Experimental apparatus made from ice can be used as detecting systems for solvent extraction and chromatography, claim Japanese scientists. The apparatus is cheaper, more readily available and more environmentally friendly than current equipment, they say.

Light guiding through a liquid-filled channel surrounded by an ice cladding

Tetsuo Okada and colleagues at the Tokyo Institute of Technology used ice to make a liquid-core waveguide, a device for guiding light through liquid-filled channels. Guiding light through liquids is difficult because they have low refractive indices, meaning that they slow down the speed of light. But if the liquid is surrounded by cladding with a lower refractive index, the cladding reflects the light back into the liquid, keeping it on course through the channel without significant loss of intensity.

'Most current liquid-core waveguides are fabricated with Teflon AF-2400 [a fluoropolymer plastic] but it adsorbs various substances on its surface and is damaged even by weak mechanical contact. It also has a high cost,' explains Okada. 'Water-ice is much less expensive and, of course, is environmentally friendly.'

Okada made an ice chip with a thin tunnel running through it. He injected a liquid into the tunnel and shone light through it. He showed that the ice cladding, which has a lower refractive index than most solvents, was better at guiding light than a previously reported Teflon AF-coated glass microchip.

Purnendu Dasgupta, an expert in analytical chemistry at the University of Texas at Arlington, describes the study as 'a fascinating piece of work' that offers 'intriguing possibilities for an ambitious experimenter'. 'In general, we think little about properties of substances other than the form we commonly encounter them in. It makes one wonder what the refractive index properties of some other frozen liquids may be,' he comments.

Okada used the waveguide for ice chromatography, where different compounds in a sample separate out according to their affinity for ice. However, he found that the aqueous core caused the light intensity to fluctuate. 'To prevent such instability, the experimental conditions, such as the type of liquid in the core, its concentration, and working temperature, should be carefully optimised,' says Okada.

Colin Batchelor 

Link to journal article