Table 4.15(a) Chromogenic reagents for visualizing thin-layer chromatograms
Reagent Applications
iodine vapour general organic, unsaturated compounds
phosphomolybdic acid general organic
fluorescein/bromine general organic
sulphuric acid general organic (TLC only)
ninhydrin or isotin amino acids
2,4-dinitrophenylhydrazine ketones and aldehydes
H 2 S water, diphenylcarbazide or metalsrubeanic acid metals
aniline phthalate sugars
antimony trichloride steroids, essential oils
chloroplatinic acid alkaloids
bromothymol blue lipidsTable 4.15(b) Stationary phases for thin-layer chromatography
Stationary phase Predominant sorption process Use
silica gel adsorption or partition general
modified silica gels adsorption or partition similar to bonded phase HPLC
alumina adsorption or partition general
cellulose powder partition inorganic, amino acids, nucleotides, food-
dyes
kieselguhr partition sugars
modified celluloses e.g. DEAE
and CMion-exchange nucleotides, phospholipidsSephadex gels exclusion macromoleculesStationary Phase
Nature and Function of Thin-layer Materials
Any of the materials used in column, ion-exchange and exclusion chromatography can be used for TLC
provided that they can be obtained in the form of a homogeneous powder of fine particle size (1– 50
μm). Coarse materials will not easily form a uniform thin layer which adheres to a glass plate or other
supporting sheet. A list of some of the more important stationary phases and their uses is given in Table
4.15(b). Pre-coated thin-layer plates are available commercially but are relatively expensive. Plates with
a wide variety of stationary phases can be prepared in the laboratory using a mechanical spreading
apparatus. This consists of a trough to hold a slurry of the stationary phase and a flat bed to support a
number of plates. By moving the trough across the plates, an even coating of slurry is deposited from
which the solvent can be evaporated by oven-drying.
Silica gel or silicic acid, has found the most widespread use in TLC. It