Ionic liquid matrices for MALDI-TOF-MS analysis of intact glycoproteins.

2,5-Dihydroxybenzoic acid (DHB) has been demonstrated to be a more suitable matrix than 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SA) to obtain reliable molecular mass values of intact glycoproteins because it prevents sugar fragmentation. Lack of spot homogeneity during the crystallization step was prevented by drying the sample-matrix mixture under vacuum conditions. Nevertheless, this sample-matrix preparation procedure requires a specific experimental setup and may be time-consuming. In this work, we investigated the effectiveness of different ionic liquid matrices (ILMs) with SA and DHB on the ionization of a set of intact glycoproteins with several degrees of glycosylation. The obtained results demonstrate that some of the tested ILMs allow detection of the studied intact glycoproteins. Furthermore, the selected optimum conditions solve the reproducibility issue of using the DHB as a solid matrix without the vacuum drying method and, surprisingly, avoid sugar fragmentation when both SA and DHB were used as ILMs.