Abstract: The apparatus includes an endless belt of nickel having a surface profile comprising an array of cavities such that any liquid layer deposited on the surface is keyed into the surface and constrained against movement relative to the surface. A liquid comprising solute and solvent is deposited as a layer on the belt from a nozzle. A first heater evaporates the solvent but leaves the solute. A second heater evaporates the solute which is then collected and fed to an analyzing device. The profile of the belt is particularly conducive to constraining a liquid on the belt and ensuring uniform evaporation upon heating.