Soft ionization methods (such as ESI, MALDI, DESI, APCI, APPI, etc.) generate ions through gentle charge transfer or photochemical processes, mostly keeping the molecular structure intact, with spectra dominated by quasi-molecular ion peaks, suitable for what-molecule imaging-based identification.
Hard ionization (typically EI electron impact) uses high-energy electrons to fragment molecules, producing characteristic fragment spectra; the spectra are complex but have a molecular fingerprint, commonly used for structure identification by comparison with standard spectral libraries, yet difficult to directly give intact molecular ions.
Imaging mass spectrometry mostly uses soft ionization, because it needs to directly localize intact molecules (lipids, peptides, metabolites, drugs) on tissue sections; retaining quasi-molecular ions enables the mapping from m/z to molecular species. MALDI, DESI, and LDPI all belong to the soft ionization route.
Hard ionization is rarely used as the main imaging mode in imaging, but when structural confirmation is needed (such as distinguishing isomers and identifying unknown metabolites), it can be combined with tandem mass spectrometry (MS/MS) or off-axis fragment analysis to supplement information, rather than replacing soft ionization imaging itself.
Even with soft ionization, tandem mass spectrometry is often used to actively induce fragmentation for structural clues - equivalent to introducing a controlled hard step on demand on top of soft ionization fidelity. Therefore modern imaging is often a combination of soft-ionization acquisition plus on-demand MS/MS verification.
This combination balances molecular localization and structural credibility: first draw the spatial distribution with soft ionization, then perform fragment identification on pixels of interest, avoiding molecular information loss caused by a single hard-ionization imaging.
If the goal is direct imaging localization of known or candidate molecules, prioritize soft ionization sources (MALDI, DESI, LDPI, etc.); if the core is unknown structure identification, hard ionization or MS/MS capability is needed. Most spatial metabolomics work uses soft ionization as primary and MS/MS as auxiliary.
For applications requiring matrix-free, ambient, in-situ conditions, soft-ionization sources such as LDPI/DPI are more suitable; for GC-MS-style standard spectral library searching, hard ionization such as EI remains irreplaceable.
To obtain detailed specifications, compatible models, or a quotation for the MSI LDPI / DPI full series imaging ion sources, visit the Neo-Source official website, or contact the official team for compatibility advice tailored to your mass spectrometer (Agilent / SCIEX / Thermo and other mainstream MS).