Takeshi Hirokawa

Table of isotachophoretic indices. I: Simulated qualitative and quantitative indices of 287 anionic substances in the range pH 3-10

Abstract A simulation of isotachophoretic equilibria has been applied to 287 anions, ,evaluating R E indices for qualitative determination and time-based zone lengths for quantitation under 31 leading electrolyte conditions in the range pH 3–10, using eight different buffers. The R E values may be useful for correcting asymmetric potentials of sensing electrodes for precise R E measurement, assessing the separability of samples and estimating the optimum separation conditions. The zone lengths for 10-nmol samples obtained at a driving current of 100 ,μA may be useful for quantitation.

Isotachophoretic determination of mobility and pKa by means of computer simulation : II. Evaluation of mo and pKa of 65 anions

Abstract A computational method has been applied for the evaluation of mo and pKa of 65 organic and inorganic anions from the qualitative indexes RE. For nine dicarboxylic acids, HOOC(CH2)nCOOH (n  0-8), the RE values have been obtained, and by the use of the least squares method the absolute mobilities have been evaluated. In order to confirm the validity of the proposed method, step heights observed previously by Everaerts et al. have been converted into RE values, and the mo and pKa values evaluated for 58 anions. The agreement between the evaluated and the previously reported values is satisfactory, confirming the utility and the general applicability of the proposed method for the determination of mo and pKa of weak acids and bases.

High-sensitivity capillary gel electrophoretic analysis of DNA fragments on an electrophoresis microchip using electrokinetic injection with transient isotachophoretic preconcentration

The research adopted a single-channel microchip as the probe, and focused electrokinetic injection combined with transient isotachophoresis preconcentration technique on capillary electrophoresis microchip to improve the analytical sensitivity of DNA fragments. The channel length, channel width and channel depth of the used microchip were 40.5 mm, and 110 and 50 microm, respectively. The separation was detected by CCD (charge-coupled device) (effective length=25 mm, 260 nm). A 1/100 diluted sample (0.2 mg/l of each DNA fragment) of commercially available stepladder DNA sample could be baseline separated in 120 s with S/N=2-5. Compared with conventional chip gel electrophoresis, the proposed method is ideally suited to improve the sensitivity of DNA analysis by chip electrophoresis.

Analysis of trace Co in synthetic diamonds using synchrotron radiation excited X-ray fluorescence analysis

Abstract Synchrotron radiation excited X-ray fluorescence analysis was utilized for characterization of trace impurities in synthetic diamonds. Advantage of the energy tunability was fully utilized to evaluate the attenuation of X-rays through the sample, and the absorption corrected X-ray fluorescence yield was utilized for quantitative analysis. Diamonds grown with several types of metallic solvents were investigated, and quantitative analysis of trace Co was carried out. It was found that Co prefers to be dissolved into {1 1 1} growth sector and that Co concentration in the {1 1 1} growth sector decreases one order of magnitude with the existence of Ni in the solvent. XANES spectra of dissolved Co shows characteristic pre-edge feature similar to that reported with the dissolved Ni. Experimental results suggest that both Ni and Co occupy in the similar site in the diamond lattice and that Ni is easier to be dissolved into diamonds.

Another Approach Toward over 100 000-Fold Sensitivity Increase in Capillary Electrophoresis: Electrokinetic Supercharging with Optimized Sample Injection

