Analysis of mono- and oligosaccharides in ionic liquid containing matrices

Ionic liquids (ILs), that is, salts with melting points <100 °C, have recently attracted a lot of attention in biomass processing due to their ability to dissolve lignocellulosics. In this work, we studied how two imidazolium-based, hydrophilic, cellulose dissolving ionic liquids 1,3-dimethylimidazolium dimethylphosphate [DMIM]DMP and 1-ethyl-3-methylimidazolium acetate [EMIM]AcO affect the usually employed analytical methods for mono- and oligosaccharides, typical products from hydrolytic treatments of biomass. HPLC methods were severely hampered by the presence of ILs with loss of separation power and severe baseline problems, making their use for saccharide quantification extremely challenging. Problems in DNS photometric assay and chromatography were also encountered at high ionic liquid concentrations and many capillary electrophoresis (CE) methods did not allow an efficient analysis of saccharides in these matrices. In this paper we describe an optimized CE method with pre-column derivatization for the qualitative and quantitative analysis of mono- and oligosaccharides in sample matrices containing moderate (20–40% (v/v)) concentrations of ILs. The IL content and type in the sample matrix was found to affect both peak shape and quantification parameters. Generally, the presence of high IL concentrations (⩾20% (v/v)) had a dampening effect on the detection of the analytes. IL in lower concentrations of <20% (v/v) was, however, found to improve peak shape and/or separation in some cases. The optimized CE method has good sensitivity in moderate concentrations of the ionic liquids used, with limits of detection of 5 mg/L for cellooligomers up to the size of cellotetraose and 5–20 mg/L for cellopentaose and cellohexaose, depending on the matrix. The method was used for analysing the action of a commercial β-glucosidase in ILs and for analysing saccharides in the IL containing hydrolysates from the hydrolysis of microcrystalline cellulose with Trichoderma reesei endoglucanase Cel5A. According to the results, [DMIM]DMP and [EMIM]AcO] showed clear differences in enzyme inactivation.

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► Reducing saccharides were successfully analysed by CE in ionic liquid matrices.
► Cellooligosaccharides in size up to hexaose were resolved in ionic liquid matrices.
► Modest contents of ionic liquids may improve peak shape and resolution in CE.
► The method was used for studying β-glucosidase action in ionic liquid matrices.