Quantitative analysis of alpha-D-glucose in an ionic liquid by using infrared spectroscopy.

The applicability of infrared (IR) spectroscopy for quantitative concentration measurements in mixtures of carbohydrates and ionic liquids (ILs) is investigated. The compound 1-ethyl-3-methylimidazolium acetate, [EMIM][OAc]-an "enzyme-friendly" ionic liquid with great application potential in the dissolution of various biomasses-is used as solvent in combination with alpha-D-glucose. Our study establishes a new way to monitor the concentration of sugars in ILs, thus providing a convenient method to follow the kinetics of, for example, enzymatic reactions in [EMIM][OAc]. As a first step, we present the IR spectrum of pure [EMIM][OAc] (this constitutes the first vibrational study of this particular IL). Although numerous lines overlap in the fingerprint region of the spectrum, characteristic features can be assigned to the corresponding vibrational modes of both ions. Secondly, we study different mixtures of the IL with alpha-D-glucose (in the concentration range: 0-20 mass % glucose) and analyze them by means of IR spectroscopy, followed by computational methods, thus demonstrating the great potential of this spectroscopic technique in quantitative measurements.