TAILORED ION CLUSTERING TO AUGMENT GAS-PHASE SEPARATION FACTORS

Pearl Kwantwi-Barima

Ion mobility spectrometry (IMS), though a relatively low-resolution separation method, is a highly sensitive, rapid technique frequently employed in security-related field applications. Given its wide utility, there is a pressing need to enhance IMS separation capacity, which can aid in minimizing false positives and negatives. In select cases, ions with distinct chemical structures will exhibit the same nominal mobility coefficients and remain unresolved using the traditional approach to IMS experimentation. To address these real, and commonly observed occurrences, alternative means of separation is necessary. The use of drift gas modifiers is an alternative way of improving selectivity by fundamentally disrupting the standard ion-neutral interactions and augment selectivity factors in IMS. By combining experimental data with computational modeling, the outlined work in this dissertation describes a fundamentally new approach to quantitatively account for ion-neutral clustering and establish the foundations for a predictive capacity that allows for a considerable improvement ion mobility performance. In the first experimental effort using a set of chemical warfare agent simulants (a mixture of dimethyl methyl phosphonate and methyl phosphonic acid) with nominally the same reduced mobility values as a test case, the new quantitative clustering model agree with the data to a high level of statistical confidence and aid in the understanding of the ion-vapor clustering to realize baseline separation of the target analytes. Building upon the initial quantitative assessment of separations, the original analytical benefits of altering the IMS experiment were expanded to include a homologous series of phosphonic acids. These analytes provided a foundation to probe hypotheses related to the functional group dependence on the chemical ion-vapor clustering model. In addition, amino acids were included in this dissertation work as a test case for future biological samples and different modifiers were tested. Furthermore, the projects completed in this dissertation were not only focused on drift gas modifiers. Additional experiments dedicated to increasing ion throughput using multiplexing techniques such as frequency modulated ion gating coupled with two different types of ion shutter designs (tri-state ion shutter (3S-IS) and two-state ion shutter (2S-IS)) were conducted.

TAILORED ION CLUSTERING TO AUGMENT GAS-PHASE SEPARATION FACTORS

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