A high resolution atmospheric pressure matrix-assisted laser desorption/ionization-quadrupole-orbitrap MS platform enables in situ analysis of biomolecules by multi-mode ionization and acquisition.

Introduced in 2000, atmospheric pressure (AP)/matrix-assisted laser desorption/ionization (MALDI) has attracted substantial attention in the mass spectrometry community due to its ease of sample introduction and handling, interchangeability with ESI source and capability of analyzing volatile species. In this study, an AP/MALDI source with ultra-high spatial resolution was coupled to a Q Exactive HF orbitrap mass spectrometer for high resolution in situ analysis by MALDI, laserspray ionization (LSI) and matrix assisted ionization (MAI) without instrument modification. LSI and MAI generated multiply charged ions, which expanded the mass detection range and improved fragmentation efficiency. Full MS, targeted MS/MS, data dependent acquisition (DDA) and parallel reaction monitoring (PRM) acquisitions were performed on peptide and protein standards, tissue extracts and tissue sections for in depth characterization of various biomolecules. High resolution full MS and MS/MS images were obtained from crustacean and rat tissues with pixel size less than 30 μm. Overall, AP/MALDI-Q-Orbitrap is a fast scanning instrument that is capable of performing multiple types of ionization and multiple acquisition modes without instrument modification. This instrument platform provides an attractive alternative to other high resolution MALDI instruments.