Biased spectroscopic protein quantification in the presence of ionic liquids

Owing to their unique physicochemical properties, ionic liquids have gained much recognition as solvents or co-solvents in a wide variety of biochemical applications. In the context of protein analytics, four similar 1-alkyl-3-methylimidazolium-based ionic liquids have been analysed for their applicability as co-solvents. Spectroscopic bovine serum albumin (BSA) quantification experiments in the presence of ionic liquids were performed and for two ionic liquids a concentration-dependent effect has been found that can lead to biased protein quantification. It could be shown that the biased spectroscopic analysis of the tested ionic liquids is dependent on the length of the alkyl side chain (>C₄) of the 1-alkyl-3-methylimidazolium-based cation, and the chaotropicity of the anion. Once accounted for and properly calibrated when using spectroscopic methods, these effects can be avoided thus facilitating correct protein quantification in the presence of ionic liquids.