The analyte is first vaporized by heating, then enters a reagent gas cloud continuously ionized by corona discharge; reagent ions (such as H3O+) ionize the gas-phase analyte through proton transfer or charge exchange. Because this occurs in the gas phase, the sample must be vaporizable and thermally stable.
Since the ionization target is already-vaporized molecules, APCI is weak for non-vaporizable or heat-sensitive large molecules (proteins, peptides), mainly serving small molecules and moderately polar compounds.
APCI, ESI, and APPI are all ambient soft-ionization methods but differ in mechanism: ESI directly nebulizes charged liquid phase, APCI vaporizes first then chemically ionizes, and APPI uses UV photons for photoionization. For molecules that are hard to electrospray but vaporizable, APCI is often more stable than ESI.
In an imaging context, APCI is mostly used for offline analysis coupled with chromatography rather than directly imaging tissue surfaces point by point like DESI or LDPI; it is a molecular-identification source rather than a primary in-situ imaging source.
APCI performs well for mid-to-low polarity, thermally stable compounds such as pesticides, small drug molecules, lipids, and steroids, and is a mature choice for LC-MS quantitative analysis. Its gas-phase ionization reduces matrix effects and is more robust for complex extracts.
In spatial-analysis workflows, APCI can pair with tissue extraction or micro-sampling to provide high-sensitivity quantitative confirmation of molecules discovered by imaging, rather than replacing in-situ imaging sources.
The limitation is the need for vaporization and thermal stability, which makes it unsuitable for large and heat-sensitive molecules; it is also offline/chromatography-coupled and provides no spatial coordinates. For direct in-situ imaging, imaging sources such as DESI, LDPI, DPI, and MALDI should be prioritized.
Selection advice: choose APCI primarily for small-molecule quantification and LC-MS; choose imaging sources for tissue in-situ molecular distribution, and use APCI/LC-MS for downstream quantitative verification.
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).