A variant of circular thin-layer chromatography with a forced flow of the mobile phase produced by an electroosmotic pump

A new variant of circular thin-layer chromatography (TLC) with a closed sorption layer in which a forced flow of the mobile phase was produced and controlled by an external electroosmotic pump placed at the center of a TLC plate was suggested. It was shown experimentally that the method operated properly and could be used in planar chromatography.     

Quasi-thin layer chromatography with forced flow of the mobile phase in microchannels packed with a sorbent

A version of the thin-layer chromatography with forced flow of the mobile phase in microchannels packed with a sorbent is proposed. The dependences of retention parametersR _f and the number of theoretical plates in the course of the elution of hydrophilic dyes (naphthol red and methyl red) on the eluent (propan-2-ol) pressure and developing time were studied. The method can be of interest as a simplified version of the forced-flow TLC and would be useful as a micropilot technique for liquid chromatography. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1538–1539, August, 1997.     

The use of vacuum in thin-layer chromatography with a forced flow of the mobile phase on plates with covered polymer layer

A new version of TLC with a forced flow of the mobile phase has been suggested. The variant involves the use of a TLC plate, the sorption layer on which is covered with a polymer film, and evacuation as an additional driving force for the mobile phase. The advantages of the new method were analyzed; the velocity coefficient of the movement of the mobile phase front was found to be linearly dependent on the rarefaction at the end of the plate.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1143–1146, May, 1996.     

New versions of circular thin-layer chromatography on plates with a closed sorption layer

New versions of circular thin-layer chromatography (corner TLC and lateral TLC) with a closed sorption layer are proposed, studied, and compared with traditional methods of linear and circular TLC. The use of a closed sorption layer in the new versions of circular chromatography is demonstrated to reduce the duration of separation (by 15–20%) while lowering the efficiency of separation negligibly. The feasibility of TLC with a closed sorption layer is demonstrated for the determination of highly volatile compounds.     

Influence of flow parameters of the mobile phase on the retention and thermodynamic characteristics of sorption in gas-liquid chromatography

The influence of the flow parameters of the mobile phase (flow rate and mean pressure in the column) on the retention and thermodynamic characteristics of sorption in gas-liquid chromatography is studied experimentally. Conditions are formulated under which the chromatographic process can be described in terms of the theory of equilibrium gas-liquid chromatography with an ideal gas as the mobile phase and the distribution of the sorbate between phases is not affected by the presence of a weakly sorbed carrier gas.     

Liquid adsorption chromatography with a two-component mobile phase : I. Effects of non-ideality of the mobile phase

Analytical expressions for the distribution coefficient of a chromatographed compound, taking into account the non-ideality of a two-component mobile phase, have been derived in terms of Snyder's theory of liquid adsorption chromatography and the theory of liquid adsorption formulated by Everett and Myers. Model calculations have been made by assuming regularity of the mixed mobile phase.     

Control of electroosmotic flow by polymer coating: effects of the electrical double layer

We report on the molecular dynamics simulations of electroosmotic flow control by polymer coating. We show that polymer coating modulates the flow by rendering drag to fluids and by changing the ion distribution and ion-surface interactions in the electrical double layer. Because of the latter two effects, the polymer coating can even enhance the flow under certain conditions. Identifying the effects of these processes is crucial for the rational design of polymer coating for electroosmotic flow control.     

Characterization of the SDS-induced electroosmotic flow in micellar electrokinetic chromatography with cationic polyelectrolyte-coated capillaries

Manipulation of the EOF is essential for achieving optimal separations by MEKC. In this paper, we present an extensive investigation of the effect of common experimental conditions on the EOF observed in a capillary coated with poly(diallyldimethylammonium chloride) (PDADMA) polyelectrolyte under MEKC conditions. It was found that highly reproducible cathodal EOF is achieved approximately at or just below the conditional CMC value of SDS in the electrolytes used. At concentrations of SDS greater than the CMC the EOF is independent of pH. The impact of common organic modifiers (ACN, methanol, urea, beta-CD and nonionic surfactant) on the EOF behavior in both a PDADMA-coated capillary and a bare silica capillary is compared. The suppressing effect of organic modifiers on the EOF is much stronger for coated capillary indicating that these compounds additionally reduce the negative charge density on the capillary surface due to alteration of the surfactant coating.     

Design of mobile phase composition for liquid chromatography with an internal pH gradient

Summary A method is suggested for calculating the mobile phase composition for ion exchange chromatography with an internal pH gradient. An internal pH gradient of the desired steepness can be achieved providing the titration curve of the sorbent is known. The procedure has been verified by use in the design of a mobile phase composed from few anionic buffers for generation of internal pH gradient on a microcolumn packed with a cation exchanger with carboxylic functional groups.     

