Amide-decorated reusable C₁₈ silica-packed columns for the rapid, efficient and sequential separation of lanthanoids using reversed phase-high performance liquid chromatography

The current work focuses on the sequential separation of trivalent lanthanides (except Pm3+) using modified C-18 silica-packed supports through the reversed-phase high-performance liquid chromatography (RP-HPLC) technique. In the current research, four indigenously synthesized amphiphilic aromatic triamide derivatives, namely N-1, N-1, N-3, N-3, N-5, N-5-hexa(alkyl) benzene-1,3,5-tri carboxamide (alkyl = butyl, hexyl, octyl, and decyl), were employed as column modifiers. The results show that the separation of Ln(3+) can be achieved systematically (< 12 min) by tuning the modifiers' functional group and hydrophobic chain and fine-tuning the column modification procedure and separation parameters. The chromatographic studies revealed that the use of 0.168 mmol of N-1, N-1, N-3, N-3,N-5, N-5-hexa(hexyl)benzene-1,3,5-tricarboxamide (HHBTA) coated column and 0.419 mmol of N-1, N-1, N-3, N-3, N-5, N-5-hexa(octyl) benzene-1,3,5-tricarboxamide (HOBTA) modified columns offered excellent separation for the lanthanoids, using 0.1 M alpha-hydroxyisobutyric acid (HIBA), as mobile phase. The separated lanthanoids were quantified by post-column derivatization reaction (after the separation process) using Arsenazo (III) as the post-column reagent by integrating with a UV-Visible detector fixed at 655 nm (lambda(max)). A systematic study on the influence of various analytical features, such as the effect of the modifier's chain length and its concentration, mobile phase composition and pH, was performed and optimized for achieving the best separation protocols.