DEVELOPMENT OF A 3D ION TRAP FOR ION/ION REACTIONS AND MASS ANALYSIS INVOLVING HIGH MASS BIOMOLECULAR IONS
Advances in mass spectrometry (MS) instrumentation and techniques have provided approaches for complementing current biochemical research. Native mass spectrometry, which aims to analyze intact biomolecules and biomolecular complexes, has become a powerful tool for identifying and measuring different units of complex structures as well as probing interactions among the different units. Ion traps generally are important in native MS workflows because of their ability to accumulate ions and perform multi-stage analyses including fragmentation, photoreactions, and gas-phase reactions with reagent molecules or ions. Native MS, however, has shortcomings primarily due to the preferred ionization technique, electrospray ionization (ESI). ESI tends to distribute signal from a single analyte among a range of charge states. Additionally, the ions generated from droplets tend to carry adducted molecules and ions proportional to the size of the analyte. For analysis of high mass and heterogeneous biomolecular complexes, these shortcomings lead to wide overlapping charge states for different components that might be difficult to interpret correctly. Charge reduction via gas-phase ion/ion reactions facilitates interpretation of native mass spectra by generating product ions that are well separated in m/z. Current sine wave technology limits the upper m/z range of ion traps required for stabilizing and measuring high mass ion/ion reaction products. Digital ion trapping (DIT) technology circumvents the voltage limitations of sine wave technology by varying frequency to achieve high m/z. The combination of ion/ion reactions and DIT operation facilitates further unique probing reactions such as fragmentation reactions of charge reduced biomolecular complexes via neutral collisions and photoreactions. DIT operation also provides a straightforward approach for isolation of high m/z ions using duty cycle modulation to further facilitate analysis of heterogeneous mixtures. This work highlights developments of a home-built 3D ion trap mass spectrometer as a viable native MS platform.