Direct Fluorescence Detection of Ultratrace Lanthanide(III) Ions Complexed with Aromatic Polyaminocarboxylate Avoiding Quenching of Ligand-Centered Emission Using Capillary Zone Electrophoresis with Ternary Complexing Technique

Ultratrace level detection and the separation of lanthanide ions (Ln) was 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 and effectively avoids quenching processes of the ligand-centered fluorescence through complexation with Ln without paramagnetic and heavy atom effects because of the distance between the chelating and the antenna moiety. During the oncapillary separation step, the mother Ln complexes competitively form ternary complexes with the auxiliary ligands, iminodiacetate and citrate, which provide different mobility for each of the Ln complexes. The emissively labeled Ln 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 by its silent baseline. A lower detection limit of 9.1 × 10 mol dm (15.6 ng dm, 0.46 atto mole as an amount basis) was successfully achieved typically for Lu with a simple CZE mode. We propose a combination mode of a pre-capillary and an oncapillary complexing technique as a method which provides both high sensitivity and high resolution.