Forced-flow Planar Chromatography Research Articles

Forced-flow planar chromatography in the rear view mirror.

Mobile phase progress in planar stationary phase can be evoked by either external or internal forces. An internal force is capillarity, while gravity, electric field, a pump and centrifugal forces belong to external forces. Overpressured layer chromatography gives a widely used special chapter of forced-flow planar chromatography, a special bridge between high-performance liquid column chromatography and thin-layer chromatography (TLC). A simple and special rule characterizes the progress of mobile phase. Optimal efficiency is composed by the doubled effect of flow resulting from the pump-forced mobile phase (convex profile of laminar flow) and capillary forces on the dry stationary phase (concave laminar flow). This review describes the most important aspects of forced-flow TLC, including how the set-ups are developed and also the progress of detection methods used.

Retention characteristics of octadecylsiloxane-bonded silica and porous polymer particle-loaded membranes for solid-phase extraction

Forced-flow planar chromatography was used to determine the kinetic and retention properties of an octadecylsiloxane-bonded, silica-based, particle-loaded membrane used for solid-phase extraction. The sorbent was heavily loaded with bonded phase resulting in a small intraparticle porosity. The large plate height and flow resistance indicates a heterogeneous particle size distribution for the membrane with a significant fraction of below average size particles. The hydrophobicity and silanophilic indexes and system constants in the solvation parameter model indicate similar retention properties to a common octadecylsiloxane-bonded silica cartridge sorbent under identical mobile phase conditions. The dimensional instability of a porous polymer particle-loaded membrane prevented its evaluation by forced-flow planar chromatography using the overpressured development chamber. Breakthrough volumes were determined for the porous polymer membrane under typical sample processing conditions for a number of solutes with varied properties and fitted to a solvation parameter model. A comparison to data previously obtained for an octadecylsiloxane-bonded, silica-based, particle-loaded membrane (Bakerbond) indicated that ease of cavity formation favors retention by the octadecylsiloxane-bonded silica particle-loaded membrane for non-polar and weakly polar analytes compared to the porous polymer particle-loaded membrane. Significantly larger breakthrough volumes, however, are obtained on the porous polymer particle-loaded membrane for polar analytes. The porous polymer sorbent competes more effectively with water in dipole-type interactions and as a hydrogen-bond acid. A solvent effect is speculatively suggested as the origin of the porous-polymer sorbent's favorable retention of hydrogen-bond bases compared to the octadecylsiloxane-bonded, silica-based, material.

Sampling characteristics of octadecylsiloxane-bonded silica particle-embedded glass fiber discs for solid-phase extraction

Forced flow planar chromatography was used to characterize the physical and retention properties of an octadecylsiloxane-bonded particle-embedded glass fiber medium used for solid-phase extraction. The carbon loading, intraparticle porosity, binding capacity, and hydrophobicity index indicate that the medium has a large volume of bonded phase essentially filling the pore volume. The interparticle porosity and specific permeability indicate favorable flow characteristics. The flow resistance parameter and the diameter of the largest pore by the bubble method are consistent with a macroscopic homogeneous medium structure free of holes and channels. The silanophilic index indicates a significant concentration of accessible silanol groups and/or other strong hydrogen-bond acid sites. A comparison of retention characteristics to a common cartridge sorbent using the solvation parameter model indicated that the cartridge sorbent had a more favorable cavity term for retention but the particle-embedded glass fiber medium was more competitive with the sample solvent, water-methanol (99:1), for the retention of polar compounds with significant dipole-type interactions and those behaving as hydrogen-bond bases. The physical and retention properties of the particle-embedded glass fiber medium confirm its suitability for use in solid-phase extraction.

Investigation of the kinetic properties of particle-loaded membranes for solid-phase extraction by forced flow planar chromatography

Planar chromatography with forced-flow development is sued to characterize the kinetic and some thermodynamic properties of octadecylsilanized silica particle-loaded membranes intended for use in solid-phase extraction. The kinetic properties determined include the membrane porosity (e T =0.52, e u =0.37, and e I =0.15), membrane flow resistance (specific permeability -2.5×10 -14 m 2 , O=1000-1250), apparent particle size (dp=7.7 μm), and the coefficients for the van Deemter and Knox equations (H min =56 μm, u opt =0.13 mm/s, h min =7, and v opt =0.75)

Planar chromatography: Current status and future perspectives in pharmaceutical analysis (short review) — II. Special techniques and future perspectives in planar chromatography

The state of the art of various special analytical planar chromatographic methods is summarized especially for forced-flow planar chromatography (FFPC), overpressured-layer chromatography (OPLC) and rotation planar chromatography (RPC) as well as for the automated multiple development (AMD) technique. The connection between analytical planar and column liquid chromatographic methods and the identification of separated compounds with chromatographic and spectroscopic data are summarized. Some aspects of future perspectives, such as parallel connected multi-layer FFPC and long distance OPLC (LD-OPLC) are given. A combination of OPLC with the AMD method is predicted as the method of the future. Strategies using FFPC techniques are suggested in the form of a flow chart.

Applicability of EmporeTMTLC Sheets for Forced-Flow Planar Chromatography. I. Characterization of the Silica Sheets

Abstract Empore™ TLC silica sheets—a new separation medium for planar chromatography—are prepared from silica which is entrapped in an inert matrix of polytetrafluoroethylene (PTFE) microfibrils. It was established earlier that the separation power is only about 60% of that of conventional TLC. This was attributed to the very slow solvent migration velocity resulting from capillary action. In this paper the characteristics and applicability of EmporeTM TLC silica sheets are reported for the various forced-flow planar chromatographic (FFPC) techniques, such as overpressured layer chromatography (OPLC) and rotation planar chromatography (RPC). The preparation of the sheets and the relationship between the solvent front migration distance and migration time are given. The influence of the linear flow rate on the theoretical plate height and the relationship between the resolution and the linear flow rate are determined. Also, the influence of the development mode and solvent system on the densitometric evaluation is discussed. The influence of external force (overpressure or centrifugal force) on the structure of EmporeTM TLC silica sheets is demonstrated with the aid of scanning electron micrographs. The experiments show that Empore™ TLC silica sheets allow extremely rapid separations (5–20 min) by FFPC methods in all development modes. Good resolution is obtained because FFPC techniques are able to ensure the suitable mobile phase migration.