Column Chromatography

Summary

In this video, Lisa Nichols demonstrates how to purify a mixture using column chromatography. She begins by explaining the process of preparing the column and packing it with silica gel using the slurry method. After ensuring the proper setup, she shows how to add the sample, rinse it, and use air pressure to accelerate the elution. The goal is to separate acetyl ferrocene from contaminants like ferrocene. By collecting fractions and observing the separation, Lisa guides viewers through the final steps of combining the desired compound and purifying it using a rotary evaporator.

Takeaways

• 😀 Ensure the mixture to be purified is analyzed with techniques like TLC (Thin Layer Chromatography) to identify contaminants and target compounds.
• 😀 Choose an appropriate solvent system for the column chromatography, ensuring that the compound of interest is well separated from impurities.
• 😀 Use a fume hood when handling silica gel or alumina, as they are fine powders that can pose a breathing hazard.
• 😀 Pack the column using the slurry method by mixing silica gel with the solvent and carefully transferring it into the column.
• 😀 Rinse the sides of the column immediately after adding the slurry to prevent the silica gel from drying and becoming difficult to remove.
• 😀 Eliminate air bubbles trapped in the packed column by gently jostling the column, ensuring proper packing and flow.
• 😀 Add a layer of sand at the top of the column to prevent disturbing the silica gel when adding solvents or samples.
• 😀 Add the sample carefully to the column to avoid disrupting the silica gel. Use a pipette for accurate control and avoid squeezing the bulb too forcefully.
• 😀 Collect fractions from the column during elution, ensuring that the solvent level stays above the sand layer to maintain proper separation.
• 😀 Use air pressure to accelerate the flow of the solvent through the column, speeding up the process while maintaining separation efficiency.
• 😀 After elution, combine the fractions containing the desired compound, and use a rotavap to remove the solvent and recover the purified compound.

Q & A

What is the purpose of using column chromatography in this experiment?

The purpose of using column chromatography is to purify a mixture of acetyl ferrocene contaminated with ferrocene. The goal is to separate the acetyl ferrocene from the ferrocene based on their different properties.

How do you know that the mixture is contaminated with ferrocene?

The contamination with ferrocene is determined through Thin Layer Chromatography (TLC). The TLC shows a distinct spot for ferrocene, indicating its presence in the mixture.

Why is it important to choose the right solvent system for column chromatography?

Choosing the right solvent system is crucial because it ensures the target compound (acetyl ferrocene in this case) has the appropriate RF value (around 0.3) and is sufficiently separated from other contaminants, such as ferrocene.

What is the significance of the silica gel in the column?

Silica gel serves as the stationary phase in the column. It interacts with the sample, helping to separate the components of the mixture based on their different affinities for the silica gel.

Why is the column packed in the fume hood?

The column is packed in the fume hood to avoid inhaling the fine particles of silica gel or alumina, which can be a health hazard.

What is the purpose of adding sand to the top of the column?

Sand is added to the top of the column to protect the horizontal level of the silica gel and prevent disturbance when liquids are added, ensuring the separation process is not disrupted.

Why is it important not to let the solvent level go below the sand layer?

It is important to keep the solvent level above the sand layer to prevent the silica gel from drying out, which could lead to poor separation and blockages in the column.

What role does air pressure play in the column chromatography process?

Air pressure is used to speed up the elution process by pushing the solvent through the column faster. This helps achieve a better separation of compounds.

How do you know when to combine the fractions collected during elution?

Fractions are combined based on the compound of interest. If the compound is colored, it can be identified visually. For colorless compounds, Thin Layer Chromatography (TLC) is used to determine which fractions contain the target compound.

What should you do with the used column after the chromatography process is complete?

After the chromatography process, the column should be drained using air pressure, dried completely, and the used silica gel should be disposed of properly in a waste jar.