Sample Preparation Technical Tip
Level: Basic
I am getting a low recovery from my SPE method, how do I fix the problem?
If you are working with a known, good method, we would recommend that you:
• Check all solutions used for the SPE method to ensure that nothing has been mislabelled etc.
• Consider the process, was flow potentially too fast during loading or elution? Could the cartridges have been allowed to dry between equilibration and sample loading?
It is generally quickest to simply repeat the extraction, taking care of these points.
If however you are developing a new method, it will be necessary to “track down” your analyte. The first thing we would recommend is to make up a solution of the analyte without sample matrix (to use as an ideal sample). Then work through the sample method:
• Condition the cartridge
• Equilibrate the cartridge
• Load the sample, collecting the flow through. Analyse this for analyte content. If analyte is found in this fraction it would suggest:
○ Sample solvent is too strong, or the pH is incorrect
○ Loading flow rate is too high
○ You have breakthrough because either sample load is too high, or sorbent mass is too low.
If analyte is not found in the load fraction, proceed to the wash step.
• Wash the cartridge, retaining the wash fraction. Again, analyse for analyte content. If analyte is found in the wash fraction this suggests:
○ Wash solvent is too strong
○ Wash solvent is not at the correct pH
• If the analyte has not been found in the load or wash fractions then the analyte must be retained on the cartridge.
○ Try using a stronger elution solvent
○ Ensure pH of the elution solvent is correct
○ If the first 2 suggestions don’t help, try using a less retentive sorbent (in reversed phase, try switching a C18 cartridge for a C8 if the analytes are very hydrophobic).
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