third-degree polynomial function. The potential usefulness of ionic liquids for optimization of separation of peptides was demonstrated. Optimization of the separation conditions was supported by a commercially available computer program.