Surface-confined ionic liquid (SCIL) stationary phases for high performance liquid chromatography (HPLC) have shown utility in separating various classes of compounds, yet very little work has been completed to provide insights into the retention mechanism of the phases. Previous investigations in our laboratory have shown that the retention characteristics of the SCIL phases can be adequately modeled by the linear solvation energy relationship (LSER) methodology.
This body of work is a continuation of work completed previously in our laboratory and examines synthesis strategies as well as a characterization of SCIL phases by the LSER model. The first Chapter provides a survey of the history of covalently modified silica sorbents and the development of surface-confined ionic liquids for use as stationary phases in HPLC. The utility of SCIL phases reported in literature are highlighted as well as an overview of the methods used in this manuscript (LSER and κ - κ plots) to glean information about the retention mechanisms of stationary phases from chromatographic retention data. A major portion of this final section is devoted to building the statistical model which was used to evaluate the similarities/differences between the LSER system coefficients in the third chapter of this manuscript.
Chapter 2 discusses the synthesis of SCIL stationary phases for HPLC. Details outlining the synthesis, isolation and subsequent grafting of an 8-bromooctyl-1-trichlorosilane linking ligand to a silica surface are discussed. Furthermore, methods for the subsequent attachment of ionic liquid precursor compounds to the previously modified sorbents, forming SCIL stationary phases, are presented. This chapter also includes imaging by scanning electron microscopy and elemental analysis results for the modified sorbents.
In Chapter 3, a statistical model is employed in conjunction with the LSER model to examine the role of the cation and anion on retention of neutral aromatic probe solutes. Similarities/differences in the energetics of retention between the stationary phases were examined by κ-κ plots.
Applications of these novel SCIL phases are discussed in Chapter 4. An excellent correlation was observed between partition coefficients of selected solutes in a biphasic water/ionic liquid system and retention of the solutes on an SCIL phase. Indeed, the SCIL phase may prove to be a viable alternative to the cumbersome and laborious shake flask method. The separation of geometric isomers were also identified as an interesting application of the SCIL phases. Separations of the isomers of nitroaniline, cresol and dichlorobenzene are discussed.
Summaries of the results from the previous chapters are presented in Chapter 5 along with suggested future directions for this project.