Water-ice has been characterized as a stationary phase for liquid chromatography. Solutes having two or more polar groups are retained on this stationary phase with THF/hexane as the mobile phase, suggesting that multipoint interactions are required for measurable solute retention. Chromatographic separation of phenols or crown ethers on water-ice is possible. The ice surface is expected to provide two different adsorption sites coming from the OH and O dangling bonds. Although the solute partition into the quasiliquid layer is also considered, the dependence of the retention times on the THF concentration implies that the interaction of solutes with the water-ice surface rather than the partition into the quasiliquid layer is responsible for solute retention. A retention model suggests that the number of adsorption sites for a crown ether depends on its ring size, whereas two sites are involved for the retention of phenols having two hydroxyl groups. Although hydroxyl groups can act as both a hydrogen bond donor and an acceptor, the interaction with the ice OH sites, which are exposed to the surroundings in comparison with the ice O sites, is more important. However, when an acyclic polyether is added to the mobile phase, its adsorption onto the water ice surface allows the creation of the O sites that phenols can approach without steric hindrance. In the presence of the polyethers adsorbed on the ice surface, the retention of phenols is enhanced, whereas crown ethers become less retained due to the competitive adsorption of the polyethers.

Rapid freezing of an aqueous electrolyte in liquid nitrogen provides an effective way to fabricate uniform-sized liquid pores with the radius ranging from 0.15 to 3 μm (<1% rsd), corresponding to atto- to femtoliter volumes. The size of liquid pores depends on the temperature, and the concentration and type of a salt incorporated into an original aqueous solution. When the concentration of a salt is kept lower than 20 mM, liquid pores are discretely distributed in an ice matrix. Unlike usual small spaces accommodating liquid water, the pore size is tunable and continuously variable by changing the above experimental parameters. The liquid pore has been utilized as microreactors, in which the fluorescent complexation between Mg(2+) and 8-hydroxyquinoline-5-sulfonic acid (HQS) is studied. Under the optimum condition, fluorescence from Mg(2+) ions in the zeptomol level confined in a liquid pore is detected.

Ice chromatography measurements have revealed anomalous enhancements of crown ether complexation in a liquid phase coexistent with ice. The 4 orders of magnitude enhancement was confirmed for the complexation of dibenzo-24-crown-8 in sub-μm-sized liquid inclusions formed in ice doped with <1 mM NaCl or KCl. This enhancement became less pronounced with increasing dopant concentration.

Water-ice particles simultaneously doped with β-cyclodextrin and a salt enabled chromatographic separation of enantiomers without synthetic processes, and enhanced chiral recognition occurring in the liquid-water phase coexistent with the solid-ice phase.

A liquid phase coexists with solid water ice in a typical binary system, such as NaCl-water, in the temperature range between the freezing point and the eutectic point (t(eu)) of the system. In ice chromatography with salt-doped ice as the stationary phase, both solid and liquid phase can contribute to solute retention in different fashions; that is, the solid ice surface acts as an adsorbent, while a solute can be partitioned into the liquid phase. Thus, both adsorption and partition mechanisms can be utilized for ice chromatographic separation. An important feature in this approach is that the liquid phase volume can be varied by changing the temperature and the concentration of a salt incorporated into the ice stationary phase. Thus, we can control the relative contribution from the partition mechanism in the entire retention because the liquid phase volume can be estimated from the freezing depression curve. Separation selectivity can thereby be modified. The applicability of this concept has been confirmed for the solutes of different adsorption and partition abilities. The predicted retention based on thermodynamics basically agrees well with the corresponding experimental retention. However, one important inconsistency has been found. The calculation predicts a step-like discontinuity of the solute retention at t(eu) because the phase diagram suggests that the liquid phase abruptly appears at t(eu) when the temperature increases. In contrast, the corresponding experimental plots are continuous over the wider range including the subeutectic temperatures. This discrepancy is explained by the existence of the liquid phase below t(eu). A difference between predicted and measured retention factors allows the estimation of the volume of the subeutectic liquid phase.