Solid Phase Extraction (SPE)
Solid Phase Extraction (SPE) is an advanced and efficient technique used for rapid, selective sample preparation and purification before chromatographic analysis, including methods such as High-Performance Liquid Chromatography (HPLC), Gas Chromatography (GC), or Thin-Layer Chromatography (TLC). This technique involves isolating one or more target analytes from a liquid sample by utilizing a solid stationary phase, where the compounds are extracted, partitioned, and/or adsorbed. By selectively capturing the analytes of interest while removing interfering substances, SPE enhances the sensitivity, accuracy, and reproducibility of subsequent chromatographic procedures, ensuring a cleaner, more concentrated sample for detailed analysis.
Overview
Benefits of Solid Phase Extraction
Sample preparation using SPE simplifies the original matrix, making the sample more suitable for further analytical procedures. This results in improved qualitative and quantitative analysis. Additionally, a simplified matrix reduces the strain on the analytical system, which can help extend the system's lifespan. Some key benefits of an optimal SPE procedure include:
- Converting sample matrices to be more compatible with target chromatographic methods
- Concentrating analytes for improved sensitivity (trace enrichment)
- Removing interfering substances that cause background noise or poor sensitivity
- Protecting the analytical column from contaminants
- Automating the extraction process
How Does Solid Phase Extraction Work?
SPE works by using a stationary phase (sorbent or resin) to bind either the analyte or unwanted impurities through strong but reversible interactions. This allows the analyte of interest to be isolated from the complex sample matrix. SPE is a selective and versatile technique, as various sorbents and elution conditions are available, making it adaptable to different analytes and sample types.
Common SPE Sorbents
SPE employs various sorbents for different types of samples and analytes. Some of the most common sorbents include:
- Silica-based sorbents: Reversed-phase (C18, C8, cyano, phenyl), Normal phase (silica, diol, NH2), Ion exchange (SAX, WCX, SCX)
- Carbon-based sorbents
- Polymer-based sorbents: Available in various compositions and functionalities
- Other sorbents: Florisil® (magnesium silicate) or Alumina
- Mixed-bed sorbents: Combinations of different sorbents in sequential layers
SPE Strategies
Two common strategies for SPE include:
- Bind-Elute SPE: In this method, the analyte of interest binds to the sorbent while matrix interferences pass through. Afterward, the analyte is eluted using a suitable solvent.
- Interference Removal SPE: Here, matrix interferences are captured on the sorbent while the analytes of interest pass through. HybridSPE and QuEChERS are examples of methods based on interference removal.
Selecting the Optimal SPE Method
The optimal SPE method depends on the analyte's properties, such as its structure, solubility, polarity, and lipophilicity. Selection guides can help identify the most appropriate stationary phase and solvent based on the specific application.
Common Applications of Solid Phase Extraction
SPE is widely used in several industries for various types of analysis, including:
- Pharmaceuticals: Analysis of pharmaceutical compounds and metabolites in biological fluids
- Forensic: Detection of drugs of abuse in biological fluids
- Environmental: Identification of pollutants in drinking and wastewater
- Food and Agrochemical: Pesticides, antibiotics, and mycotoxins in food or agricultural matrices
- Biochemistry: Desalting of proteins and peptides, fractionation of lipids
- Nutritional: Analysis of water- and fat-soluble vitamins