Simultaneous Fragmentation of Multiple Ions Using IMS Drift Time Dependent Collision Energies

Ion mobility spectrometry coupled with mass spectrometry (IMS-MS) was utilized to evaluate an ion collision energy ramping technique that simultaneously fragments a variety of species. 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 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 octopole in the mass spectrometer. To explore the fragmentation spectrum of each precursor ion, the bias voltages for the short quadrupoles and conductance limiting orifices were increased from 0 to 50 V above nonfragmentation voltage settings. An approximately linear correlation was observed between the optimal fragmentation voltage for each ion and its 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 state ions) and more to low mobility ions. Fragmentation efficiencies were found to be similar for different ions when the fragmentation voltage was linearly ramped with drift time, but varied drastically when only a single voltage was used.