Solid-phase extraction solvent strength

Solid phase extraction (SPE) involves the separation of components of samples in solution through their selective interaction with and retention by a solid, particulate sorbent. SPE depends on differences in the affinities of the various components of the sample for the sorbent. The mechanisms of the interactions are virtually identical to the sorption processes that form the basis of liquid chromatographic separations (p. 80). The choice of solvent, the pH and ionic strength of aqueous solutions, and the chemical nature of the sorbent surface, especially its polarity, are all of importance in controlling the selectivity and efficiency of an extraction. 

As mentioned above, most MIPs are synthesized in organic solvents to preserve the hydrogen and electrostatic interactions between template and monomer. However, for the application to solid-phase extraction (SPE) where the target is most of the time in water samples or in biological fluids, a lot of studies have been carried out to examine the influence of binding media parameters (solvent polarity and composition, buffer pH, concentration, ionic strength, etc.) with the aim of attenuating non-specific adsorption of the analyte due to hydrophobic interactions which predominate in such media. For a recent review, see Tse Sum Bui and Haupt [95]. 

Solid-phase extraction is a sample preparation technique that has been derived from liquid chromatography technology and has been applied extensively to the analysis of biological samples as well as pharmaceutical products. It is a step gradient technique in which the analyte, dissolved in a weak solvent, is retained on a stationary phase and subsequent additions of various moving phases of increasing solvent strength results in selective and controlled elution of the interferences and analytes. 

Pipet the desired amount of solvent into the reservoir space above the adsorbent. Draw the solvent through very slowly. Minimum elution volume is two holdup volumes. The amount and strength of the elution solvent must be determined experimentally and depends on the objectives of the solid phase extraction (Note 11). 

To clean up their samples for reverse phase HPLC analysis. Van Beek and Blaakmeer (1989) investigated the use of C-18, C-8, C-2, cyclohexyl, phenyl, and CN solid phase extraction columns. No improvement of selectivity between limonin and interfering components in grapefruit juice was found. It was reported that the only difference is the elution strength of wash solvent and limonin eluent. Acetonitrile-water mixtures gave better results than methanol-water mixtures. 

Polyclonal antibody Pu e-and-trap Quiescent solution Radioimmimoassay Relative affinity Reversed phase Solid-phase extraction Solid-phase microextraction Solubility Solvent extraction Solvent strength Stationary phase Thin-layer chromatography Titer... 

Solvent strength A measure of the ability of a solvent to elute a material in solid phase extractions or chromatography, based on native polarity. 

The complexity of sample preparation depends on the nature of both analyte and matrix. The nature of the solvent used for the final extract is also important if LC-MS is used insofar as it must have a solvent strength that is no higher than that of the mobile phase into which the extract solution is injected in order to maintain chromatographic efficiency. Sample preparation methods can be categorized based on analyte stability and on the nature of the matrix, particularly its physical phase (liquid, solid or gas). In the majority of cases the final prepared sample is presented to the chromatograph as a liquid. 

The solubility of a liquid component in a near-critical solvent depends on a number of factors. These include solute volatility and the number and strengths of the solute/solvent and solvent/solvent molecular interactions in the solvent-rich phase and of the solute/solvent and solute/solute interactions in the phase being extracted. The occurrence of these interactions is density-dependent. The situation for a solid solute is conceptually rather simpler since the solvent will not normally dissolve in the solid phase. 

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