Polyamide, comprising Nylon-6 derived from caprolactam polymerization and Nylon-66 obtained by the polymerization of adipic acid and hexylene diamine, contains a plenty of acylamino groups in its molecule structure. With these acylamino groups, hydrogen bond can be formed by phenols, acids, quinones and nitro compounds, thereby separating substances that were not capable of hydrogen bond formation. By this method, various compounds can be separated due to their tendency of hydrogen bond formation with polyamide, i.e., adsorption strength.

Researchers from Institute of Process Engineering, Chinese Academy of Sciences achieved the separation of polyphenolic solutes with solvent mixtures of acetic acid and ethanol.Polyamide was tested in terms of several groups of polyphenols with known structure. Phenols (including flavones and tannins) and acids formed hydrogen bond with polyamide via hydroxyl group (or carboxyl group), while quinones via quinonyl group and nitro compounds via nitro-group. Generally, the formed adsorption was stronger if more groups contained in a substance and aromatic nucleus with more conjugated bonds. In addition, less adsorption formed due to the formation of intra-molecular hydrogen bond by adjacent groups. Since the adsorption process occurs in liquid phase, the solvent was involved in this process, and therefore, the separation varied by different mobile phases. This work has been published on "Journal of Separation Science" (Min Gao, Xiaolei Wang, Ming Gu, Zhiguo Su, Ye Wang, Jan-Christer Janson. Journal of Separation Science, 2011, 34 (15): 1853-1858) http://onlinelibrary.wiley.com/doi/10.1002/jssc.201100139/abstract .