Abstract by Brigham Pope
Chemistry and Biochemistry
MultiCRAFTI: Overcoming Kinetic Energy Dependence and Limits of Fourier Transform Based Single Collision Cross Section Measurements
Cross-sectional areas by FTICR (CRAFTI) provides a complementary technique to ion mobility spectroscopy for ascertaining tertiary molecular structure and shape. Like IMS, CRAFTI gives cross-section measurements that agree with computed values. Unlike IMS, CRAFTI can be performed on any Fourier transform based mass analyzer. CRAFTI depends on single-collision dephasing, which enables CRAFTI to characterize structures that are too fragile to survive the multiple-collision conditions of IMS. However, the single-collision assumption fails when more massive ions cannot reach sufficient kinetic energies for single-collision dissociation and therefore require multiple collisions, resulting in artificially small cross-sections. By performing CRAFTI on tetraalkylammoniums over a wide range of kinetic energies, we show that cross-section consistently increases with energy and plateaus at the correct cross-section at 50 eV, making our mass limit 730 m/z. MultiCRAFTI, which is acquiring relative cross-sections by measuring two ions at the same kinetic energy gives correct cross-sections at energies as low as 13 eV, extending our limit to over 1450 m/z.