Dynamic chelation ion chromatography of transition and heavy metal ions using a mobile phase containing 4-chlorodipicolinic acid

The chromatographic behaviour of selected transition and heavy metal ions, the lanthanides, uranium and aluminium, on a neutral polystyrene–divinylbenzene (PS–DVB) stationary phase (7 μm Hamilton PRP-1) dynamically modified with 4-chlorodipicolinic acid, was investigated to evaluate retention characteristics. Complicated retention factor against pH plots were found for these metals demonstrating changes in retention order. It was concluded that complexation between the metal ions and the ligand adsorbed on the resin was strongly influenced by the decrease in dynamic loading with increase in pH, coinciding with changes in the metal-to-ligand ratio in the mobile phase. Possible reversed-phase interactions between metal–chlorodipicolinic acid complexes and the hydrophobic PS–DVB stationary phase also could not be ruled out. An eluent of 0.25 mM chlorodipicolinic acid, 1 M potassium nitrate at pH 2.2 was suitable for the separation of seven transition and heavy metal ions in under 20 min on a 250×4.6 mm column (with 50-mm guard column), determined in a certified water sample with good accuracy (R2≥0.994) and reproducibility (RSD 1–4.2%). Pb(II), Cd(II) and Cu(II) were additionally analysed in <10 min in a more complicated certified rice flour matrix, using the same eluent but adjusted to pH 1.5, again with good accuracy (R2≥0.998) and reproducibility (RSD 0.48–1.38%).