# What is the function of thin layer in thin layer chromatography?

I just learned about the thin layer chromatography, which I think is basically the same as the paper chromatography.

I am wondering what is the function of the thin layer? I mean, what's special about thin layer, compared to normal chromatography paper? What mechanism/principle/property makes the thin layer special?

• Thin layer chromatography uses a stationary phase which is alumina or silica. These phases are much more polar than paper. So they are more efficient than paper for detecting impurities in a given mixture. Nov 2, 2021 at 20:26
• In addition, to the above, TLC compares well to column chromatography as for the stationary phase is the same or at least similar. Column chromatography is a purification method of outmost importance in organic chemistry. Nov 2, 2021 at 20:51

If you recall Tswett's original discovery of chromatography, he used a calcium carbonate column to separate the chlorophyll pigments (or different types of chlorophylls). Now calcium carbonate is a very fine powder and the permeation of liquid through a powder is very slow, especially if the column is long. Pressure drop across a column scales as 1/($$d_p^2$$), where $$d_p^2$$ is the particle diameter.