Aspects on Product Isolation and Purification

There is no doubt that we shall be able to closely approach the theoretical aimin the Merrifield synthesis of quantitative transformations on gel phase. However, we shall never reach this goal exactly under all varying conditions of individual multistep syntheses. Consequently each deviation which was fully discussed in Sect. 2.2 causes the accumulation of synthetic contaminations in the product. 

Besides this fundamental reason one has to realize that the result of even a most accurate multistep synthesis on polymer can be questioned by the chemical reaction necessary to release the final product from its support. Parts of the target sequence can be destroyed and desired protecting groups on side functions may be cleaved. These facts furthermore multiply the possibility for contaminations. Therefore, the overall success of any Merrifield peptide synthesis is inherently related also to the quality of isolation and purification procedures (see for example [168]). 

Most of the refinement problems on peptides obtained from polymer phase are characterized by the molecular similarity of the main product and its contaminations. It is 

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