SPE Elution Mode and Operation Steps

SPE (Solid Phase Extraction) is a sample pretreatment technique developed in the late 1870s. At present, it is used in environmental analysis, biological sample analysis, and food analysis.

SPE can be used with all samples (liquids, solids, creams, gaseous, and so on), but liquid samples are the easiest to handle.

Elution mode of SPE

There are two primary elution modes in SPE:

  1. Isocratic Elution: In this mode, a single solvent or a solvent mixture with a constant composition is used to elute the analytes from the SPE column. Isocratic elution is simple and quick but might not provide the desired selectivity for complex samples. A solvent with a stronger affinity for the target compound was used for elution: the target compound had a stronger affinity than the distractor with the adsorbent.
  2. Gradient Elution: Gradient elution involves using a solvent mixture with a changing composition to gradually elute the analytes from the SPE column. This method provides better selectivity and resolution for complex samples and is often used for challenging separations. Direct elution of the target compound: the affinity between the target compound and the adsorbent is stronger than that of the distractor.

Operation steps of SPE

  1. Pretreatment of extraction column: i. Wetting and activation SPE fillers; ii. To remove possible impurities from the filler.
  2. Conditioning: Before sample loading, condition the SPE column to prepare the stationary phase for analyte retention. The conditioning solvent is usually the same solvent used in the sample loading step but without the analytes of interest.
  3. Sample Loading: Load the sample onto the conditioned SPE column. The sample is usually dissolved in a compatible solvent to facilitate its interaction with the stationary phase. The target analytes will selectively adsorb onto the solid phase while unwanted matrix components are washed away. i. Compression; ii. Vacuum extraction; iii. Centrifugal
  4. Washing: To remove any interfering substances that may have been retained on the column during sample loading, perform a washing step using a solvent or solvent mixture that is selective in removing these interferences while retaining the analytes of interest on the column.
  5. Elution: This is the key step for obtaining the analytes of interest. Use an elution solvent or solvent mixture that disrupts the analyte-stationary phase interactions, allowing the analytes to be released from the SPE column. The elution solvent’s strength and composition can be adjusted based on the analyte’s affinity for the stationary phase. In order to remove the small amount of matrix interference components adsorbed on the SPE cartridges.
  6. Collecting the Eluate: As the elution solvent passes through the SPE column, it carries the eluted analytes out. Collect the eluate in a clean vial or collection tube.
  7. Evaporation/Concentration: Depending on the analysis method, the eluate may require further concentration or solvent exchange before analysis. Techniques like nitrogen blow-down, solvent evaporation, or solvent exchange may be used for this purpose.
  8. Final Analysis: Analyze the concentrated eluate using the appropriate analytical technique, such as HPLC, GC, or LC-MS, to quantify and identify the target analytes.

Select the appropriate eluting solvent to eluate the analyte, collect the eluent, and dry the solvent for later use.

The basic device of SPE: SPE cartridges; solid-phase extraction filter.