Organic molecule analysis using surplus expansion type Kendrick Mass Defect (KMD) analysis

Abstract

Mass spectrometry enables highly sensitive detection of biomolecules and is widely used in imaging analysis to visualize the spatial distribution of molecules within tissues. The presence of fragment ions, which are generated when molecules break apart during ionization, can complicate spectral interpretation. Organic molecules with hydrocarbon chains, such as lipids, often produce fragment ions differing by CH₂ units. The Kendrick Mass Defect (KMD) method classifies ions with common functional groups based on shared KMD values. Conventional KMD methods, however, make it difficult to compare KMD values and distinguish between different functional groups. In this study, we introduce an improved approach that utilizes the remainder of m/z divided by CH₂ units, enabling easier comparison of functional group differences and structural variations. This method is broadly applicable not only to lipids but also to organic molecules with specific repeating structures.