The low sensitivity of simple CZE for detecting metal ions is a long-standing problem even when an LIF detection system is employed. We have successfully achieved an ultrasensitive CE-LIF using a simple CZE mode (typical detection limit: 10(-11)-10(-10) mol/dm(3)). Both the design of a newly synthesized ligand and the combination of a precapillary derivatizing technique with an on-capillary ternary complexing technique have enabled us to achieve this extremely low LOD and high resolution of large metal complexes. The direct fluorescent detection of the paramagnetic metal ions was achieved for the first time despite their intrinsic fluorescent quenching nature. The fluorescent ligand (L) consists of a polyaminocarboxylate chelating moiety, a strongly emissive fluorescein moiety and a spacer connecting the two portions. The migration behavior of various metal-L complexes was investigated. The resolution among the complexes was improved by the introduction of a ternary complex equilibrium of the kinetically stable mother complexes with OH(-) ion. The analytical potential of our simple system was examined, and it was proved that the system was one of the most sensitive methods without the need for any preconcentration process.
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+).
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