Ultrathin-Layer Chromatography (UTLC)

Ultrathin-layer chromatography (UTLC) differs from high-performance thin-layer chromatography (HPTLC) and from thin-layer chromatography (TLC) in two basis things: the layer thickness, and the migration distances of the analytes. UTLC has a monolithic or a nanostructured stationary silica gel phase bound directly to the glass plates. Layer thickness in UTLC is 10 μm, instead of 100–250 μm in HPTLC. Migration distances are in the range of 1–3 cm for UTLC, instead of 8–10 cm for HPTLC. Therefore, the major advantages of UTLC over HPTLC and TLC are the shorter development times and higher separation efficiency and sensitivity. Moreover, separations on UTLC plates require smaller reagent and sample volumes. However, the UTLC plates are very difficult to manage with the TLC and HPTLC equipment currently available. Therefore, the next challenge in this area is the development of an inexpensive solution with appropriate instrumentation (sensitive optical scanners and sample application systems). UTLC had been used for separations of many compounds, e.g., pharmaceutically active ingredients, pesticides, plasticisers, natural products, and other chemical substances.     

Contemporary Planar Chromatography

The review is devoted to the theory, instrumentation, and practical application of planar chromatography. The theoretical section is devoted to the separation mechanisms in planar chromatography and to the composition and properties of stationary phases. Attention is focused on quantitative planar chromatography, in particular, on the instrumental measurements of analytical signals and on the analysis of measurement errors.     

Two Dimensional Quantitative Analysis in Planar Chromatography

Abstract

The quantitative analysis of biological materials presents serious problems for the biochemist. The procedures to produce gels and separate phospholipids are time consuming and tedious. In the past, interpretation of the data was qualitative at best and guite subjective. With the introduction of sophisticated instrumentation and software, accurate and reliable data can be obtained.

In this paper, the methodology and techniques of two dimensional planar chromatography are explored. We will show that parameter selections can greatly influence the data. Comparisons of actual to calculated concentrations can show a 10% ? 55% variation depending on the sample, methodology and techniques used.     

UTLC of Flavonols in Sambucus nigra Flowers

JPC – Journal of Planar Chromatography – Modern TLC -     

Planar Chromatography of Free Industrial Amino Acids

JPC – Journal of Planar Chromatography – Modern TLC - Amino acids such as L-serine, L-threonine, L-phenylalanine, L-tryptophan, L-lysine, L-ornithine, L-arginine, L-valine, and...     

Principle and Potential of Gradient Elution in Planar Chromatography

It was the intention of this paper to show some recent developments in thin layer chroma-togrphy aiming at increasing the separation efficiency by instrumental means and techniquesusing existing separation layers. Gradient elution in the normal phase is a most efficient wayto achieve this goal. Multi-dimensional separations by coupling gradient elution column liquid chromatography inthe reversed phase with AMD gradient elution in normal phase is suitable to achieve newdimensions of separation numbers. Assuming that the N numbers reported for HPLC translateinto separation numbers near 100, by coupling the two kinds of chromatography, separationnumbers around 500 become practically usable.     

Capillary Electrokinetic Chromatography (CEC): An Introduction to a High-Efficiency Microanalytical Technique

Capillary electrokinetic chromatography (CEC, also called capillary electrochromatography) is a relatively new separation technique based on a combination of liquid chromatographic and electrophoretic separation methods. CEC offers both the efficiency of capillary electrophoresis (CE) and the selectivity and sample capacity of packed capillary high performance liquid chromatography (HPLC). These advantages are provided in part because of the favorable flow characteristics of electroosmosis, a method of pumping a liquid by applying a high potential axially to a thin, fluid-filled tube. The speed at which analytes move through the separation conduit under the influence of electroosmosis is quite uniform, regardless of the position of the analyte with respect to adjacent surfaces (within certain limits). This results in very little spreading of zones of analyte; narrow, compact bands of analytes are therefore maintained, which results in high efficiency. Because the capillaries used in CEC are packed with HPLC packing materials, the wealth of selectivities available in HPLC are also available in CEC. The high surface area of these packing materials enables CEC capillaries to accommodate relatively large amounts of sample, making detection a simpler task than it is in capillary electrophoresis (CE). This paper will briefly visit the theory and practice of CEC, and will provide examples of how CEC can be applied in sample analysis.     

