title: Time-resolved imaging of the MALDI linear-TOF ion cloud: direct visualization and exploitation of ion optical phenomena using a position- and time-sensitive detector.
abstract: In this study, we describe the implementation of a position- and time-sensitive detection system (Timepix detector) to directly visualize the spatial distributions of the matrix-assisted laser desorption ionization ion cloud in a linear-time-of-flight (MALDI linear-ToF) as it is projected onto the detector surface. These time-resolved images allow direct visualization of m/z-dependent ion focusing effects that occur within the ion source of the instrument. The influence of key parameters, namely extraction voltage (E(V)), pulsed-ion extraction (PIE) delay, and even the matrix-dependent initial ion velocity was investigated and were found to alter the focusing properties of the ion-optical system. Under certain conditions where the spatial focal plane coincides with the detector plane, so-called x-y space focusing could be observed (i.e., the focusing of the ion cloud to a small, well-defined spot on the detector). Such conditions allow for the stigmatic ion imaging of intact proteins for the first time on a commercial linear ToF-MS system. In combination with the ion-optical magnification of the system (~100×), a spatial resolving power of 11–16 μm with a pixel size of 550 nm was recorded within a laser spot diameter of ~125 μm. This study demonstrates both the diagnostic and analytical advantages offered by the Timepix detector in ToF-MS.
authors.forename: Shane R
authors.initials: SR
authors.lastname: Ellis
authors.forename: Jens
authors.initials: J
authors.lastname: Soltwisch
authors.forename: Ron M A
authors.initials: RM
authors.lastname: Heeren
mesh_terms: D053000:Analytic Sample Preparation Methods; D000818:Animals; D055664:Electrochemical Techniques / Q000295:instrumentation; D006041:Goats; D007074:Immunoglobulin G / Q000032:analysis* / Q000737:chemistry; D007202:Indicators and Reagents / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D064847:Multimodal Imaging / Q000295:instrumentation; D055620:Optical Phenomena; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation; D014835:Volatilization
chemical_list: D007074:Immunoglobulin G; D007202:Indicators and Reagents