Towards higher resolution in ion mobility spectrometry and an advanced understanding of polyubiquitins

Ion mobility spectrometry (IMS) when coupled to mass spectrometry (MS) has enabled a wide range of advances in structural analysis and the separation of complex mixtures. Over the last fifteen years many advances have been made in the sensitivity of such hybrid instruments. Fewer advances have been made in the resolving power of IMS instruments such that in many experiments today, resolving power is the bottleneck towards a greater understanding of structure. Recently a circular drift tube has been constructed to reach increased resolving powers but it operates in an overtone mobility spectrometry (OMS)-like mode that requires scanning a frequency to obtain different mobilities, drastically reducing throughput. In these studies, a theoretical treatment is developed to explain the maximum overtones observed in OMS. From this theory a method of asymmetric pulsing of the phases of OMS to select desired overtones is then derived. The combination of these two theories enhances the use of higher overtones for separations with minimal ambiguity due to overlap of nearby overtones. Using the recently developed gridless OMS technology a new circular drift tube is attached to a linear drift tube with an interface region and alignment such that ions can be rapidly analyzed by nested IMS-MS for a complete spectrum and then select peaks can be targeted by high resolution circular measurements in a mode we denote zoom mode IMS. Proof-of-concept experiments are performed with a simple interface consisting of four lenses surrounding the interface and the applied potentials that direct ions as desired. The majority of the work presented involves the development of theory and instrumentation to improve resolving power in IMS. Also presented herein are experiments that continue a longstanding exploration of the structure of ubiquitin by investigating tetraubiquitin by IMS.