Procedure

A typical procedure for running a microcolumn under positive pressure is outlined below:

1. Take a Pasteur pipette and insert a small ball of cotton wool into the neck of the pipette, in the same way as used for pipette filtration. Be careful not to overly compress the cotton wool as this can slow the elution of solvent later.

2. Load the pipette with the desired packing material, to the desired depth. This can be achieved either with a small funnel (eg a piece of filter paper folded to allow a solid to be poured into the pipette), or the pipette can be used to directly scoop the packing material up into the pipette.

3. Clamp the pipette over a collection flask (a small conical flask, volumetric or sample vial are commonly used).

4. Optionally, pre-solvate the packing material with the elution solvent using an additional Pasteur pipette.

5. Add a solution of the material to be purified via Pasteur pipette. There are a number of options to elute the compound through the microcolumn:

• Allow the material to run through slowly by gravity.

• Use a pipette teat to help elute the material. Slide the teat carefully onto the microcolumn and gently squeeze the teat to allow the solvent to elute. When the teat has been fully compressed, without reducing the squeeze on the teat, gently slide it off the microcolumn, then allow it to reinflate. If it is allowed to reinflate whilst on the microcolumn it may disturb the packing material as air is drawn through the length of the column.

• Use a gentle flow of a compressed gas (eg air or nitrogen) to force the liquid through. This method requires practice to avoid losing material by splashing it out of the microcolumn and can also evaporate the solvent, which may be more of a problem in solvent mixtures.

6. Continue running the column until you are satisfied that all the desired material has eluted. There is a relationship between the quantity of solvent required, the amount of packing material and the retention of the compound(s) of interest (eg Rf).

7. The collection flask may be used directly, diluted, concentrated, allowed to crystallise or used in subsequent workup steps as required.

Example setup