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Reactions without walls

Levitating droplets of ionic liquids might sound like a magical illusion, but scientists have found real benefits in using these solvents for containerless chemistry.

Drops of ionic liquids are suspended in mid-air by ultrasound waves

The time and cost savings given by the miniaturisation of laboratory techniques have fuelled their increasing popularity in recent years. But loss of sample through adsorption to the reaction container’s walls can be a problem when working on a small scale.

Bernhard Lendl at the Vienna University of Technology, Austria, and colleagues have overcome this problem by dispensing with the reaction vessel altogether. Using levitated droplets of an ionic liquid as a reaction medium, the team monitored a containerless reaction using Raman spectroscopy, an analytical technique that provides detailed molecular and structural information.

The researchers suspended their samples in mid-air by acoustic levitation, which uses an ultrasonic wave to lift up tiny droplets, just nanolitres in volume. The stable levitation of liquid droplets is normally difficult if the solvent evaporates too quickly, but the fact that ionic liquids are non-volatile makes them ideally suited to this technique.

Lendl and colleagues say the technique could be used to levitate an array of droplets so that a range different reactions or reaction conditions can be monitored at the same time.