Spectroscopy microdroplets, single

In the second technique, two streams of microdroplets (about 100 p.m diameter, 40 kHz generation frequency, 15 ms velocity) collide to form a single droplet stream, which is observed by Raman spectroscopy. The mixing time is 200 p.s. 

In this review, we describe a laser trapping-spectroscopy-electrochemistry technique as a novel methodology for studying single microdroplets in solution and, demonstrate recent progress in the research on electron transfer and mass transfer across a microdroplet/solution interface in special reference to a droplet size dependence of the process. 

The laser trapping-spectroscopy-electrochemistry technique is unique in that simultaneous three-dimensional manipulation and spectroscopic/elec-trochemical measurements can be conducted for individual microdroplets in solution. Although the technique is highly useful for studying single microdroplets, its applicability and limitations have not been well documented until now. Therefore, before discussing detailed chemistry of single droplets in solution, we describe briefly the characteristics of the technique. 

In Sections III and IV, we described droplet size dependencies of the ET and MT rates across microdroplet/water interfaces. Such experiments on single droplets are possible by the laser trapping spectroscopy-electrochemistry technique alone. Besides these experiments, the technique is also highly useful in controlling a reaction efficiency in microdroplets [99,100]. In this section, we describe electrochemically induced dye formation reactions across microdroplet/water interface and demonstrate control of the dye formation reaction yield in micrometer dimension. The effects of microenvironments and additives (surfactant or stabilizer) on dye formation reactions are also described. 

The laser trapping-spectroscopy-electrochemistry technique, capable of single microdroplet measurements, is shown to be indispensable in elucida-... 

Ion-pair extraction of an anionic surfactant with a cationic dye such as methylene blue from water into oil is often used for the quantitative analysis of the surfactant in water [57,58]. The surfactant concentration in water is then determined as the dye concentration in the oil or water phase by conventional absorption spectroscopy. Synthetic surfactants such as sulfates and sulfonates completely dissociate in water even at low pH. On the other hand, the association of fatty acid salts (traditional soaps) with H" " depends on the pH. Therefore, the quantitative analysis of surfactants in water is performed by the ion-pair extraction at various pHs. Although quantitative analysis and thermodynamic studies have been already reported for the anionic surfactant/cationic dye extraction, kinetic analysis of the ion-pair extraction has been rarely reported and the extraction mechanism is not discussed in detail. In this section, we describe the kinetic analysis of the extraction of a dodecyl sulfate anion with methylene blue as a typical example using the single microdroplet manipulation and microabsorption methods [59]. In particular, the pH dependence of the ion-pair extraction is discussed. 

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