Date of Award

Spring 4-25-2023

Degree Type

Dissertation

Degree Name

PhD. Chemistry

Department

Chemistry and Biochemistry

Advisor

Yuri V. Kazakevich, Ph.D.

Committee Member

Nicholas H. Snow, Ph.D.

Committee Member

Alexander Y. Fadeev, Ph.D.

Keywords

Surface, Mixed-Mode, Chromatography, HPLC, BET, C-Constant

Abstract

Mixed-mode chromatography is a chromatographic method in which solutes interact with stationary phase through more than one interaction mode or mechanism. It is because of these multiple complex interactions, which makes it difficult to predict chromatographic behavior of analytes on Mixed-mode columns. In order to fully understand the retention mechanisms on Mixed-mode columns, the packing material properties must be well characterized since each characteristic may contribute to the overall chromatographic performance of the column. Many non-chromatographic and chromatographic techniques are available to characterize and compare Mixed-mode columns in terms of their interaction abilities, retentivity, surface chemistry, chemical properties and geometry. Characterization of different Mixed-mode columns on the basis of interaction energy characteristics has not been explored.

In this study, different ratios of porous silica (Axia Luna Silica) and C18 (Axia Luna C18), which are commonly used single mode adsorbents were blended in various ratios to simulate Mixed-mode materials and analyzed by Low Temperature Nitrogen Adsorption (LTNA). Adsorption isotherms, surface area, and BET C-Constants were obtained for all the blended materials and a linear relationship between the BET C-Constant and the blend ratio of silica has been observed. A new BET C-Constant energy scale was created from a plot of non-specified average interaction energy vs. percent silica surface.

A variety of commercially available Mixed-mode columns were unpacked and the materials were analyzed by LTNA in order to explore the use of the BET C-Constant energy scale as a universal indexation system to characterize Mixed-mode materials. Adsorption isotherms, surface area, and BET C-Constants were obtained for all the commercial Mixed-mode materials. The non-specified average interaction energy and the equivalent percent silica surface was calculated from the BET C-Constant and plotted on the BET C-Constant energy scale to enable Mixed-mode column comparison based on average interaction energy. The data in this research project suggests that the BET C-Constant may be a viable parameter that can be used to characterize commercial Mixed-mode columns on the basis of average interaction energy.

Utilizing this BET C-Constant energy scale in conjunction with the study of retention behaviors on Mixed-mode material could lead to improvements in the understanding of method development on Mixed-mode columns, allow the comparison and selection of commercialized Mixed-mode columns, and even predict retention behavior of analytes in Mixed-mode columns.

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