Mitsuhiko Taga

Separation of lanthanides by capillary tube isotachophoresis using complex-forming equilibria

Abstract Fourteen lanthanide ions have been separated and determined simultaneously by capillary tube isotachophoresis using complex-forming equilbria between 2-hydro- xyisobutyric acid and the lanthanide ions. For simultaneous separation it is necessary for the sample ions to migrate at a higher leading ion concentraton than usual (0.005 or 0.01 mol dm −3 . Only 20 min are required for an analysis and the relative standard deviation of the determination is 1.2-2.5% at the 5-nmol level.

Interpretation of the acid-base equilibrium of humic acid by a continuous pK distribution and electrostatic model

Acid-base equilibria of a humic acid were characterized by considering ionic group heterogeneity and electrostatic effects. The continuous pK distribution model, in which acidic functional groups having two centers of distribution were assumed in the humic molecule, was adapted to the experimental titration data by non-linear least square regression analysis. Excellent curve-fitting was obtained, and two centers of pK distribution (μ1 and μ2) and the total amounts of functional groups (CA1 and CA2) were evaluated. It was suggested that there are strong and weak acidic groups in the humic molecule and that they continuously deprotonate according to their pK distribution. The μ values were evaluated in media of various ionic strength (I = 0.004−1); μ1 (strong groups): 3.4–5.1, μ2 (weak groups): 6.0–7.9, and the ratio of CA1 to CA2 was ca. 5:2. The electrostatic model including the Debye-Huckel theory was adapted to evaluate the intrinsic dissociation constants, pKi,int. From the relationship between the μ values and I12, the intrinsic pKi values of two centers of distributions, μint, could be evaluated; μ1,int: 3.03, μ2,int: 5.12. The intrinsic pK distribution and the species distribution curves were calculated under electrostatic-free conditions. Investigation of Fourier transform infrared spectra and the species distribution curves suggested that the two different types of carboxylic groups would contribute to the pK distribution of each functional group.

Determination of lead by continuous-flow hydride generation and atomic absorption spectrometry: Comparison of malic acid—dichromate, nitric acid—hydrogen peroxide and nitric acid—peroxodisulfate reaction matrices in combination with sodium tetrahydroborate

Abstract A continuous-flow hydride generator is combined with a heated quartz tube atomizeratomic absorption spectrometer system for the trace determination of lead. Malic acid K 2 Cr 2 O 7 , HNO 3 —H 2 O 2 and HNO 3 —(NH 4 ) 2 S 2 O 3 are all effective for plumbane generation by means of sodium tetrahydroborate. The relative merits of these systems are investigated in terms of sensitivity, efficiency of plumbane generation and interferences. The sensitivities (0.0044 absorbance) obtained under the recommended conditions for the three systems are 3.2, 1.7 and 1.1 ng Pb ml -1 , respectively, whereas plumbane generation efficiencies are 33%, 47% and >80%, respectively, for 1 μg Pb ml -1 . Silver, Au, Cu and Cd interfere seriously in all reaction systems. A dithizone extraction and back-extraction method is utilized to eliminate interfering ions, followed by reduction of the resulting solution in the peroxodisulphate system. The proposed method is applied to water samples and NBS 1566 oyster tissue.

Effect of cetyltrimethylammonium chloride on electroosmotic and electrophoretic mobilities in capillary zone electrophoresis

Abstract The effect of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), on the electroosmotic mobility and the electrophoretic mobility of organic anions in capillary zone electrophoresis was investigated. The electroosmotic mobility showed four stepwise changes, including a reversal, with increasing CTAC concentration. The behaviour, especially the reversal of the electroosmotic mobility, was explained by assuming the formation of hemimicelles on the capillary wall. That is, CTAC first adsorbs individually by electrostatic interactions and then begins to associate into hemimicelles by Van der Waals attraction. The formation of hemimicelles changes the surface charge of the capillary wall from negative to positive and causes the reversal of the electroosmotic mobility. The effective electrophoretic mobilities of organic anions such as benzoic acid analogues were also influenced by the CTAC concentration. It was concluded that the behaviour was due to the interaction with hemimicelles on the capillary wall and also ion association with the monomer of CTAC and the interaction of micelles in bulk solution.

Effect of addition of glucose on micellar electrokinetic capillary chromatography with sodium dodecyl sulphate

Abstract Glucose was investigated as a possible additive for the improvement of resolution in micellar electrokinetic capillary chromatography. Addition of glucose to the micellar solution facilitated the complete separation of a mixture of nine nucleosides by both extending the elution range and changing the selectivity. Extension of the elution range can be attributed to an increase in the electrophoretic mobility of the micelle. It is also apparent that glucose selectively reduces the distribution coefficients for solutes containing a hydrophilic functional group. This effect was valuable in the separation of some solutes with hydrophilic functional groups and large capacity factors.

