Researchers at the UK’s National Physical Laboratory and their collaborators showed that Orbitrap-SIMS can identify and map similar-looking molecules directly on surfaces without extra sample preparation.
The problem is that molecules with the same chemical formula and mass but different arrangements of atoms, called structural isomers, can look identical in standard imaging that relies on mass. The team used Orbitrap secondary ion mass spectrometry (OrbiSIMS). Researchers adjusted how ions made from a sample break apart and move through gas inside the instrument, revealing differences linked to molecular structure.
The researchers tested the method on three sugars that are structural isomers: raffinose, maltotriose and melezitose. They also mapped where raffinose and maltotriose were in mixtures. They reported that the resulting patterns agreed with comparisons made using ion mobility spectrometry.
The work was published in Nature Communications on October 17. It could help researchers study where distinct sugars and other isomers occur in complex samples. The demonstration focused on the three test sugars.
Applying the method to other molecules and biological materials will require further investigation.