Highly sensitive determination of lanthanides by capillary electrophoresis with direct visible detection after precapillary complexation with aromatic polyaminocarboxylate and additionally applying dynamic ternary complexation with nitrilotriacetic acid

A newly synthesized aromatic polyaminocarboxylate (NBD-ABEDTA, H(4)L) was applied to precapillary derivatizing capillary electrophoresis as a chelating reagent for lanthanide ions (Ln(3+)). The Ln-L complexes provide both kinetic stability on dissociation due to their methyl-EDTA coordinating structure, and high light absorptivity (epsilon(max) = 2.4 x 10(4) cm(-1) mol(-1) dm(3)) in the visible region at 469 nm thanks to their nitrobenzofurazan moiety. A ligand was employed for capillary zone electrophoresis based on a unique concept: both precapillary and dynamic on-capillary complexation were carried out on one center-metal ion to achieve high resolution. As a ternary complex-formation agent, iminodiacetate (IDA), bound to the mother complex (Ln-L), was added to the carrier buffer solution. The carrier buffer solution of 9.5 mmol.dm(-3) (pH 9.45) borate and 33.5 mmol.dm(-3) IDA, drastically improved the resolution among Ln(3+) ions. Each of the Ln complexes was effectively separated, except for Pr-Sm. Furthermore, the absence of L from the carrier solution, which stabilizes the baseline fluctuation, provided low LOD (typically 4.2 x 10(-7) mol.dm(-3)). This strongly suggests that Ln-L complexes are kinetically stable even with a large excess of IDA. Quite unexpectedly, the order of migration differs from that of the atomic number, inverting at Nd. This is due to the effect of the cavity size of the residual coordination sites on the ternary complexation and the electronic density of Ln(3+).