AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Determination of Gas Phase Ion Structures of Locally Polar Homopolymers through High Resolution Ion Mobility Spectrometry-Mass Spectrometry
CARLOS LARRIBA-ANDALUZ, Xi Chen, IUPUI
Abstract Number: 252 Working Group: Aerosol Physics
Abstract The strong synergy arising from coupling two orthogonal analytical techniques such as ion mobility and mass spectrometry can be used to separate complex mixtures and determine structural information of analytes in the gas phase. A tandem study is performed using two systems with different gases and pressures to ascertain gas phase conformations of homopolymer ions polyethylene-glycol(PEG), polycaprolactone (PCL) and polydimethylsiloxane(PDMS). The studies of these three polymers are made using two very different IMS-MS systems and conditions albeit with the similarity that the mobilities calculated in both systems are directly related to the raw variables used. The first system is an ultra-high resolution (R~150-400) 4m Drift Tube that operates at low pressure and He gas coupled to an in-house MS system. The second system is a high resolution (R~50-60) DMA system that operates at atmospheric pressure in N2 coupled to a commercial triple quadrupole Time of Flight system (ToF). Both systems use similar ESI sources to ionize the same analyte solutions in order to lower the amount of external variables that might affect the gas phase configurations.
Aside from the typical spherical and stretched configurations, intermediate configurations formed by a multiply charged globule and a “bead-on-a-string” appendix are confirmed for all three polymers. These intermediate configurations are shown to be ubiquitous for all charge states and masses present. For each charge state, configurations evolve in two distinctive patterns; an inverse evolution which occurs as an elementary charge attached to the polymer leaves the larger globule and incorporates itself into the appendage, and a forward evolution which reduces the globule without relinquishing a charge while leaving the appendix relatively constant. Forward evolutions are confirmed to form self-similar family shapes that transcend charge states for all polymers. Identical structural changes occur at the same mass over charge regardless of the system, gas or pressure strongly suggesting that conformations are only contingent on number of charges and chain length, and start arranging once the ion is at least partially ejected from the droplet, supporting a charge extrusion mechanism. The high resolution achieved with the drift tube allows many of the transitions to be completely resolved clearly for the first time where charge states “interweave”. These transitions seem to extend to very high charge states and masses (up to the resolving power of the instrument and up to hundreds of kDa) without any observable difference in the family self-similar shapes. As such, the globule plus appendix structures present in PEG are confirmed for the other two polymers. Moreover, the transitions for PCL appear to be analogous to those of PEG while PDMS follows similar trends but with less sharp transitions. This is to be expected due to the increased steric hindrance caused by the methyl pendant groups. This study has implications in the study of the configurational space of more complex homopolymers and heteropolymers and other highly deformable particles.