The Steps of Solid-Phase Extraction

The general steps of solid-phase extraction (SPE) can be divided into five steps: activation, sample loading, washing, drying, and elution. However, in practical applications, these steps can be adjusted based on the sample requirements for the analysis method. For example, when using ion exchange principles for sample extraction, it is necessary to add a step to adjust the pH of the extraction system.

Pre-treatment and activation of the SPE cartridge:

Activate the SPE cartridge with an appropriate solution to expand the hydrocarbon chain, increase the surface area for interaction with the target analyte, remove impurities adsorbed on the cartridge that may affect the analysis, ensure good extraction reproducibility, and keep the pre-treated SPE cartridge moist before sample loading.

Sample loading onto the SPE cartridge:

Add the sample to the SPE cartridge and pass it through the cartridge using positive or negative pressure, controlling the flow rate of the sample. For biological samples, the flow rate is generally controlled at 1.5 ml/min. For extraction based on ion exchange, the sample flow rate through the SPE cartridge should be appropriately reduced to ensure sufficient time for the target analyte to interact fully with the ion exchange functional groups on the SPE cartridge packing.

Washing of the SPE cartridge:

Use an appropriate washing solvent to selectively wash away weakly adsorbed impurities while retaining the target analyte on the SPE cartridge. The choice of washing solvent depends on the final analysis method.

Drying of the SPE cartridge:

If the final washing solvent is a buffer solution or water-soluble organic solvent and the analysis method is reverse-phase HPLC, residual water on the SPE cartridge has minimal impact on the analysis. However, when the elution solvent is a non-aqueous organic solvent or the analysis method is GC or GC-MS, drying of the SPE cartridge becomes particularly important.

Elution of the target analyte:

When selecting the elution solvent, consider using a sufficiently strong elution solvent to elute as many target analytes as possible with minimal solvent usage. Also, ensure that the elution solvent is selective enough to elute only the target analyte while retaining strongly adsorbed impurities on the cartridge.