Optimize Each Step of Solid-Phase Extraction
Every step of solid-phase extraction can be performed rapidly and reliably using the LiChrolut® extraction unit from Merck. This transparent, vacuum-suitable unit made of glass can be used to prepare up to 12 samples simultaneously.
Each step should be optimized to ensure maximum recovery.
1. Conditioning the Sorbent
In the case of chemically modified silica gels, solvation with an organic solvent (acetonitrile or methanol) is necessary prior to conditioning i.e. preparation of sorbent for sample milieu with water or buffer solution in order to be accessible for the analyte. This is a prerequisite for reproducible sorption of the analyte. Excess organic solvent is removed using water or a buffer solution.
2. Application of the Sample
The sample solution is forced by vacuum or pressure through the conditioned extraction cartridge. In this process, the analyte concentrates itself as a narrow zone on the sorbent. Ideally, no matrix components will be adsorbed or run through the extraction cartridge.
Other interfering matrix components are removed from the surface of the stationary phase with a small volume of water or buffer. A water-buffer mixture containing a small quantity of methanol can also be used.
4. Elution of Adsorbed Analytes
In the final step of solid-phase extraction, the analyte is desorbed with a suitable solvent and eluted. After concentration or dilution of the eluate, analysis can follow immediately. A solvent should be selected that weakens the reaction between analyte and sorbent, and facilitates the distribution of the analyte throughout the eluent. The choice of solvent should be based on extensive knowledge about the analyte’s structure, solubility, polarity and lipophilic properties (distribution coefficients).