Infrared Matrix-Assisted Laser Desorption Electrospray Ionization Mass Spectrometry Imaging (IR-MALDESI MSI): Fundamentals, Source Design and Data Analysis

Matrix-Assisted Laser Desorption Electrospray Ionization (MALDESI) was the first hybrid ionization source combining laser ablation and electrospray post-ionization using a resonantly excited matrix (endogenous or exogenous) to enhance the desorption of neutral analyte molecules. In infrared(IR)-MALDESI, exogenous water in the form of ice can be used as a matrix to improve the desorption of neutrals by matching the excitation laser wavelength with the O-H stretching modes (2.94 microm). IR-MALDESI is also an ambient pressure ionization source, meaning that ions are formed outside of the mass spectrometer instrument and that interrogation can be performed with minimal or no sample preparation. The technique combines characteristics of ESI such as the capability to generate multiply charged ions as well as features of MALDI such as high resistance to salts and the capability to spatially resolve sample collection over a surface. The latter characteristic enabled the development of an automated, high throughput IR-MALDESI mass spectrometry imaging (MSI) source. The engineered device was coupled to a high mass resolving power LTQ-FT-ICR instrument and offered multi-shot capability with full control over the repetition rate and the scanning cycle. It was also demonstrated that that a spatial resolution of 45 mm can be achieved in oversampling mode.;A novel flash shadowgraphy system which has the capability to simultaneously collect images of the plume of ablated material and record the IR-MALDESI mass spectrum associated with that same plume was implemented. The system was used to investigate the fundamentals of the IR-MALDESI ablation/ionization process and optimize the source for the imaging of biological tissues using ice as a matrix by nearly ten folds.;High throughput MSI using high resolving power instruments generate extremely large sets of data. MSiReader, a vendor neutral interface was developed to view and process this imaging data. MSiReader is fully customizable and several features were implemented such as automatic peak detection, image colocalization, data extraction, customizable centroid calculation, data normalization and image batch processing. The user friendly interface is compatible with most of the vendor neutral MSI data file formats and has been released to the MS community as a free, open source software tool.