Solvent and solid-phase extraction

Solvent and solid-phase extraction are two techniques for separating mixtures of substances, either by selective transfer between two immiscible liquid phases or between a liquid and a solid phase. 

Extraction efficiency is defined as the fraction or percentage of a substance that can be extracted in one or more steps. Selectivity is the degree to which a substance can be separated from others in a mixture. 

Procedures are based on the extraction of nonpolar, uncharged species from an aqueous solution into an immiscible organic solvent, or the extraction of polar or ionized species into an aqueous solution from an organic solvent. 

Sorbents are particulate materials such as silica, chemically-modified silica, alumina and organic resins that can interact with and retain substances from solutions. Retained substances can be subsequently released back into a suitable solvent under controlled conditions. 

Sample solutions are passed through the sorbent under conditions where either the analytefs) are retained and matrix components washed through or the reverse. Retained analytes are removed with an alternative solvent before completing the analysis. 

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A simple first strategy to recover residues for ELA is to try existing multiresidue methods, or to use solvents and solid-phase extraction media that have proven satisfactory in the first steps of more involved instrumental analyses. This approach makes the transition from instrumental methods to ELA easier for technical personnel, and it facilitates confirmatory instrumental analysis during method validation. The uncommon structure of avermectin antibiotics makes it very unlikely that the ELA would detect compounds other than an avermectin in multi-residue extracts, though this remains to be tested. The greater concerns are completeness of the extractions, efficiency and reproducibility of recoveries, and freedom from non-specific matrix effects and interference by solvents. 

SAMPLE PREPARATION SOLVENT AND SOLID-PHASE EXTRACTION... 

Santos-Montes, A. Gonzalo-Lumbreras, R. Gasco-Lopez, A.I. Izquierdo-Homillos, R. Solvent and solid-phase extraction of natural and synthetic corticoids in human urine. J.Chromatogr.B, 1994, 652, 83-89... 

As most of the product is secreted and is thus concentrated in the culture broth, the recovery process starts with filtration, usually with a rotary vacuum filter, followed by a cascade of solvent and solid-phase extraction steps. 

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