Chromatography: Principles, Methods
Chromatography is a powerful separation technique used to separate, identify, and purify components of a mixture. It exploits differences in how substances partition between a stationary phase (solid or liquid) and a mobile phase (liquid or gas). Components migrate at different rates, allowing separation. It is fundamental in chemistry, biology, forensics, environmental science, and pharmaceutical analysis.
Principle of Chromatography
The mixture is dissolved in the mobile phase, which carries it through the stationary phase. Each component has a different affinity for the two phases → different migration speeds → separation. The retention factor (Rf) is a key parameter:
Rf is characteristic for a given compound under fixed conditions. It helps in identification.
Types of Chromatography
📄 Paper Chromatography
Stationary phase: paper (cellulose). Mobile phase: solvent. Used for separating dyes, amino acids, simple mixtures.
🧪 Thin Layer Chromatography (TLC)
Stationary phase: silica gel or alumina coated on glass plate. Fast, high resolution, widely used in organic chemistry.
🔬 Column Chromatography
Stationary phase packed in a vertical column. Mobile phase flows through, fractions collected. Used for preparative separations.
💨 Gas Chromatography (GC)
Mobile phase: inert gas (He, N₂). Stationary phase: liquid coated on solid support. For volatile compounds.
💧 High Performance Liquid Chromatography (HPLC)
High pressure forces mobile phase through column. High resolution, quantitative analysis.
🧬 Ion Exchange Chromatography
Separates ions and polar molecules based on charge. Used in protein purification, water softening.
🎨 Continuous Paper Chromatography Simulation
🧪 Real-time Chromatogram Development
Watch the solvent front rise continuously. Different components move at different speeds based on their polarity and the chosen solvent.
💡 The solvent front moves upward. Each component has a fixed migration velocity relative to the front (Rf value). The simulation runs continuously until the front reaches the top. Press Reset to start over, Pause/Play to control.
Retention Factor (Rf) and Identification
After development, the distances are measured. Rf values between 0 and 1 indicate separation. Unknown compounds can be identified by comparing Rf with standards.
Applications of Chromatography
- Pharmaceuticals: Purity testing, drug analysis, metabolite detection.
- Forensics: Analysis of ink, dyes, drugs, and toxicological samples.
- Environmental: Monitoring pesticides, pollutants, water contaminants.
- Food industry: Quality control, preservatives, vitamin analysis.
- Biochemistry: Protein purification, DNA sequencing (HPLC, GC).
📝 Chromatography – Quiz
1. What is the stationary phase in paper chromatography?
2. The formula for retention factor (Rf) is:
3. Which type of chromatography uses an inert gas as mobile phase?
4. In TLC, if a compound travels 4.2 cm and solvent front travels 6.0 cm, Rf is:
5. Which technique is best for separating heat‑sensitive, non‑volatile compounds?
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