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It isn’t easy and lengthy to remove solid phase substances. In this post, we’ve collected 10 tips to simplify the process. From drying to cleaning, these suggestions will help you make the most of your extraction efforts. What are you waiting for to do? Get started extracting solid phase materials now!

1. Fresh standards are best

Certain analytes are unstable if stored for extended durations and could be precipitated from solution. This can affect the recovery value and calibration standards of a test. The procedure must be started with the latest standards.

2. Optimise loading pH

The pH of any SPE technique can have a significant impact on the retention rate of compounds and can be used to boost retention. The reversed phase method is a method to regulate the pH of the solution and neutralize any charge in an analyte.

This will enhance interactions with the resin and make the analyte more hydrophobic. For the basic compounds, set 2 pH ABOVE pKa and for acidic compounds, set 2 pH units BELOW pKa.

3. Be aware of your compound

The properties of the compounds being analyzed can have a huge effect on the type of SPE that is carried out. The two most significant measurements are the pKa (half Ionized) and the log P (half un-ionized) of the analytes. pKa refers to the half-ionized value of an analyte. Log P measures the hydrophobicity a compound has.

4. Loose-packed vs. composited

Materials that are loose can cause problems within the sorbent beds like channeling, compression and emptying.

All of these variables could have an impact on the reproducibility and recovery of results from tests. This issue can be solved with composite products like the Microlute CP range. They are designed to improve reproducibility and recovery of SPE techniques.

5. Sorbent conditioning

When the pKa value for a sorbent has been determined, the sorbent can be activated and prepared to bind analytes by conditioning. The silica is bound by an functionalized moiety that is usually lying flat on the surface of particles in most silica-based SPE sorbents.

The conditioning step that is carried out using a water-miscible, organic solvent (e.g. MeOH), gives them the most surface area that analytes can connect to and bind because it causes the bonded functionalities to stand up’ above the rest.

If the sorbent you are using is not water-wettable, this procedure might not be required. However solvent washing can increase the cleanliness of extracts.

6. Refine wash and elution strength

Wash and elution strength can be adjusted to provide the cleanest extracts When using reversed or mixed phase SPE product. Log P is the most suitable property to aid in selecting these settings.

Low Log P – Lower the organic strength of the solvent for elution to avoid interference from hydrophobic substances while still eluting your analyte you prefer.

High Log P – Use stronger organic strength during the wash step.

7. Know your sorbent

To adjust the pH of solutions throughout the washing and loading steps, without the recourse to deionizing chemicals and resins (weak Ionic Resins, only) it is important to know and utilize the pKa values of analytes.

8. Follow QuEChERS (rates)

In order to achieve an efficient reversed phase SPE workflow the flow rate is crucial. Van der Waals interactions between the analytes and sorbents are crucial for the retention process.

In an SPE process high flow rates hamper the ability of the analyte in question to adhere to the sorbent medium properly and may cause an improvement in the load and wash procedures of an SPE. Slow and steady flow is the ideal. The goal should be to achieve a flow rate of one drop per second (1 milliliter/minute).

9. Dry the SPE resin prior it is used for elution.

Silica can collapse in its stationary phase when it is dry. Don’t allow silica-based resins to become dry in the last step of the SPE process. This is particularly important in the load step.

Recovery can be decreased by limiting the interaction between analytes and bonded phases and other substances. These guidelines are applicable to silica and polymeric resins.

The resin should be dried using vacuum or positive pressure after the washing steps have been completed. Use vacuum or positive pressure for at least 3 minutes, or until solvent is gone.

If the method requires a dry down and reconstitution, the dry downtime can be significantly reduced through drying the resin since water is a component of most wash solvents, which is far more difficult to evaporate than most organic solvents.

Drying the SPE resin after washing can result in the solution being less concentrated and a diminution in the sensitivity to injection.

10. Dry down to an optimal level

Make sure that the chosen dry down technique is sufficiently vigorous to disturb the surface of the solvent used for elution, but not enough to trigger the possibility of expulsion of the solution out of the wells since this can cause severe %RSD and variations in recovery. Because the level of solvent fluctuates when drying down, this could be quite challenging.