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How do I prepare column chromatography?
Posted May 8, 2024
Answer
- Column Preparation: Plug a Pasteur pipet with a tiny amount of cotton. Add dry silica gel adsorbent to the column (230-400 mesh), packing it down lightly. Ensure the silica gel fills the column just below the indent on the pipet. Securely clamp the filled column to a ring stand.
- Pre-elute the Column: Add hexanes (or specified solvent) to the top of the silica gel. Observe the solvent flow and level, ensuring it does not drop below the top of the silica. The process can be sped up using a pipet bulb to force solvent through the silica gel.
- Load the Sample onto the Column: Use either the wet or dry method to load the sample onto the column. For the wet method, dissolve the sample in a small amount of solvent and load it onto the column. For the dry method, dissolve the sample in the minimum amount of solvent, add silica gel, swirl until dry, then transfer to the column.
- Elute the Column: Force solvent through the column, pressing on the top of the Pasteur pipet with a pipet bulb. Add fresh solvent as necessary to prevent the silica from going dry. Collect fractions as the compound(s) elute, changing the collection beaker when needed.
- (Optional) Elute with Second Solvent: If separating multiple compounds, change the eluting solvent to a more polar system as determined by TLC. Continue elution as in step 4.
- Analyze the Fractions: Combine like-colored fractions if colored, or analyze by TLC if not colored. Once the composition of each fraction is known, combine fractions containing the desired compound(s).
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