TLC is More Than Normal Phase by Robert Cotta

Published On: March 1st, 2021Categories: Thin Layer ChromatographyComments Off

Rethinking TLC Plates: More Than Normal Phase

Thin-layer chromatography (TLC) is one of the most common tools in chemistry because it is fast, affordable, and reliable. When paired with TLC Plates, it becomes a simple way to separate and identify compounds in a mixture. In the same way that HPLC and other chromatography methods work, TLC can be run with either normal- or reversed-phase adsorbents. These adsorbents include silica gel, alumina, bonded silica gel, and several others.

Normal vs. Reversed-Phase TLC Plates

In most cases, normal-phase TLC Plates use unbonded silica gel, while reversed-phase TLC Plates use silica gel bonded with a C18 chain. Both serve as good starting points for separations. However, they differ in how they move and elute compounds, which means the results can vary greatly.

Exploring Other Stationary Phases

Even so, chemists are not limited to just these two. In fact, several other stationary phases can improve separations or give better insights. For example, diol, NH₂, CN, C2, C18-50, C18-W, and C18-100 phases each provide a unique level of polarity. By choosing carefully, you can often achieve clearer separations and more useful data.

Why Many Chemists Stay with Normal Phase

Still, most chemists stick to normal-phase TLC Plates. Why does this happen? Usually, it is because labs keep them in stock, or because researchers copy the methods used by others. Over time, this has become the “standard way” of doing TLC, even when other options may deliver better results.

Why You Should Try Alternatives

That said, trying different TLC Plates can bring clear benefits. For instance, alternative phases may give sharper separations, different elution orders, or improved results when compounds interact poorly with silica gel or C18. Therefore, expanding beyond the default choice can lead to stronger and more reliable data.

Conclusion

In conclusion, TLC Plates remain an essential tool for separating and identifying compounds. However, relying only on normal-phase silica can hold you back. By exploring other stationary phases and considering the solubility and behavior of your compounds, you can improve both the speed and quality of your separations.

Sorbent Material	Chromatographic Principle	Typical Applications
Silica Gel for Normal Phase
Silica HD, Silica G, Slicia XG	Normal Phase	Most frequent application of all TLC layers.
Nano silica 60, impregnated with caffeine for PAH determination	Charge transfer complexes	For PAH analysis based on charge-transfer complexes
Cyano-modified layer CN	Moderately polar, normal and reversed-phase	Hydrophilic or charged samples, as well as steroids, hormones, phenols, and preservatives.
Diol-modified layer - OH	Moderately polar, normal and reversed-phase	Steroids, pesticides, and plant constituents, less sensitive than silica to the water environment.
Amino-modified layer NH₂	Moderately Polar, normal and reversed-phase	Use to separate hydrophilic or charged samples, Vitamins, sugars, steroids, purine derivatives, xanthine, phenols, nucleotides, and pesticides
Bonded Silica Gel for Reversed Phase
C2	Reversed-phase with up to 80% Water, and Normal phase	Polar and Nonpolar substances (lipids, aromatics), lower retention than C18 plates
C18-100, Silanized C18	Reversed-Phase with up to 20% Water	Polar Substances such as: alkaloids, amino acids, barbiturates, polycyclic aromatic hydrocarbons (PAH), drugs, peptides, flavonoids, phenols, indole derivatives, steroids.
C18-50, Silanized C18	Reversed-phase with up to 60% water	Polar Substances such as: alkaloids, amino acids, barbiturates, polycyclic aromatic hydrocarbons (PAH), drugs, peptides, flavonoids, phenols, indole derivatives, steroids.
C18-W, C18 Wettable	Normal and reversed-phase, much faster than silanized C18 counterparts	Polar and non polar substances such as: Aminophenols, barbiturates, preservatives, nucleobases, PAH, steroids, tetracyclines, phthalates