Category: Methods of Purification and Separation

Pen ink consists of a mixture of dyes that can dissolve in the solvent and contaminate the chromatogram.

Pencil lead is usually made of insoluble graphite, which made it suitable for drawing the start line in paper chromatography.

The start line above the solvent level allows the solvent to move past the start line, carrying the dissolved samples along with it.

With the start line below the solvent level, the samples on the start line will dissolve in the solvent right at the beginning, contaminating the whole solvent, causing the chromatogram to be inaccurate.

For substances used in preparing food and drugs, it is important to ensure that only permitted substances are being used.

If a substance is impure, and laced with some other substances, these unapproved impurities might not be safe for human consumption, and lead to undesirable effects on human health.

To determine the purity of a substance, test its melting point or boiling point.

If it melts or boils at a fixed temperature, it is a pure substance.

Another method is to carry out a chromatography of the substance.

If it separates out into only one spot on the chromatogram, it is a pure substance.

A small amount of concentrated sample is placed on the starting line of a chromatography paper. The chromatography paper is placed inside a beaker containing a solvent. The solvent level should be below the starting line.

As the solvent moves up the paper, it separates the sample into its respective components.

The chromatography paper is removed before the solvent reaches the edge of the other end of the paper.