Instruction
Solid phase extraction (SPE) is a sample preparation technique which separates target substance from mixture effectively by affinity and partition of analyte in stationary phase (i.e. solid adsorbent) and mobile phase (i.e. liquid phase). It 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. SPE not only improves analyte recovery and procedure simplicity, but also lowers reagent consumption than liquid extraction (LLE), one of the oldest used extraction techniques.
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.
SPE is now widely used in laboratories of various industries for treatment of aqueous samples and extracts due to lots of benefits. Sample preparation by SPE changes the original matrix of a sample to a simpler matrix environment.
Methods
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
To improve the efficiency and quality of SPE analysis, the process enables acceleration with the aid of vacuum; moreover, the drop rate can be regulated by vacuum control to prevent incomplete reaction.
The mobile phase of SPE is mainly solvent, so a chemical resistant vacuum pump that coated or made of polytetrafluoroethylene (PTFE) should be best choice to reduce the pump corrosion by chemical vapors.
Applications
- Pharmaceutical industry, such as components extraction and research of metabolite.
- Environmental Analysis, such as extraction of metals in water.
- Food testing, such as pesticide and veterinary drug residues.
- 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.
