Solid-phase extraction

Solid-phase extraction (SPE) is a sample preparation method that is widely used in analytical chemistry to separate or concentrate analytes from a solution by adsorption onto a solid phase, followed by elution of the analyte with a solvent. SPE is a versatile technique that can be applied to a wide range of samples, including water, blood, urine, and food products. The method is particularly useful for isolating analytes from complex matrices and for pre-concentration of trace components.

Principles of Solid-Phase Extraction

The process of SPE involves passing a sample solution through a cartridge or disk containing a solid adsorbent. The adsorbent selectively retains the analytes of interest while allowing other components of the sample to pass through. The retained analytes are then eluted with a small volume of solvent that has a higher affinity for the analytes than the solid phase. The choice of adsorbent and elution solvent is critical and depends on the properties of the analytes and the matrix of the sample.

Types of Solid Phases

There are several types of solid phases used in SPE, each with different properties and applications:

• Silica-based adsorbents: These are the most commonly used adsorbents and include C18, C8, and phenyl phases. They are suitable for non-polar to moderately polar compounds.
• Polymer-based adsorbents: Such as styrene-divinylbenzene and methacrylate polymers, are used for a wide range of analytes, including polar compounds.
• Ion-exchange resins: These are used for charged analytes. Cation-exchange resins are used for positively charged analytes, while anion-exchange resins are used for negatively charged analytes.
• Affinity sorbents: These are used for selective extraction of specific analytes, such as antibodies or enzymes.

Applications

SPE is used in various fields, including environmental analysis, pharmaceutical analysis, food analysis, and clinical analysis. It is employed for the analysis of a wide range of analytes, including drugs, pesticides, hormones, and metabolites in complex matrices.

Procedure

The SPE procedure can be summarized in the following steps:

1. Conditioning of the SPE cartridge or disk with a solvent to activate the adsorbent.
2. Loading of the sample onto the cartridge or disk.
3. Washing the cartridge or disk to remove any matrix components or undesired analytes.
4. Elution of the analytes with an appropriate solvent.

Advantages and Limitations

The main advantages of SPE are its ability to concentrate trace analytes and to remove interfering substances from the sample matrix. It is a relatively quick and simple method that can be automated. However, SPE also has some limitations, including the cost of cartridges and the potential for analyte loss or degradation during the extraction process.

See Also

• Chromatography
• Liquid-liquid extraction
• Sample preparation (analytical chemistry)