Enzyme sensor for L-lactate with a chitosan-mercury film electrode

SummaryAn amperometric enzyme sensor composed of a mercury film electrode and an enzyme-immobilized chitosan membrane is developed. This biosensor is based on both a mercury film electrode detecting the consumption of dissolved dioxygen following enzymatic reaction, and a chitosan membrane. The latter provides an excellent permselectivity and excludes electroactive interferents. The detection range of this biosensor was 1.0×10−5–3.0×10−4 mol/l and the relative standard deviation, R.S.D. at 5.0×10−5 mol/l was 1.4% (n=3). This biosensor was applied to the direct determination of L-lactate in human serum without pretreatment.

Accumulation voltammetry of copper(II) using a carbon paste electrode modified with di-8-quinolyl disulphide

The accumulation voltammetry of copper(II) was investigated with a carbon paste electrode modified with di-8-quinolyl disulphide (DQDS). The DQDS was reduced to quinoline-8-thiol by applying a suitable potential. Copper(II) was accumulated on the electrode as the copper(II)-quinoline-8-thiol complex at a constant potential in 0.1 mol dm–3 acetate buffer. The reduction peak of the copper(II) complex was then observed at –0.30 V by scanning the potential in a negative direction using the differential-pulse mode. The calibration graph for copper(II) was linear over the range 3 × 10–9–2 × 10–6 mol dm–3 with accumulation for 5 min at –0.05 V. As copper(II) was selectively accumulated on the electrode, the influence of concomitant ions was negligible. The method was applied to the determination of copper(II) in Geological Survey of Japan rock reference materials.

Spectrophotometric determination of small amounts of tellurium with bismuthiol II

A spectrophotomeiric method of determining small amounts of tellurium in acidic media with Bismuthiol II has been studied. The tellurium complex with bismuthiol II is extracted almost quantitatively with chloroform from a 3M hydrochloric acid solution or from a solution buffered at pH 3.5. Up to 25 mug of tellurium can be determined by measuring the absorbance of the yellow complex in the chloroform phase at a wavelength of 330 mmu, after washing the chloroform extract with a buffer solution (pH 7.5) to remove the excess reagent from the organic phase. The effects of diverse ions on the determination of tellurium have also been examined. This method is more simple and more sensitive than the methods proposed by Jankovsky et al. and by Cheng.

Effect of sodium dodecyl sulphate on the measurement of labile copper(II) species by anodic stripping voltammetry in the presence of humic acid

Abstract The addition of sodium dodecyl sulphate (SDS) was found to be advantageous in measuring uncomplexed labile copper(II) species in the presence of humic acid (HA) by anodic stripping voltammetry with a thin mercuy film glassy carbon electrode. If HA is present in the solution, the anodic peak of labile copper(II) species is broadened because of the adsorption of HA on the electrode. However, by adding SDS, a sharp peak was obtained and the peak area increased by about 30% because the adsorption of HA on the electrode was preveted. This was verified by electrocapillary curves in which SDS rather than HA become strongly adsorbed on the electrode. Moreover, this method was applied to the evaluation of copper(II) complexing abilities (conditional ability constants and complexing capacities) of HA by copper(II) titratio. The copper(II) complexing capacities of HA evaluated in the presence of SDS were 16% small values than those in the absence of SDS.

Evaluation of copper(II)-binding ability of humic acids in peat using sulphopropyl-Sephadex C-25 cation exchanger

Abstract A method for the determination of copper(II) complexes with humic acids was developed by batch operation with the cation exchanger sulphopropyl-Sephadex C-25 (C-25). The copper-binding ability (conditional stability constants and copper-complexing capacities) of humic acids which were extracted from peat in Hokkaido was evaluated. A solution containing copper(II) ions and humic acids was shaken with the C-25 exchanger. The copper-humic acid complexes remained in the supernatant and the uncomplexed free copper ion was retained on the C-25. The copper-humic acid complexes were determined by flame atomic absorption spectrometry. The copper-binding ability of nitrilotriacetic acid (NTA) as a model ligand was similarly determined with a Scatchard plot. The conditional stability constant obtained at pH 4.5 was in good agreement with the reported value. The copper-binding abilities of the humic acids from peat were estimated using a Scatchard plot adopting a two-site model. The functional groups in the humic acids which contribute to the complexation with copper were investigated by conductimetric and pH titration, and the relationship between the copper-binding sites and functional groups in the humic acids was investigated.