Determination of Glucose and Cellobiose Dissolved in the Ionic Liquid 1-Ethyl-3-Methylimidazolium Acetate Using Fourier Transform Infrared Spectroscopy

The conversion of biogenic carbohydrate feedstock to chemicals or energy equivalents is a promising approach to solve the problem of limited fossil fuel reserves. Some concepts to accomplish these transformations are based on ionic liquids (ILs) due to their ability to dissolve biopolymers, such as cellulose, and even complex biopolymer mixtures, such as wood. However, concerning control of such conversions, a reliable tool for process analytics is required. In this paper we demonstrate the applicability of Fourier transform infrared (FT-IR) spectroscopy to perform quantitative concentration measurements of glucose and cellobiose as two examples of carbohydrates dissolved in the room-temperature ionic liquid [EMIM][OAc] (1-ethyl-3-methylimidazolium acetate). For this purpose, binary mixtures in the range 0–20 wt% have been studied. A previously developed method for the data analysis, which was based on the Beer–Lambert relation, has been universalized by employing empirical correlations between the measured quantity (i.e., extinction) and the carbohydrate concentration. In the entire spectral range under investigation (500–4000 cm−1) numerous individual wave-numbers have been identified, allowing quantitative measurements with high accuracy and precision.