An Orbitrap/Time-of-Flight Mass Spectrometer for Photofragment Ion Imaging and High-Resolution Mass Analysis of Native Macromolecular Assemblies

We discuss the design, development, and evaluation ofan Orbitrap/time-of-flight(TOF) mass spectrometry (MS)-based instrument with integrated UV photodissociation(UVPD) and time/mass-to-charge ratio (m/z)-resolved imaging for the comprehensive study of the higher-ordermolecular structure of macromolecular assemblies (MMAs). A bespokeTOF analyzer has been coupled to the higher-energy collisional dissociationcell of an ultrahigh mass range hybrid quadrupole-Orbitrap MS. A 193nm excimer laser was employed to photofragment MMA ions. A combinationof microchannel plates (MCPs)-Timepix (TPX) quad and MCPs-phosphorscreen-TPX3CAM assemblies have been used as axial and orthogonal imagingdetectors, respectively. The instrument can operate in four differentmodes, where the UVPD-generated fragment ions from the native MMAions can be measured with high-mass resolution or imaged in a mass-resolvedmanner to reveal the relative positions of the UVPD fragments postdissociation.This information is intended to be utilized for retrieving higher-ordermolecular structural details that include the conformation, subunitstoichiometry, and molecular interactions as well as to understandthe dissociation dynamics of the MMAs in the gas phase.