Kenji Chayama

Application of capillary electrophoresis to the analysis of inorganic ions in environmental samples

A comprehensive review is presented of the state-of-the-art of capillary electrophoresis for application to the analysis of inorganic species, mainly ions, in environmental samples. This brief review covers the developments principally in sensitivity and matrix interference for the determination of inorganic ions in the following samples: drinking, mineral, surface, and ground waters, rainwater, snow, seawater, brine and waste waters, aerosol, and others. References published mainly from 1995 to 1997 were summarized in this review.

Longitudinal study on selenium content in human milk particularly during early lactation compared to that in infant formulas and cow's milk in Japan

239 samples of human breast milk were collected from 36 healthy Japanese women. Selenium content of the samples was determined mainly by highly sensitive fluorometric analysis with 2,3-diaminonaphthalene. The highest selenium content, 247 micrograms/kg, was found on the first day postpartum. The arithmetic mean of selenium content was higher in colostrum (< 4 days) 47 micrograms/kg (SD 42, n = 116) than in transitional milk 24 micrograms/kg (SD 13, n = 87) or in mature milk (> 10 days) 10 micrograms/kg (SD 4, n = 36). Selenium content was also determined for six brands of commercial infant formula powder (32-58 micrograms/kg) based on cows milk, seventeen brands of cows milk (10-25 micrograms/kg) and eight brands of powered cream for cofee (9-162 micrograms/kg). The average selenium content was significant lower in the liquid formula prepared for infant lactation, 6.0 micrograms/L, than in the human colostrum and transitional milk. The dietary selenium intake of newborns fed on colostrum is estimated to be in the range of 2-12 micrograms per day.

Separation of bisphenol A and three alkylphenols by micellar electrokinetic chromatography.

Analytical conditions of pH, surfactants, and additives were investigated for the simultaneous separation of bisphenol A and alkylphenols by micellar electrokinetic chromatography. Reproducibility of migration time was improved at higher pH (pH 8.0). When five surfactants having linear alkyl chains or four bile salts were used, the separation of hydrophobic phenols and 4-nonylphenol isomers was not achieved. In order to improve the separation, the use of additives with sodium dodecyl sulfate solution was investigated. The separation of hydrophobic phenols was improved by the addition of organic solvents, however, isomers were not separated. Their separation was achieved by the addition of beta- or gamma-cyclodextrin.

Thermosensitive gels incorporating polythioether units for the selective extraction of class b metal ions

Novel temperature-responsive copolymers of N-isopropylacrylamide and monoaza-tetrathioether derivative, were synthesized for the selective extraction of soft metal ions such as silver(I), copper(I), gold(III) and palladium(II) ion. The ratio between N-isopropylacrylamide group and monoaza-tetrathioether group in the copolymer was determined. The ratio between N-isopropylacrylamide group and monoaza-tetrathioether group varied in the range of 66:1-187:1. Each lower critical solution temperature (LCST) of the polymer solution was determined spectrophotometrically by the relative absorbance change at 750 nm via temperature of the polymer solution. Metal ion extraction using the copolymer with appropriate counter anions such as picrate ion, nitrate or perchlorate ion was examined. Soft metal ions such as silver(I), copper(I), gold(III) and palladium(II) ion were extracted selectively into the solid polymer phase. The extraction efficiency of a metal ion such as silver ion increased as the increase of the ratio of the monoaza-tetrathioether group to N-isopropylacrylamide group in the polymer. The quantitative extraction of class b metal ions as well as the liquid-liquid extraction of metal ions with monoaza-tetrathioether molecule was performed.

Quantification of Ag(I) and kinetic analysis using ion-pair extraction across a liquid/liquid interface in a laminar flow by fluorescence microscopy

To analyze the kinetics of complicate ion-pair extraction, we have utilized a microfluidic approach and fluorescence detection. We have already developed a Ag(I)-specific thia-crown ether as an ion-association reagent. Furthermore, a fluorescent anion was added to detect the generated complex of Ag(I), ion-association reagent, and the counteranion in the ion-pair extraction system. A two-phase laminar flow consisting of an aqueous liquid and an organic liquid in a microchannel was formed, and the relationship between the initial conditions and reaction rate was examined. The microfluidic device could realize a spatiotemporal approach to solvent extraction, because the traveling length along the interface corresponded to the reaction time. The rate-determining step was estimated according to ion-pair formation behavior. Furthermore, due to the miniaturized reaction volume in the microchannel, rapid extraction of Ag(I) was achieved. The microchannel width was optimized to carry out the rapid extraction of A...

Pyridinium-based Task-specific Ionic Liquid with a Monothioether Group for Selective Extraction of Class b Metal Ions

A pyridinium-based task-specific ionic liquid (TSIL) with a monothioether group, [3-TPPy][NTf2], extracted typical class b metal ions, such as Ag(I), Cu(I), Pd(II), and Pt(II), in high selectivity. It was found that the composition ratio of the extracted Ag(I) and Cu(I) species depended on the TSIL concentration, and that TSIL extracted these metal ions through mono-S-coordinated complex formation at low TSIL concentrations. [3-TPPy][NTf2] can be recycled in the extraction-recovery process, which is of a great advantage for practical use in environmentally benign separation methods.

Fabrication of Electrophoretic PDMS/PDMS Lab-on-a-chip Integrated with Au Thin-Film Based Amperometric Detection for Phenolic Chemicals

A new microfluidic device with a fully integrated electrochemical detection (ECD) system was fabricated using soft lithography. The electrophoretic device made of polydimethylsiloxane (PDMS) comprises an off-channel ECD with a narrow channel decoupler using a duplex replication process. We fabricated a PDMS device which was composed of a PDMS microchannel and a PDMS-coated glass integrated with Au thin-film based electrodes, using an original fabrication process. As an application of the fabricated device based on microchip capillary electrophoresis with ECD, we investigated the simultaneous detection of phenolic chemicals, known to be endocrine disruptors. We achieved simultaneous detection of 4-t-butylphenol and bisphenol A using the micellar electrokinetic chromatographic (MEKC) mode.