Why Is It Necessary to Dry the SPE Sorbent Before Elution?

Sample Preparation Tip

Level: Intermediate

Solid Phase Extraction (SPE) is one of the most highly selective sample preparation methods, meaning that the targeted analytes and their matrices must be considered when choosing the correct SPE sorbent and format. Drying down the sorbent before elution is an important step.

Wash solvents are used to flush out unwanted compounds (i.e., contaminants). If the wash solvent is not completely removed, then residual wash solvent could contaminate the final elution.
If you do not dry the SPE sufficiently, it could make the final solution less concentrated and result in a reduction in sensitivity.
Drying helps physically break down the interactions between the sorbent and analyte for a more concentrated extract.

After the wash solvent has been passed through the cartridge, continue to apply negative pressure (vacuum) or positive pressure. Use this pressure to dry the cartridge for 2 to 5 minutes (or until dry). Turn off the pressure and wipe the tips of the manifold needles to remove any residual solvent.

Notes

Reproducibility: Drying removes traces of residual sample/matrix and wash solvent from the sorbent. This produces a more concentrated final extract with a consistent volume and composition and yields better reproducibility and higher recoveries.
Immiscibility: Drying is especially critical when using elution solvents that are immiscible with water (e.g. hexane, ethyl acetate, and methylene chloride). Residual water in the sorbent bed may prevent dissolution of the analyte in the elution solvent, resulting in low recoveries and irreproducibility.
Over-drying: Avoid over-drying the sorbent, since in some cases, analyte recovery may decrease with excessive vacuum or drying times above 5 minutes. Dry cartridges look distinctly different from moist ones. Make a note of the cartridge appearance before and after conditioning. Also, you could touch the cartridge while it is drying; wet cartridges feel colder than dry cartridges.