How Does SPE Extraction Work During the Whole Process?

Solid Phase Extraction (SPE) is a sample preparation technique used in analytical chemistry to separate and concentrate analytes from a complex sample matrix. The process involves several key steps:

  1. Selection of SPE Cartridge:
    • Choose a cartridge with a sorbent material that has specific affinity for the analytes of interest. Common sorbents include silica, reversed-phase C18, and polymer-based materials.
  2. Conditioning:
    • The SPE cartridge is first prepared by passing a solvent (often the same as the mobile phase in chromatography) through it. This removes any residual impurities and activates the sorbent.
  3. Sample Loading:
    • The sample, typically dissolved in a compatible solvent, is then loaded onto the SPE cartridge. The sorbent retains the analytes while allowing unwanted components to pass through.
  4. Washing:
    • A wash solvent is used to remove any remaining impurities or interferences that may have been retained on the sorbent. This step helps improve the purity of the analytes.
  5. Drying (Optional):
    • In some cases, it may be necessary to dry the sorbent bed to remove any residual water before elution. This step is particularly important if water may interfere with subsequent analyses.
  6. Elution:
    • The analytes of interest are then recovered from the sorbent bed using an elution solvent. The elution solvent is chosen based on its ability to desorb the analytes from the sorbent.
  7. Concentration (Optional):
    • If higher analyte concentrations are desired, the eluent can be evaporated to reduce volume and increase concentration.
  8. Reconstitution:
    • The eluted analytes are reconstituted in a suitable solvent for further analysis. This may be the same solvent used in the initial sample preparation or a different one, depending on the analytical method.

The key principle behind SPE extraction is selective retention and elution of analytes based on their affinity for the sorbent material. This allows for efficient and specific isolation of target compounds from complex sample matrices.

It’s important to note that the success of an SPE extraction depends on factors like proper sorbent selection, optimized conditions for conditioning, loading, washing, and elution, as well as adherence to manufacturer guidelines and good laboratory practices. Additionally, waste disposal practices should be followed for used SPE cartridges and solvents.

 

Activation, also known as solvation, add a suitable solvent to expand the functional groups on the adsorbent and remove possible interferences on the adsorbent.

Equilibrium, remove the activated solvent to create a suitable solvent environment for sampling. Usually, use the same solvent of the sample solution. But for the ion exchange SPE cartridges, use the contrary solvent to the sample solution.

Retention, when the sample solution passes through the adsorbent, and the force between the adsorbent and certain compounds exceeds the force between the latter and the solvent, the compounds are fixed by the adsorbent, thus called retention; washing, after sampling, some of the interfering substances are retained together with the target compound.

It is necessary to add a suitable solution to remove the interferences to the greatest extent without affecting the retention of the target compound. Usually, the sample solvent for washing does not affect the recovery rate.

Elution, the strong elution ability solvent passes through the adsorbent to interrupt the interaction between the adsorbent and the retained compound so that these compounds flow out from the adsorbent with the solvent. Usually, the elution solvent which can only elute the target compound is the best choice.