Two-Dimensional Planar Chromatography with a Closed Adsorbent Layer

A new two-dimensional chromatography process on closed plates is proposed. A previously described device with ethanol as a mobile phase is used to experimentally study two-dimensional thin-layer chromatography (2D TLC) on plates with 5 × 5 and 10 × 10 cm sizes. This work includes the experimental study and comparison of the following TLC versions: (1) the proposed 2D TLC version with a closed adsorbent layer with 1D separation on closed plates (an ascending mobile phase flow) and (2) conventional 2D TLC with an open adsorbent layer. The ascending version of 2D TLC with a closed adsorbent layer considerably (byR~55%) shortens the chromatographic time, especially with the use of 5 × 5 cm plates in the 2D separation version compared with the 1D version on 10 × 10 cm plates.     

Variables that Affect Performance in Planar Chromatography with Electroosmotic Flow

JPC – Journal of Planar Chromatography – Modern TLC - Planar electrochromatography (PEC) is a mode of planar chromatography in which the mobile phase is driven by electroosmotic flow....     

Recycling Technique in Preparative Liquid Chromatography

Abstract

A theoretical and practical study of recycling technique is developped for preparative liquid chromatography. The optimal cycle number, n_opt, is determined for the separation of two solutes in such a way that the resolution between the second peak of cycle (n-1) and the first one of cycle n is equal to the resolution between the peaks of cycle n. A simple relationship is propounded to determine n_opt which only depends on retention volumes and external volume, but it does not depend on band spreading. With this recycling technique it is shown that the maximum injection volume under optimal recycling conditions is greater than n_opt times the maximum injection volume for one cycle. So the use of recycling can be opportune and beneficial to increase the throughput in preparative liquid chromatography.     

Hydrodynamic Chromatography: The Underutilized Size-Based Separation Technique

Chromatographia - Hydrodynamic chromatography (HDC) is a size-based liquid chromatographic technique with similar applications as size exclusion chromatography (SEC) and flow field flow...     

Reversed-Phase Pressurized Planar Electrochromatography and Planar Chromatography of Acetylsalicylic Acid,Caffeine, and Acetaminophen

JPC – Journal of Planar Chromatography – Modern TLC - We have investigated the use of pressurized planar electrochromatography (PPEC) and planar chromatography (TLC) for reversed-phase...     

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.     

Some Aspects of Chiral Separations in Planar Chromatography Compared with HPLC

JPC – Journal of Planar Chromatography – Modern TLC - The paper reviews the latest achievements in chiral separation by planar chromatography (PC) since 2001. The emphasis is on...     

An Estimation Technique of Molecular Weights of Bio-Oligomers by Reversed-Phase Liquid Chromatography

Abstract

A new simple and accurate method for molecular weight estimation of oligomers by reversed-phase liquid chromatography was developed and has been proposed to use in the investigation of bio-oligomers. Capacity factors (k′) of 24 peptides and proteins ranging in molecular weight from 200 to 70000 were measured independently under isocratic eluting conditions with slightly different acetonitrile contents in the mobile phase. Profiles of plots of the log k' values of the peptides and proteins against the acetonitrile contents were on straight lines with different slopes. These slopes were characteristic for each oligomer and found to be proportional to the two/thirds power of the molecular weight. This elution behavior of oligomers in reversed-phase liquid chromatography can be explained in terms of the solvophobic theory. The estimated molecular weights of several bio-oligomers were more accurate than those obtained by size-exclusion chromatography. when the range of molecular weights was limited from 10³ to 2×10⁴.     

Planar Chromatography of Some 1-Arylpiperazines Behaving as Dopaminergic Ligands

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of fourteen 1-arylpiperazine derivatives has been studied by thin-layer chromatography on both silica...