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Research Area
Development of new methods for the separation and detection of extremely small amount of molecules in nature is the primary mission of Analytical Chemistry. We are focusing on the studies of (i) the kinetics and mechanisms of the liquid-liquid interfacial reaction and (ii) the migration analysis of micro-particles in liquid by using external fields. The liquid-liquid systems have been used for long time for the solvent extraction of metal ions and organic compounds. However, the role of the interface in the solvent extraction has not been elucidated until quite recently. Various new techniques, which we have invented, contributed to elucidate the reaction mechanisms of interfacial reactions. Followings were especially useful.
  1. High-speed stirring method
  2. Centrifugal liquid membrane (CLM) method, CLM/Raman microscope spectrometry and CLM/circular dichroism(CD) spectrometry (1)
  3. Micro-two-phase sheath flow method
  4. Single molecule probing at the interface
  5. Surface enhanced Raman scattering (SERS) from nano-particles at the interface
  6. Second Harmonic Generation-circular dichroism of the liquid-liquid interface (2)
By using these techniques, we have clarified that the specific roles of the liquid-liquid interface are (i) catalytic effect of the interface in the interfacial kinetics such as the solvent extraction kinetics and (ii) the aggregation of hydrophobic molecules or metal complexes at the interface, which formed occasionally chiral aggregates (3). Another important subject we have to challenge is the characterization of micro-particles in liquid. There were very limited methods to analyze a single micro-particle in liquid. We have developed the following migration methods by utilizing external force,
  1. Laser photophoresis (laser scattering force)
  2. Capillary dielectrophoresis (dielectric force)
  3. Micro-magnetophoresis (magnetic force)
  4. Electromagnetophoresis (electromagnetic force)
  5. Nano/micro-gap particle sorting (solid wall surfaces)
Magnetophoretic velocimetry succeeded to measure the magnetic susceptibility of a single micro-particle in solution. Furthermore, magnetophoresis of a particle in air allowed us to measure the magnetic susceptibility and the mass simultaneously (4). This technique is quite promising as a new principle of the magnetic mass spectrometry of micro-particles.
Reference
  1. S.Wada, K.Fujiwara, H. Monjushiro, and H. Watarai, Anal.Sci., 20, 1489 (2004).
  2. K. Fujiwara, H. Monjushiro and H. Watarai, Chem. Phys. Lett., 349 (2004).
  3. H. Watarai et al. (eds.), Interfacial Nanochemistry, Kluwer Academic/Plenum, NY, 2005.
  4. K.Watanabe, M. Suwa, and H. Watarai, Anal. Sci., 20, 1483 (2004).