Pigment chromatography separates different colored pigments based on their solubility and how they interact with a stationary phase (like paper) and a mobile phase (a solvent).
The Process Explained
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Sample Application: A small spot of the pigment mixture (e.g., plant extract) is applied to a chromatography paper.
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Solvent Development: The bottom edge of the paper is placed in a solvent. The solvent travels up the paper via capillary action.
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Pigment Separation: As the solvent moves, it carries the different pigments with it. However, pigments travel at different rates because of their varying solubilities in the solvent. More soluble pigments travel farther, while less soluble pigments remain closer to the starting point. This separation creates distinct bands of color.
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Visualization: The separated pigments are now visible as distinct bands on the paper. The different colors represent different pigments.
The reference material states: "In paper chromatography, paper marked with an unknown, such as plant extract, is placed in a developing chamber with a specified solvent. The solvent carries the dissolved pigments as it moves up the paper. The pigments are carried at different rates because they are not equally soluble." This accurately describes the core principle of pigment separation through differing solubilities and subsequent movement rates within the solvent.
Example: Plant Pigments
Imagine separating the pigments in a leaf extract. Chlorophyll (green), carotenoids (yellow/orange), and xanthophylls (yellow) will separate into distinct bands. Chlorophyll, being less soluble in the chosen solvent, might stay lower on the paper, while the more soluble carotenoids travel further.
Practical Applications
Pigment chromatography is used in various fields, including:
- Biology: Identifying pigments in plants and other organisms.
- Chemistry: Separating and analyzing mixtures of dyes and other colored compounds.
- Forensic science: Analyzing inks and dyes in documents.
