Hikaru Okamoto

Operational modes for transient isotachophoretic preconcentration-capillary zone electrophoresis and detectable concentration of rare earth ions.

Operational modes for transient isotachophoretic preconcentration capillary zone electrophoresis (tr‐ITP‐CZE) were studied by using 5 νM and 0.5 νM rare earth mixtures as analytes in comparison with field‐enhanced sample stacking. After examination of several operational modes for tr‐ITP, it was found that tr‐ITP effectively occured even if both the leading electrolyte and the terminating electrolyte were injected after the sample plug. This was explained as the result of a field‐enhanced stacking for both sample components and the leading and terminating ions. The observed theoretical plate numbers were 4–20 times higher than those obtained by normal stacking; and the estimated low limit of detectable concentration of rare‐earth elements (REE) was ca. 0.1 νM which was 2.5 times lower compared to normal stacking. For the 0.5 νM sample, a concentration factor of 20 000 could be achieved after only tr‐ITP.

Trace ion analysis of sea water by capillary electrophoresis: determination of strontium and lithium pre-concentrated by transient isotachophoresis

The applicability of capillary zone electrophoresis (CZE) to ions having relatively low natural occurrences in sea water is limited by methods relatively poor concentration detection sensitivity. A combination of CZE with indirect UV detection and transient isotachophoresis (tITP) pre-concentration was developed to evolve the CZE practical utility towards the quantitative determination of the minor sea water cationic components, strontium and lithium. The ITP stacking criterion at the initial stage of a CZE separation was met by taking a highly mobile sodium, the principle matrix cation, to perform the role of a leading ion, whereas the moderately mobile sample macrocomponents, Ca2+ and Mg2+, acted as the terminating ion. The carrier electrolyte, consisting of 10 mM 4-methylbenzylamine and 1.5 mM citric acid at pH 4.8, was found to be optimal to accommodate both analyte cations in the ITP range and then separate them in the CZE mode, with relative standard deviations for migration times from 0.06-0.15% and for peak areas from 4-8%. The limits of detection were 1.3 mg l(-1) Sr2+ and 0.12 mg l(-1) Li+. The developed method was applied to the analysis of a surface sea water sample and a sea water reference material. The results were in good agreement with those obtained by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and electrothermal atomic absorption spectrometry (ET-AAS).

Change of migration time and separation window accompanied by field-enhanced sample stacking in capillary zone electrophoresis.

When field‐enhanced sample stacking was used in capillary zone electrophoresis (CZE) analysis of cations, the decrease of migration time and the reduction of separation window was observed with increase of sample plug length. A simple equation expressing the migration velocity in the stacking process was derived to explain the above phenomenon. From experiments and theoretical consideration, we confirmed that this effect was caused by the higher potential gradient and larger eletroosmotic flow (EOF) mobility at the sample plug than those at the supporting electrolyte. A mathematical model appropriate for the computer simulation of such a system was studied considering the experimental results, and it was concluded that electroosmotic velocity (veof) should be introduced to the equation of continuity as a constant.