Determining a solvent system

The composition of an effective solvent system for running TLC plate depends on the stationary phase being used and the properties of the components of interest. There are many different commecially available TLC plates with varying stationary phases and it is possible to make custom plates with other materials. Stationary phases are broadly categorised into normal or reversed phase.

Optimising TLC systems is usually crried out in order to work out a suitable solvent system for column chromatography. Where the same stationary phase is used for the plates and column, TLC is a useful tool for determining effective conditions.

Normal phase

The most commonly used stationary phase is unmodified silica which is a normal phase stationary phase material. The silica is polar and interact strongly with polar compounds, causing polar analytes to be retained on the plate. Changing the solvent system affects how strongly the compounds are retained. The less polar the solvent system, the greater the analytes are retained by the stationary phase resulting in a lower Rf values and vice-versa. Generally solvents of low polarity are used for normal phase, and a list of common solvents and mixtures are given below:

Reversed phase

Reversed phase chromatography retain non-polar compounds on the stationary phase and use polar mobile phases. The Rf value of compounds increases (compounds move further) as the solvent system becomes more non-polar. Water is usually used as the main solvent and is combined with other solvents: