What is chromatography? Describe, with the aid of a diagram, how you would separate the indicators in a mixture of indicators using paper chromatography, thin-layer chromatography or column chromatography - Leaving Cert Chemistry - Question b - 2007

1. Medium: In paper chromatography, the stationary phase is a sheet of absorbent paper, while the mobile phase is a solvent (usually a mixture). In thin-layer chromatography (TLC), the stationary phase is a thin layer of adsorbent material on a glass or plastic plate, and the mobile phase is also a solvent. For column chromatography, the stationary phase is packed in a vertical column, with the mobile phase flowing through it.

2. Application of Sample: A small spot of the indicator mixture is placed on the stationary phase (paper or plate) for paper/TLC or on top of the column for column chromatography.

3. Elution (Development): The mobile phase is allowed to move through the stationary phase. In paper or TLC, the solvent carries the components of the mixture up the paper or plate by capillary action. In column chromatography, the mobile phase flushes the different components down the column.

4. Separation: As the components move at different rates due to their varying affinities to the stationary phase, distinct bands of color will appear on the paper or plate when using paper or TLC. For column chromatography, different fractions of the eluate will be collected at the bottom of the column, each containing different components.

The type of chromatography commonly used for the separation of dyes taken from fibres in forensic work is thin-layer chromatography (TLC).