Different ion maps for the same substance? Glucose analysis by MS Imaging with betaine aldehyde derivatization and NEDC matrix.

Glucose is one of the most essential molecules for sustaining life thus, appropriate and trusted methods of analysis are very welcome. In our study, we have tested two ways of glucose analysis by the MALDI IMS approach: one well-known with NEDC matrix in a negative ionization mode and one developed by us with betaine aldehyde derivatization in positive ionization mode with the aid of CHCA matrix. To our surprise, even though both methods should indicate the localization of the same molecule on adjacent tissue sections and produce the same ion maps, we obtained different results. In this study, we tested the idea that maybe one of the techniques is sensitive to a certain hexose. This would be good news because it would mean having a selective technique for analyzing different hexoses. We performed the dried droplet analyses of glucose, galactose, mannose, and fructose either with betaine aldehyde derivatization or with NEDC matrix and compared the results with the analyses from the tissue. Judging from the MS/MS spectra of analyzed molecules and comparing them with MS/MS spectra from the tissue, it is impossible to distinguish between different hexoses, maybe except fructose. In the article we discussed some ideas that could be responsible for the difference in ion maps of native glucose. Moreover, we highlight the advantages and disadvantages of both analytical approaches. Nevertheless, the question of why ion maps for glucose, obtained by the NEDC matrix and betaine aldehyde derivatization are different, remains open.