Electrokinetic supercharging (EKS) is a powerful and practical method for multifold in-line concentration of various analytes prior to capillary electrophoresis (CE) analysis. However, a problem of insufficient sensitivity has always existed when trace analyte quantification by EKS-CE is a target, especially when coupled with conventional detectors. Normally this requires a greatly increased amount of analyte injected without separation degradation. In this contribution, we have shown that it is possible to substantially improve analyte loading and hence CE method detectability by modifying sample introduction configuration. The volume of sample vial was increased (from typical 500 μL to 17 mL), the common wire electrode was replaced by a ring electrode, and the sample solution was stirred. With these alterations, more analyte ions are accumulated within the effective electric field during electrokinetic injection and then maintained as focused zones due to transient isotachophoresis. The versatility of the customized EKS-CE approach for sample concentration was demonstrated for a mixture of seven rare-earth metal ions with an enrichment factor of 500 000 giving detection limits at or below 1 ng/L. These detection limits are over 100 000 times better than can be achieved by normal hydrodynamic injection, 1000 times better than the sensitivity thresholds of inductively coupled plasma atomic emission spectrometry (ICP-AES), and even close to those of inductively coupled plasma mass spectrometry (ICPMS).

Complex-forming equilibria in isotachophoresis

Abstract A theory for kinetically labile complex equilibria in isotachophoresis has been described for the purposes of computer simulation. Simulated ratios of potential gradients, RE = Et/EL, have been obtained for Ca2+ and tartrate ions coexisting with calcium tartrate complexes. The simulated values agreed well with the observed ones and the validity of the simulation has been confirmed. The simulation can be used for the determination of optimal conditions and also for the estimation of stability constants and/or mobilities of complexes.

Complex-forming equilibria in isotachophoresis : VI. simulation of isotachophoretic equilibria of lathanoids and determination mobilities and stability constants of acetate and β-hydroxyisobutyrate complexes

Abstract The istachophoretic separation of fourteen lanthanoids (Ln) was studied using three difeerent electrolyte systems, viz., acetic acid (Ac), β-hydroxyisobutyric acid (HIB) and their mixture, as the complexing agent. A computational procedure based on the least-squares technique was used for the determination of the absolute mobilities of LnAc, LnHIB and Ln(HIB)Ac complexes from the qualitative index RE. The stability constants of Ln(HIB)Ac were also determined. Using the determ constants, the isotachophoretic separation of lanthanoids could be explained by the differences in the effective mobilities accompanied by the different abundances of multi-coordinated complexes.

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.

Isotachophoretic determination of mobility and pKa by means of computer simulation : V. Evaluation of mo and pKa of twenty-eight dipeptides and assessment of separability

Isotachophoretic qualitative indices, RE, for twenty-eight dipeptides were measured in the range pH 7.4-9.6. The absolute mobility, mo, and pKa values were evaluated by the use of the least-squares method, utilizing a simulation of the isotachophoretic steady state. The mo values were newly evaluated and the pKa values were in good agreement with literature values. By comparison of the evaluated mo and pKa values of the dipeptides with those of the constituent amino acids, simple relationships were found which may be used to estimate the mo and pKa values of other dipeptides. The separability of the dipeptides was also evaluated by considering the differences between their simulated effective mobilities. It is concluded that isotachophoresis is very convenient for the separation of dipeptides and their constituent amino acids.

Sensitive determination of anions in saliva using capillary electrophoresis after transient isotachophoretic preconcentration

A transient isotachophoresis-capillary electrophoresis (tITP-CE) system for the determination of minor inorganic anions in saliva is described. The complete separation and quantification of bromide, iodide, nitrate, nitrite, and thiocyanate has been achieved with only centrifugation and dilution of the saliva sample. In-line tITP preconcentration conditions, created by introduction of the plugs of 5 mM dithionic acid (leading electrolyte) and 10 mM formic acid (terminating electrolyte) before and after the sample zone, respectively, allowed the limits of direct UV absorption detection (at 200 nm) to be up to 50-fold improved as compared with CE without tITP. As a result, nitrate and thiocyanate were still detectable at 4.6 and 3.8 microgl(-1), respectively, in 1000 times diluted saliva. The daily variations of anionic concentrations in saliva samples taken from a smoking health volunteer were discussed based on the results of tITP-CE analysis. It was confirmed that the thiocyanate concentration in saliva noticeably increased after smoking. This is apparently the first report on simultaneous quantification of more than four anionic salivary constituents using CE.