Instant Notes: Analytical Chemistry

Section D – Separation techniques

D3 THIN-LAYER

CHROMATOGRAPHY

Thin-layer chromatographyis a form of planar chromatography similar to

paper chromatography, but the stationary phase is a finely-divided sorbent

spread as a thin layer on a supporting flat plastic, aluminum or glass plate.

Solutes migrate through the stationary phase at rates determined by their distri-

bution ratios(Topic D2), those with the largest values moving the least, if at all,

whilst those with the smallest values moving with the advancing mobile phase,

or solvent front. A typical TLCprocedure consists of the following steps:

● sufficient mobile phase to provide about a 0.5 cm depth of liquid is poured

into a development tank,or chamber, which is then covered and allowed to

Principles and
procedures

Key Notes

Thin-layer chromatography is a technique where the components of

mixtures separate by differential migration through a planar bed of a

stationary phase, the mobile phase flowing by virtue of capillary forces.

The solutes are detected in situon the surface of the thin-layer plate by

visualizing reagents after the chromatography has been completed.

A variety of finely-divided particulate sorbents are used as thin-layer

stationary phases. These include silica-gel, cellulose powder, ion-

exchange resins, restricted pore-size materials, and chiral selectors.

Single solvents or blends of two or more solvents having the appropriate

overall polarity necessary to achieve the required separation are used as

mobile phases. They range from nonpolar hydrocarbons to polar

alcohols, water, and acidic or basic solvents.

Methods of visualizing solutes include spraying the surface of the thin-

layer plate with a chromogenic reagent, or viewing it under a UV lamp if

the sorbent has been treated with a fluorescent indicator.

Alternative development procedures aimed at improving

chromatographic performance have been introduced, and new stationary

phases are becoming available.

Thin-layer chromatography is used primarily as a qualitative analytical

technique for the identification of organic and inorganic solutes by

comparisons of samples with standards chromatographed

simultaneously. Quantitative analysis is possible but precision is

relatively poor.

Related topic Principles of chromatography (D2)

Principles and

procedures

Stationary phase

Mobile phase

Solute detection

Alternative TLC

procedures

Applications of TLC