Modern TLC (Part 1 of 2)
Is Thin Layer Chromatography still up to date?
The principle of Thin Layer Chromatography (TLC) was described more than 100 years ago . For this method a relatively rigid support is coated with a thin layer of adsorbent. Suitable supports are glass plates, polyester or aluminum sheets. The substance mixture is separated in the adsorbent layer by elution with a suitable eluent. The real break-through as an analytical method came in the 1960s as a consequence of the pioneering work of E. Stahl .
Today TLC is a widely used technique in routine analyses. Already during training as lab assistant or during studies in natural science young scientist may have contact with this chromatographic procedure, either with introductory kits for scientific education (TLC micro-sets) or during qualitative analyses of organic syntheses with TLC sheets such as ALUGRAM® Xtra SIL G, 4 x 8 cm.
Due to its convenient and economical handling this method is very often used in scientific laboratories.
TLC is a frequently used analytical tool in:
- Clinical diagnostics,
- Natural Products
- Food, and
- Many other domains
Although the method is very well known, the scope of efficient application is frequently not recognized. For this reason, we wish to present below some powerful techniques and up-to-date products.
State-of-the-art TLC silica layers
Harder Plate Surfaces
Often TLC plates or sheets are labeled with a lead pencil prior to application of the sample and the analytical result is marked by outlining the substance spot. However, conventional silica layers may be damaged by this procedure, rendering the plate useless. Due to the improved binder system ADAMANT glass plates exhibit excellent hardness of the layer, allowing labeling of the plates without any difficulty.
Narrow Optimized Particle Size Distribution
Optimized particle size distribution results in an increased separation efficiency, a beneficial feature, e.g., for the separation of pharmaceuticals like analgesics.
Improved UV Indicators
A UV indicator with increased brilliance combined with a low-noise background allows application of the plates for trace analyses.
Instrumental TLC and Automation
Especially when used in instrumental Thin Layer Chromatography (also called Planar Chromatography ), these properties can increase the analytical efficiency. Automation of the steps sample application, chromatographic separation, derivatization with visualization reagents (if necessary), photometric direct evaluation and archiving allows to increase the sample throughput in quantitative analyses. Due to further advantages instrumental TLC can compete with HPLC as quantitative method. Often the efforts for sample preparation are lower. Irreversible damage caused by matrix constituents, which may destroy an HPLC column, is irrelevant for TLC plates, since they are disposed of after one-time application. In addition, there are no restrictions for the choice of solvents due to their inherent adsorption. Unlike in HPLC the solvent is evaporated prior to detection (in UV light).
Instrumental Planar Chromatography with ADAMANT glass plates is often used for:
- identity establishment,
- purity assays,
- quantitative analyses, and
- stability studies.
Inexpensive Aluminum Sheets for Adsorbent Support
Cost-saving application of aluminum sheets, especially appreciated in universities, has also been optimized in recent years. Thus, ALUGRAM® Xtra SIL G allows easy and reliable cutting without flaking of silica, due to an improved binder system. Use of aluminum sheets does not mean to forgo excellent separation efficiency as the separation of nutmeg ingredients shows.
Application of large volumes of very dilute samples can cause irregular spreading of substance spots, which makes evaluation difficult. To solve this problem, silica-coated glass plates with a concentrating zone of the inactive adsorbent kieselguhr are known for decades. Of late this layer is also available as aluminum sheet. The following figure shows concentration of a sample on an ALUGRAM® Xtra SILGUR
Concentration of samples