Development of a carbohydrate silylation method in ionic liquids for their gas chromatographic analysis

This paper reports on the feasibility of silylation of low molecular weight carbohydrates dissolved in different ionic liquids (ILs) for their further analysis by gas chromatography (GC). Derivatization reagents (nature and amounts), temperature and time of reaction and stirring conditions were evaluated for different carbohydrates (i.e., glucose, mannose, fructose and lactose) dissolved in 1-ethyl-3-methylimidazolium dicyanamide [EMIM][DCA]. Evaluation of conformational isomerism of glucose dissolved in [EMIM][DCA] revealed the effect of the time of dissolution in the equilibration of α- and β-furanoses (up to 3% and 6%, respectively, after 70h of incubation) and that 21h sufficed to obtain results similar to those provided by the reference method involving pyridine. Once optimized, the proposed derivatization procedure provided satisfactory yields (i.e., close to 100%) using 100μL of trimethylsilylimidazole (TMSI) at mild conditions (25°C) for a relatively short time (1h) for most of the investigated carbohydrates. Under these experimental conditions, linear responses (i.e., R2 better than 0.974) were obtained in the tested range of 0.25-1mg of the derivatized target compounds. Other reagents, such as N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)+1% trimethylchlorosilane (TMCS), were successfully used under ultrasonic conditions for aldose monosaccharides and disaccharides derivatization, while BSTFA was useful for ketose monosaccharides. The possibility of using the proposed method for the derivatization of selected carbohydrates dissolved in different ILs and the efficiency of the method applied to the analysis of carbohydrates present in real samples (fruit juices) have also been investigated. © 2013 Elsevier B.V.This work has been funded by Ministerio de Ciencia e Innovación (project AGL2009-11909), Ministerio de Economía y Competitividad (project CTQ2012-32957) and Comunidad Autónoma of Madrid (Spain) and European funding from FEDER program (project S2009/AGR-1464, ANALISYC-II). L. Ruiz-Aceituno is supported by CSIC by a JAE-Pre grant, co-financed by the European Social Fund (ESF).Peer Reviewe