Butanol is not typically used directly in paper chromatography as a mobile phase. It's usually used in combination with other solvents to create a suitable mobile phase for separating different components in a mixture.

Here's how butanol is typically used in paper chromatography:

1. As a component of a mixed solvent system: Butanol is often used in conjunction with other solvents like water and acetic acid. This creates a mixed solvent system that provides the optimal balance of polarity for separating components based on their differing polarities.

2. Increasing the polarity of the mobile phase: Butanol is less polar than water and more polar than other alcohols like methanol or ethanol. By adjusting the ratio of butanol to water and other solvents, you can fine-tune the polarity of the mobile phase to achieve better separation of the components.

3. Improving resolution: By carefully selecting the right butanol concentration, you can improve the separation of compounds with similar polarities, leading to better resolution.

Examples of mixed solvent systems with butanol:

* Butanol:Acetic Acid:Water (BAW): A common system used for separating amino acids. The specific ratio of the three components can be adjusted to achieve the desired separation.

* Butanol:Ethanol:Water (BEW): Another popular system used for separating pigments, dyes, and other compounds.

In summary: Butanol's function in paper chromatography is to act as a component of a mixed solvent system that is used as the mobile phase. By adjusting the ratio of butanol to other solvents, you can optimize the polarity of the mobile phase and achieve better separation of the components based on their differences in polarity.