Overpressured layer chromatography in comparison with thin-layer and high-performance liquid chromatography for the determination of coumarins with reference to the composition of the mobile phase

The retention behaviour of fifteen closely related coumarins in normal-phase overpressured layer chromatography (OPLC) was studied with the aim of comparing the retentions with those in normal-phase thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) when optimization of the mobile phase was carried out according to the PRISMA system. The mobile phase optimization was carried out on TLC plates in unsaturated chambers. The resulting mobile phases were transposed to off-line, non-equilibrated OPLC and further to HPLC. The retention in TLC was measured at 37 selectivity points and in OPLC and HPLC at 13 points. Capacity factors (k′) and separation factors () were calculated in order to study the retention behaviour in the different systems. Two- and three-dimensional evaluations of k′ against selectivity points showed similar retention behaviours for the coumarins in TLC, OPLC and HPLC. The values for TLC, OPLC and HPLC showed similar patterns in the three-dimensional evaluations. The retention behaviour at different solvent strengths was also examined. According to quadratic regression, k′ showed a dependence on the change in solvent strength. OPLC, which can be considered as a “planar column” technique, and TLC are closely related methods, whereas HPLC shows a different behaviour in the elution process with regard to solvent strength.     

Version of conventional thin-layer chromatography with a contact-covered sorption layer (Chamberless TLC)

A new version of TLC with a covered sorbent layer and without a free vapor volume is proposed along with a simple removable device to implement this version. The new TLC version has been tested experimentally using plates with silica gel on an aluminum substrate and ethanol, a water-24% aqueous ammonia (30:0.1) mixture, and an acetonitrile-ethanol (10:1) mixture as the mobile phases. The proposed TLC version shortens the experiment duration by 10–30% in comparison with conventional TLC; in this case, the efficiency can either slightly increase or slightly decrease. The consumption of the mobile phase and its evaporation to the environment are reduced.     

Influence of mobile phase composition on electroosmotic flow velocity, solute retention and column efficiency in open-tubular reversed-phase capillary electrochromatography

The effects of some experimental parameters, such as the volume fraction and type of organic modifier in the mobile phase, and the concentration, type and pH of the buffer on the electroosmotic flow velocity, the retention behavior of test solutes, and the column efficiency have been investigated in capillary electrochromatography (CEC) using an open-tubular column of 9.60 microm I.D. with a porous silica layer chemically modified with C18 as stationary phase. The retention of a group of polycyclic aromatic hydrocarbons (PAHs) used as a test mixture varied significantly by changing the organic modifier content in the hydroorganic mobile phase according to the reversed-phase-like selectivity of the stationary phase. In addition, an increase in the percentage of organic modifier resulted in a slight increase in the linear velocity of the EOF. On the other hand, when the phosphate buffer concentration was increased over the range 1-50 mM, the electroosmotic mobility fell dramatically, the retention of the solutes decreased steadily, and the plate height showed a significant increase. The results obtained with phosphate, trishydroxymethylaminomethane or 2-morpholinoethanesulfonic acid as buffers were similar when pH remained constant. Optimization in CEC was essential to achieve further enhancement of separation performance, because the analysis time and separation resolution are essentially affected when varying operating parameters. Separations of seven PAHs with more than 100000 plates are presented within 4 min analysis time.     

Influence of the mobile phase on salmon calcitonin analysis by reversed-phase liquid chromatography

The retention properties of calcitonins on a reversed-phase column are examined using salmon calcitonin as the model compound. The effect of the concentration of organic modifier, buffer strength, pH of the mobile phase, and ion-pair reagent are studied. In the absence of an ionic modifier in the eluent the calcitonin peak shapes are not symmetrical. The addition of 0.1% trifluoroacetic acid (TFA), however, results in good peak characteristics without the need to add nonvolatile salts. The retention of the calcitonins was found to be very sensitive to the concentration of the organic modifier (acetonitrile) present in the mobile phase. A change of pH between 2 and 5 has only a slight effect of the k' of salmon calcitonin, but the k' increases significantly at higher pH values. The addition of a phosphate buffer to the mobile phase and an increase in the buffer concentration (0-0.2 M) causes a decrease in the retention of salmon calcitonin. Evidence shows that reproducible, quantitatively measurable data can be obtained using reversed-phase chromatography if the ion-pairing reagent and organic modifier concentrations are carefully controlled. The system also shows a good selectivity for the calcitonin series. Therefore, both highly selective methods (qualitative) as well as quantitative methods for analytical, pharmaceutical, and manufacturing use can be developed by adjusting the high-performance liquid chromatography (HPLC) conditions as discussed.     

Over-pressure TLC variant on a plate with an enclosed sorbent layer

An over-pressure TLC variant with an enclosed sorbent layer and forced flow of the mobile phase was suggested. A simple new type device for its realization was developed.Translated from Izvestiya Akademioi Nauk. Seriya Khimicheskaya, No. 3, pp.771–773, March, 1996.