Influence of the Modifier Type and its Concentration on Electroosmotic Flow of the Mobile Phase in Pressurized Planar Electrochromatography.

The aim of this work was to find a relationship between electroosmotic flow (EOF) velocity of the mobile phase in pressurized planar electrochromatography (PPEC) and physicochemical properties like zeta potential, dielectric constant, and viscosity of the mobile phase as well as its composition. The study included different types of organic modifiers (acetonitrile, methanol, ethanol, acetone, formamide, N-methylformamide and N,N-dimethylformamide) in the full concentration range. In all experiments, chromatographic glass plates HPTLC RP-18 W from Merck (Darmstadt) were used as a stationary phase. During the study we found that there is no linear correlation between EOF velocity of the mobile phase and single variables such as zeta potential or dielectric constant or viscosity. However, there is quite strong linear correlation between EOF velocity of the mobile phase and variable obtained by multiplying zeta potential of the stationary phase-mobile phase interface, by dielectric constant of the mobile phase solution and dividing by viscosity of the mobile phase. Therefore, it could be concluded that the PPEC system fulfilled the Helmholtz-Smoluchowski equation.

Equipment and preliminary results for orthogonal pressurized planar electrochromatography.

We report combination of overpressured layer chromatography (OPLC) and pressurized planar electrochromatography (PPEC) techniques into a single technique in which both OPLC and PPEC processes proceed simultaneously and orthogonally. The separation process with this new technique is performed in adsorbent layer of a chromatographic plate, which is equipped with special sealing margin on its whole periphery and closed under pressure in special chamber. We have named this separation technique as orthogonal pressurized planar electrochromatography (OPPEC). Examples of analytical and micropreparative (continuous) OPPEC separations are demonstrated.

Pressurized planar electrochromatography.

Theoretical backgrounds, development, examples of separations, constructional details and principle of action of devices of pressurized planar electrochromatography (PPEC) are presented. Development of the mode is described in respect of operating variables (composition of the mobile phase, pressure exerted on adsorbent layer, mobile phase flow velocity, temperature of separating system, etc.) influencing separation efficiency (kinetic performance, repeatability, separation time). Advantages of PPEC such as high kinetic performance, short separation time and different separation selectivities, especially relative to conventional thin-layer chromatography, are described. Examples of two-dimensional separations are demonstrated to show high separation potential of the mode when combined with conventional thin-layer chromatography (TLC). The PPEC mode is in infancy stage of development, so its challenges are presented as well.

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.

Influence of sample application mode on performance of pressurized planar electrochromatography in completely closed system.

Three modes of sample application on the chromatographic plate are applied at present investigations of pressurized planar electrochromatography (PPEC) systems taking into special attention their influence on performance of the separating system. These modes are as follows: application of the sample solution directly on the chromatographic plate with microsyringe, deposition of sample solution on scrap of adsorbent layer followed by location oft this scrap on the chromatographic plate, application of the sample solution with commercially available aerosol applicator. These modes were combined with prewetting procedures of the chromatographic plates which lead to an accomplishment of equilibration of the stationary phase-mobile phase system. The plots of plate height versus linear flow rate of the mobile phase are presented for PPEC systems for the first time. The best separation performance has been obtained in PPEC system when prewetting of the chromatographic plate followed the sample application with commercially available aerosol applicator. The higher repeatability of migration distance of the solute bands has been obtained in PPEC experiments when the sample application was followed by prewetting the chromatographic plate in comparison to the experiments when these operations were performed in reversed order.

Apparatus for pressurized planar electrochromatography in a completely closed system.

Pressurized planar electrochromatography (PPEC) is the mode which offers much higher separation efficiency in comparison to conventional planar chromatography, including both higher performance and much higher speed of separation. In this paper, we present a new device for performing PPEC in which the whole area of the chromatographic plate is pressurized. Both electrodes (anode and cathode) are washed with the mobile phase during the experiment, which prevents gas bubbles from collection in the region of the electrodes. This device enables directly controlling the flow rate of the mobile phase during the electrochromatography process. Mobile phase control offers the possibility of researching the influence of various properties of the PPEC system on separation efficiency. One important relationship to investigate is plate height vs mobile phase flow rate. This relationship helps to choose the optimal value of the mobile phase flow rate during the separation process. Considerable difference in shape of this relationship is demonstrated for conventional planar chromatography plates and high performance planar chromatography plates. Examples of the influence of some properties of the separating system on flow rate of the mobile phase are demonstrated, such as the buffer concentration in the mobile phase, the pH value of the buffer solution of the mobile phase, the type of chromatographic plate, and the voltage applied to the electrodes.