Polyamide 6 (ε-polycaprolactam) Polyamide 6 (ε-polycaprolactam) is widely used for the chromatographic separation of natural products with phenolic functional groups, e.g., flavonoids, anthraquinones, flavonols as well as carboxylic acids and aromatic nitro compounds. Polyamide is produced by hydrolytic polymerization of ε-caprolactam. It possesses a melting temperature of above 200 °C. A special characteristic of this material in comparison with silica and other resins is its water adsorption properties. The saturation concentration at 23 °C is about 9.5 %. As stationary phase polyamide can be used in normal or reversed phase mode due to its medium polarity. The separation mechanism is mainly based on hydrogen bonding. The elution strength of the solvent increases in the following order: water < methanol < acetone < diluted aq. sodium hydroxide solution < formamide < dimethylformamide. Polyamide exhibits a good resistance towards aliphatic hydrocarbons (e.g., hexane, heptane), aromatic hydrocarbons (e.g., naphthalene, toluene), esters (e.g., ethyl acetate), ethers (e.g., diethyl ether, dioxane), aldehydes (e.g., formaldehyde), ketones (e.g., acetone) and alcohols (e.g., ethanol, isopropanol, methanol). Polyamide is stable within the pH range of 3 to 9 at 25 °C.
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