Direct fluorescence detection of ultratrace lanthanide(iii) ions complexed with aromatic polyaminocarboxylate, avoiding quenching of ligand-centered emission, using capillary zone electrophoresis with a ternary complexing technique

Abstract

The ultratrace level detection and the separation of lanthanide ions (Ln³⁺) were achieved using capillary zone electrophoresis with laser induced fluorescent detection (CZE-LIF) using an aromatic polyaminocarboxylate ligand synthesized in our previous work. The ligand forms kinetically stable Ln complexes at the pre-capillary derivatizing step. It effectively avoids quenching processes of the ligand-centered fluorescence through complexation with Ln³⁺ without paramagnetic and heavy atom effects because of the distance between the chelating and the antenna moieties. During the on-capillary separation step, the mother Ln complexes competitively form ternary complexes with the auxiliary ligands, iminodiacetate and citrate, which provide different mobilities for each of the Ln³⁺ complexes. The emissively labeled Ln³⁺ complexes were efficiently separated, based on the ternary complex equilibrium. Since the carrier buffer employed was free from emissive ligands, a high signal to noise ratio was obtained. A lower detection limit of 9.1 × 10⁻¹¹ mol dm⁻³ (15.6 ng dm⁻³, 0.46 attomole as an amount basis) was successfully achieved typically for Lu³⁺ with a simple CZE mode. We propose a combination of a pre-capillary and an on-capillary complexing technique as a method that provides both high sensitivity and high resolution.