Design of Analytical Systems Based on Functionality of Doped Ice

Abstract

43 IntroductionWater has received special attention from researchers in fundamental and practical sciences because it has various unique physicochemical properties, and is indispensable for sustaining terrestrial life.1,2 Although ice is also a material of scientific interest, much less attention has been paid to this solid material than to its liquid counterpart. The same holds true for analytical chemistry. While water has been used as one of the most important solvents, in which a number of analytical reactions occur, 3,4 positive uses of ice for analytical purpose have been few.It has been known that ice is involved in a number of environmental reactions and plays important roles e.g. in the circulation of some molecules of atmospheric importance, such as NO, NO2, and HONO. 5 Ice also adsorbs compounds, such as HCl, and facilitates their reactions on its surface. 6 These roles of ice in the global environment have led to ideas that novel analytical systems can be designed utilizing the chemical properties and functionality of ice. We first developed ice chromatography, in which ice is used as a chromatographic stationary phase.7-10 Various compounds can be separated by this method though there is a limitation in its separation capability. The optical properties of ice are also remarkable; it is transparent over a wide wavelength range, from UV to visible region, and is a rare solid material that has a lower refractive index than do usual liquids. We utilized this useful optical property of ice to fabricate a liquid-core ice-cladding optical waveguide. 11Not only pure ice but also ice involving some impurity is of analytical use. Salt is a common impurity found in natural ice. Such salt-doped ice can be prepared in the laboratory in such a simple way that an aqueous salt solution is frozen. The liquid water phase coexists with ice (WPI) at the temperature higher than the eutectic point of the system. Figure 1 shows a fluorescence micrograph of KCl-doped ice containing fluorescein to visualize the WPI. Interestingly, fluorescent spots are discretely distributed in the ice matrix, suggesting that liquid inclusions are isolated rather than interconnected. We have found that the number density of the liquid inclusions is constant and independent of the type of salt incorporated in ice and its concentration. Ice plays an important role for the circulations of some compounds in the global environment. Both the ice surface and the liquid phase developed in a frozen solution are involved in such reactions of the molecules of environmental importance. This leads to the idea that ice can be used to design novel analytical reaction systems. We devised ice chromatography, in which ice particles are used as the liquid chromatographic stationary phase, and have subsequently developed various analytical systems utilizing the functionality of ice. This review focuses our attention on the analytical facets of ice containing impurities such as salts; hereinafter, we call this "doped ice". The design of novel separation systems...

Fluidic Grooves on Doped-Ice Surface as Size-Tunable Channels

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“…We have reported various separation and reaction systems using frozen aqueous solutions. 18 When an aqueous solution is frozen, solutes are expelled from ice and concentrated in a freeze concentrated solution (FCS). The FCS coexists with ice at temperatures higher than the eutectic point, and its volume is predictable from the equilibrium freezing point depression curve of the system.…”