- What are the main differences between thin layer chromatography (TLC) and column chromatography (CC)? 2. Are CC and TLC operations conducted concurrently? Explain. 3. Name a few packing materials used in packing columns in Column Chromatography operations. 4. Explain the role of eluting solvent(s) in column chromatography procedures. 5. When performing column chromatography, which of the following compounds would you expect to elute first: Ferrocene of acetylferrocene? Explain why.
The Correct Answer and Explanation is :
1. Differences between Thin Layer Chromatography (TLC) and Column Chromatography (CC):
- Principle:
- TLC is a type of chromatography where a stationary phase (usually a thin layer of silica gel or alumina) is spread on a flat surface like a glass plate. The sample is applied in a small spot, and the mobile phase moves up the plate by capillary action, allowing separation based on compound polarity and affinity for the stationary phase.
- CC involves packing a vertical column with a solid stationary phase (e.g., silica gel), and the sample is loaded on top. A solvent or mixture of solvents (mobile phase) is then passed through the column, carrying components of the mixture at different rates, which separates them.
- Scale:
- TLC is primarily used for qualitative analysis and is usually done on a small scale (microliters of sample).
- CC is designed for both qualitative and quantitative analysis and typically works on a larger scale, allowing isolation and purification of compounds.
- Time:
- TLC is much faster, often taking just a few minutes.
- CC takes longer, ranging from hours to days depending on the complexity of the separation.
2. Are CC and TLC Operations Conducted Concurrently?
No, Column Chromatography (CC) and Thin Layer Chromatography (TLC) are not typically conducted concurrently, but they are often complementary. TLC is usually employed before or during a column chromatography experiment to help determine the solvent system and monitor the progress of separation. TLC provides a quick and easy way to assess the sample’s components and to adjust conditions in the column before starting the main separation.
3. Packing Materials Used in Column Chromatography:
Some common packing materials include:
- Silica Gel (SiO₂): The most commonly used stationary phase in column chromatography due to its polarity.
- Alumina (Al₂O₃): Another commonly used polar material, often used when separation by different polarity is required.
- Sephadex: A gel filtration material for size exclusion chromatography.
- Cellulose or Polymeric Resins: These are used for specific separations depending on the chemical properties of the compounds.
4. Role of Eluting Solvent(s) in Column Chromatography:
The eluting solvent in column chromatography serves several roles:
- It acts as the mobile phase, carrying the sample mixture through the stationary phase.
- It helps to dissolve and transport the compounds from the column.
- The choice of solvent or solvent mixture controls the rate of migration of different components based on their affinity for the stationary phase and their solubility in the solvent. More polar solvents tend to elute more polar compounds, while less polar solvents elute non-polar compounds.
5. Which Compound Would Elute First: Ferrocene or Acetylferrocene?
Ferrocene would be expected to elute first in column chromatography.
Explanation:
Ferrocene is a non-polar compound, whereas acetylferrocene is polar due to the presence of the acetyl group (-COCH₃). In column chromatography, compounds with lower polarity tend to interact less with the polar stationary phase (like silica gel), meaning they travel through the column faster. The polar acetylferrocene would have a stronger interaction with the stationary phase, leading to a slower movement through the column compared to ferrocene. Therefore, ferrocene would be eluted first with a non-polar or less polar solvent, while acetylferrocene would require a more polar solvent for its elution.