PNNL

Abstract

Ion mobility spectrometry coupled with mass spectrometry (IMS-MS) was utilized to evaluate an ion collision energy ramping technique for simultaneously fragmenting all ions in a mixture without causing over- or under-fragmentation. To evaluate this technique, the fragmentation patterns of a mixture of ions ranging in mass, charge state and drift time were analyzed to determine their optimal fragmentation conditions. The precursor ions were pulsed into the IMS-MS instrument and separated in the IMS drift cell based on mobility differences. Two differentially pumped short quadrupoles were used to focus the ions exiting the IMS drift cell, and fragmentation was induced by collision induced dissociation (CID) between the conductance limiting orifice behind the second short quadrupole and before the first MS octopole. To explore the fragmentation spectrum of each precursor ion, the bias voltages for the short quadrupoles and the conductance limiting orifices were all increased from 0 V to 50 V above the non-fragmentation voltage settings. A linear correlation was observed between the optimal fragmentation voltage for each ion and their specific drift time, so a linear voltage gradient was employed to supply less collision energy to high mobility ions (e.g., small conformations or higher charge states) and more to low mobility ions. Fragmentation efficiencies were calculated for all ions, and similar values were observed when the fragmentation voltage was linearly ramped with IMS drift time, but varied drastically when only a single fragmentation voltage was used.