The separation of very similar substances such as isomers has proved as challenging. (U)HPLC phases with a high steric selectivity are required for such analyses. In this application note the fatty acid methyl esters methyl linolenate and methyl γ-linolenate are separated using YMC-Triart C18 ExRS. Due to its exceptional high hydrophobicity and steric selectivity, YMC-Triart C18 ExRS is especially suitable for the analysis of these hydrophobic isomers.
When using typical UHPLC dimensions (150 x 3 mm ID) both compounds could not be fully separated, even though an optimised mobile phase consisting of 30% water/acetonitrile (50/50) and 70% tetrahydrofuran was used. To further improve and achieve baseline separation an extended separation length of 250 mm is required. As this length is usually not available for UHPLC columns a coupling of two standard columns can easily solve this issue. By coupling of 150 mm and 100 mm length columns the resolution could be improved from 1.1 to 1.6 (see fig. 2).