ИСТИНА

Two popular liquid chromatography modes have something in common. The most common mixed-mode reversed phase/ion-exchange high performance liquid chromatography (HPLC) combines major impact of hydrophobic interactions and additional contribution of electrostatic interactions in retention of ionised organic molecules. On the contrary, electrostatic or ion-exchange interactions define the retention of organic ions in ion chromatography (IC), while hydrophobicity is playing auxiliary role in attuning separation selectivity. There is a big number of organopolymer based ion-chromatographic columns, where hydrophobic interactions are practically ignored by the majority of separation scientists. Hydrophobic interactions in ion-exchangers depend on the properties of matrix, density of charged functional groups at the surface of adsorbent and hydrophobicity of functional groups. The aim of this investigation was to develop a universal approach for the characterization of hydrophobic properties of ion-exchange resins with emphasis on correct evaluation of their capability to retain organic ions of different hydrophobicity. With a growing interest to the use of IC for the separation of pharmaceuticals, their by-products and etc., it becomes important to know the hydrophobicity of ion-exchange stationary phases used. The possible combined effect of these two types of interactions on retention of organic ions is also under scrutiny. The regularities of the retention of different groups of negatively (carboxylic and alkylsulfonic acids), positively charged organic molecules (amines and diamines) and aromatic amino acids were studied for the set of 25 anion-exchange columns and 18 cation-exchange columns produced by various manufacturers. The role of hydrophobic, electrostatic and π-π interactions in retention of organic cations, anions and zwitterions is revised. A new effect showing a significant contribution of polarisation organic ions at the surface of ion-exchangers into retention of organic ions is discovered.