Influence of the Lipophilicity of an Ion‐Pairing Reagent on Metal Ion Separation using Ion‐Pair HPLC

Abstract

Tetraalkyl ammonium salts (TAAS) of a wide range of lipophilicities are used as ion‐pairing reagents for simultaneous separation of proposed anionic metal complexes [M (H₂PO₄) ₃]⁻ of U(VI), Fe(III), and neutral Cu(II) using reversed‐phase ion pairing high performance liquid chromatography (RPIP‐HPLC). Tetramethylammonium bromide, tetraethyl ammonium chloride, and tetrapropyl ammonium bromide, due to their low hydrophobicities, are unable to separate U(VI) and Fe(III). Tetrabutyl ammonium perchlorate has separated the three metal ions. Tetrahexyl ammonium bromide, tetraheptyl ammonium bromide, and tetraoctyl ammonium bromide have enhanced resolution for the metal ions, but analysis time was prolonged due to the strong retention of nitrate ion. Also, equilibration time with the stationary phase increases with the increase in carbon atoms in the IPR. The potential of varied carbon containing IPRs has been compared for the analysis of U(VI) in simulated standards. The detection limit and RSD for Cu, Fe, and U are 2, 0.5, and 2 ppm and 4, 5, and 3.3%, respectively.

Keywords:

• Lipophilicity
• Ion pairing
• Metal ions
• HPLC