Solid Phase Extraction (SPE)

Solid phase extraction (SPE) is a technique designed for rapid, selective sample preparation and purification prior to the chromatographic analysis (e.g. HPLC, GC, TLC). In SPE, one or more analytes from a liquid sample are isolated by extracting, partitioning, and/or adsorbing onto a solid stationary phase.  

Sample preparation by SPE changes the original matrix of a sample to a simpler matrix environment. This renders the sample more suitable for subsequent analytical chromatography, often simplifying and improving the final qualitative and quantitative analysis. The simpler sample matrix also lessons the demand placed on an analytical system, potentially extending the system’s lifetime.

An optimal SPE procedure can allow you to:

• Switch sample matrices to be more compatible with the target chromatographic method.
• Concentrate analytes (trace enrichment) for increased sensitivity.
• Remove interferences that cause high background, misleading peaks, and/or poor sensitivity during chromatographic analysis.
• Protect the analytical column from contaminants.
• Automate the extraction process.

How does SPE work?

In SPE, the stationary phase (a sorbent or resin) binds either the analyte or impurity through strong but reversible interactions to reliably and rapidly extract the analyte of interest from a complex sample.

SPE is selective and versatile as many different sorbents and elution conditions are available for different analytes and matrices. Common SPE sorbents include:

• Silica-based
  • Reversed phase (C18, C8, cyano, phenyl)
  • Normal phase (silica, diol, NH₂)
  • Ion exchange (SAX, WCX, SCX)
• Carbon-based
• Polymer-based (various compositions, different functionalities)
• Others, for example Florisil^® (magnesium silicate) or Alumina
• Mixed-bed: Combinations of nearly any of the above in sequential layers

Strategies for SPE

In ‘Bind‒Elute SPE’, the analyte of interest is captured by the sorbent and the matrix interferences pass through the cartridge. In ‘Interference Removal SPE’, the matrix interferences are captured on the sorbent and the analytes of interest pass through. Both HybridSPE and QuEChERS SPE methods work via Interference Removal.

The optimal SPE method depends on the analyte’s structure, solubility, polarity and lipophilic properties (distribution coefficients). Selection guides are available to help choose the most favorable stationary phase and solvent for the application of interest.

Common applications of SPE

SPE is frequently used in the pharmaceutical, clinical and high-throughput diagnostic testing, forensic, environmental, and food/agrochemical industries for analyses related to:

• Pharmaceutical compounds and metabolites in biological fluids
• Drugs of abuse in biological fluids
• Environmental pollutants in drinking and wastewater
• Pesticides, antibiotics or mycotoxins in food/agricultural matrices
• Desalting of proteins and peptides
• Fractionation of lipids
• Water- and fat-soluble vitamins