Overview
This lecture explains how to use thin-layer chromatography (TLC) to monitor organic chemistry reactions, focusing on setup, process, and analyzation of results.
TLC Basics
- Thin-layer chromatography (TLC) separates compounds using a mobile phase (solvent) and a stationary phase (solid).
- The stationary phase in TLC is usually a plate coated with polar silica gel.
TLC Procedure
- Spot a small amount of your sample onto the silica gel plate.
- Prepare the developing chamber with a small amount of mobile phase (solvent or solvent mixture) and a wet paper to saturate the atmosphere.
- Place the TLC plate upright in the chamber, ensuring the spot is above the solvent level.
- Close the chamber to prevent solvent evaporation.
- The solvent moves up the plate by capillary action, carrying compounds with it.
- Remove the plate before the solvent front reaches the top and mark its final position with a pencil.
Visualization and Interpretation
- Use a UV lamp to visualize spots, as many compounds are invisible otherwise.
- Each spot represents a different compound present in the sample.
- TLC is qualitative: it reveals the number of components and compares relative polarities.
Polarity and Compound Identification
- Silica gel is very polar; polar compounds travel less far (are more attracted to the stationary phase).
- Nonpolar compounds travel farther (are more attracted to the mobile phase).
- For example, naphthalene (nonpolar) moves farther than benzoic acid (polar) due to differing attractions.
Key Terms & Definitions
- Thin-layer chromatography (TLC) — A method to separate compounds using a stationary and a mobile phase on a flat plate.
- Stationary phase — The solid phase (silica gel) that remains fixed in place during chromatography.
- Mobile phase — The liquid solvent that moves up the plate and carries sample compounds.
- Capillary action — The process by which liquid moves through or along a solid due to adhesion and cohesion.
- Polarity — A measure of how evenly electrons are distributed in a molecule, affecting how it interacts with the stationary and mobile phases.
Action Items / Next Steps
- Practice setting up and running a TLC experiment in lab.
- Review the polarity of common organic compounds for TLC analysis.