OrbiSIMS spatially resolves isomeric molecules on surfaces

Orbitrap secondary ion mass spectrometry (OrbiSIMS) is growing in popularity in a wide range of applications in life sciences and materials science, with the ability to provide high confidence in molecular identification simultaneously with high confidence in localisation (spatially at the microscale and at the nanoscale within a layer). In OrbiSIMS, transmission of secondary ions depends on two key parameters, the target voltage and helium gas pressure in a cooling cell. _{Here, we show that controlling these parameters gives OrbiSIMS the capability to couple phenomena that enable the separation of molecules based on their dissociation patterns and transmission after gas-phase collisions, which are related to molecular structure. We show that these phenomena can be leveraged and used analytically to take OrbiSIMS beyond the limitations of the mass scale and spatially resolve the signal of mixtures of structural isomeric trisaccharides (raffinose, maltotriose and melezitose). We benchmarked our results with ion mobility spectrometry and showed a correspondence between the methods to distinguish structural isomers. The ability to spatially resolve isomeric molecules in mixtures and on surfaces using OrbiSIMS can be transformative as these types of molecules play important biological roles.}