Development and Characterization of an Atmospheric Pressure Ionization Source Matrix-Assisted Laser Desorption Electrospray Ionization Coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Analysis of Biological Macromolecules

Abstract

The field of mass spectrometry has grown tremendously over the past few decades due in large part to the continued application to new and interesting areas of exploration. The advent of soft ionization sources such as electrospray ionization and matrix-assisted laser desorption/ionization have dramatically increased the capabilities of mass spectrometry and increased the amount of information derived from biological samples. As a result, there has been tremendous growth in the development of new ionization source technology in recent years. One of the main driving forces behind the development of new ionization technology is for the reduction of sample preparation required prior to analysis, yielding high throughput sample analysis. Demonstrated herein is the development and characterization of an atmospheric pressure ionization source called matrix-assisted laser desorption electrospray ionization (MALDESI). MALDESI is a hybrid combination of MALDI and ESI which utilizes laser desorption with electrospray postionization for the generation of multiply-charged ions. Multiply-charged ions are of particular importance when using Fourier transform mass spectrometry, due to the increase in resolving power and mass accuracy with increasing charge on the molecule. Top-down characterization of intact polypeptides is demonstrated as well as high mass accuracy utilizing internal calibration. A newly designed highly robust and versatile atmospheric pressure ionization platform is developed and described in detail. Solid- and liquid state analysis of three out of the four classes of biological molecules is demonstrated utilizing the newly developed versatile ionization platform. MALDESI utilizing ultraviolet and infrared laser desorption is demonstrated at various wavelengths (UV, 337 nm and 349 nm and IR, 2.94 µm and 10.6 µm) with and without ESI postionization for the generation of multiply-charged ions. The characteristics of liquid-state samples are described as a macroscopic electrospray droplet and characterized. MALDESI direct analysis is demonstrated and applications for high throughput analysis of complex samples are described.