desorptionionization

Desorption ionization is a class of ionization methods used in mass spectrometry in which analyte molecules are released from a solid or surface (desorption) and converted into charged particles (ionized) in a single step. This approach enables the analysis of materials directly from surfaces with minimal or no elaborate sample preparation and is widely used for surface analysis and imaging.

Common desorption ionization techniques include MALDI, DESI, DART, and SIMS. MALDI uses a UV laser and a matrix to absorb energy and assist desorption and ionization of the embedded analyte. DESI directs a spray of charged solvent droplets onto a surface, causing the analyte to dissolve and ionize upon impact. SIMS bombards the surface with high-energy ions, ejecting and ionizing surface species, often with significant fragmentation. DART uses a heated gas or plasma to desorb molecules that are then ionized by atmospheric ions. Each method operates under different conditions and is suitable for different classes of compounds and surfaces.

Applications include proteomics, lipidomics, metabolomics, imaging of tissue sections, analysis of pharmaceuticals and polymers, forensic analysis, and materials science. DESI and MALDI imaging, in particular, map the spatial distribution of molecules across a surface.

Advantages of desorption ionization methods include minimal sample preparation, ambient operating conditions (for several techniques), high sensitivity for certain analytes, compatibility with solids and delicate surfaces, and the ability to obtain spatial information through imaging. Limitations can include matrix effects and ion suppression, variable spatial resolution, fragmentation (notably in SIMS), and equipment complexity and cost, which can influence suitability for a given application.