Separation by Exclusion
Exclusion chromatography can also remove large molecular weight materials from a complex sample matrix. Using a stationary phase of appropriate pores size, substances larger than the pores will be eluted at the interstitial volume of the column and very small molecules that penetrate all the pores will be eluted at the dead volume of the column. Thus, proteins will elute first, at the solvent front, and the smaller molecules elute at a retention volume equivalent to the interstitial volume plus the pore volume. This method is used for the sample clean-up of materials of biological origin which often contain many biopolymers. Separation by exclusion is also a very gentle process that can be easily automated.
Solvent Extraction
Solvent extraction is used for both solids and liquids but has been largely superseded for liquids by solid state extraction.
One type would be for a solvent that was denser than the sample liquid and one that would be for a solvent that was lighter than the sample liquid. One type would be for a solvent that was denser than the sample liquid and one that would be for a solvent that was lighter than the sample liquid. An example of the two types of continuous extractors is shown in figures 15 and 16.
Figure 15. The Continuous Liquid Extractor Where the Liquid Sample is Less Dense than the Extraction Solvent
