Yoshiyuki Kiso

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.

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.

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.

Complex-forming equilibria in isotachphoresis : II. Evaluation of stability constants of tartrate and citrate complexes

Abstract A computational method is described for the evalution of the thermodynamic stability constants of kinetically labile complexes using the qualitative indexes (RE) observed by means of isotachophoresis. The constants obtained for Mg, Ca, Sr, Ba, Cd and Co-tartrate and -citrate complexes agreed well with previously reported values. The proposed method can be applied to mixed samples, and teh constants obtained in anionic analysis could be also confirmed from cationic analysis in metal-citrate complex systems.

Analysis of a dilute sample by capillary zone electrophoresis with isotachophoretic preconcentration

Abstract A capillary zone electrophoresis (CZE) apparatus utilizing on-line isotachophoretic (ITP) preseparation was constructed and it was shown that the dependence of the migration time in CZE on sample concentration was avoided by ITP preconcentration. The concentration and volume of the test mixture injected by using a microsyringe were in the range of 166–1.66 μM and 0.5–50 μl, respectively. The ratio of the sample volume to the separation column volume (27 μl) was in the range 1.9–185%. Although the migration time in the CZE stage did not change when ITP preconcentration was utilized, if the latter was not used the migration time was prolonged up to 400% non-linearly to the above ratio. The utility of ITP-CZE for the determination of trace components in a matrix was also demonstrated.

Isotachophoretic determination of mobility and pKa by means of computer simulation : VI. Mobility and pKa of sixty anions in methanol

Abstract The isotachophoretic qualitative indices, R E , of 60 anions were measured in methanol as the solvent at several pH values in the range of 7.8–10.7. The absolute mobilities and p K a values were evaluated by the use of a least-squares method utilizing a simulation of the isotachophoretic steady state. The values obtained were compared with those in aqueous solvents, and the differences are discussed. The difference in the isotachophoretic separability according to the solvent used was simulated for several samples and it is suggested that use can be made of this in practical analyses.

Bidirectional isotachophoresis: I. Verification of bidirectional isotachophoresis and simultaneous determination of anionic and cationic components

Abstract Bidirectional isotachophoretic migration was confirmed by the direct measurement of the pH profiles and the boundary velocities of the separated zones. The anolyte used was 10 m M HCl—β-alanine (pH 3.6) and the catholyte was 10 m M KOH-acetic acid (pH 4.8). It was shown that bidirectional isotachophoresis could be achieved with an electrolyte system consisting of a leading electrolyte for an anionic analysis and one for a cationic analysis. The combination was not arbitrary but the pH difference between the anolyte and the catholyte was restricted to keep the effective mobility of the terminating ion not too small. The simultaneous separation and determination of anions and cations in a test mixture were demonstrated on the basis of the time-based zone length measured by the use of a dual detection system.

Simulated quantitative and qualitative isotachophoretic indices of 73 amino acids and peptides in the pH range 6.4–10

Qualitative and quantitative isotachophoretic indices of 73 amino acids, dipeptides and tripeptides were simulated under 24 leading electrolyte conditions covering the pH range 6.4-10. The RE values and time-based zone lengths are tabulated together with the absolute mobility (m0) and pKa values used. The leading electrolyte used was 10 mM HCl and the pH buffers were imidazole, tris(hydroxymethylamino)methane, 2-amino-2-methyl-1,3-propanediol and ethanolamine. The simulated indices will be useful in the assessment of the separability and determination of the listed and related compounds.