Procedure

A typical procedure for running a solid phase extraction under positive pressure is outlined below:

1. Obtain a new SPE cartridge and clamp above a small beaker.

2. Connect a piece of tubing fitted with a hard plastic end to the nitrogen line. You will use the plastic part to form a seal with the SPE cartridge to push solvent through the SPE column.

3. Solvate the solid phase with a suitable solvent and turn on the nitrogen to give a very gentle flow through the tubing. Carefully bring the hard plastic part into contact with the top of the cartridge to form a seal and push the solvent through the SPE cartridge. Be careful not to use too high a pressure, as this may result in blowing the liquid out of the cartridge. You should see the solvent start to be pushed through the SPE cartridge and drops fall from the end into the beaker. Stop blowing nitrogen through as soon as the liquid level reaches the top of the solid phase (ie don’t let the solid phase dry out). You may need to add further portions of solvent to remove air bubbles etc. You should ensure there are no air bubbles/gaps in the solid phase. For some desired solvent mixtures, you may not be able to directly solvate the material with the desired mixture and have to pre-solvate with another solvent first. For example if you wanted a ethanol/water mixture, you might first solvate with ethanol, then solvate with the ethanol/water mixture.

4. Load the material to be purified onto the column and carefully blow onto the solid phase using the stream of nitrogen.

5. Wash the column to remove unretained material. The choice of a wash solvent can be difficult. The solvent needs to be able to elute unwanted materials from the cartridge whilst keeping the desired components retained on the packing material. The solvent is loaded and carefully blown through the cartridge eluting unwanted material into the beaker. There may be multiple wash steps.

6. Change the beaker under the column for a vessel to collect the desired compound(s). Load a volume of the elution solvent and pass this through the column with nitrogen in order to elute the desired compounds them from the stationary phase.