Over the past several years, considerable interest has been generated with regard to new approaches to achieve enhanced selectivity in the high performance liquid chromatographic separation of complex mixtures of polar and non-polar compounds. Although reversed phase HPLC still remains the workhorse in many applications, increasingly stationary phases based on other modalities, such as mixed mode (MM), hydrophilic interaction/aqueous normal phase (HILIC/ANP) and stimuli-responsive phenonomena, are finding their way into the tool box of analytical chemists. In order for the full potential of these new types of adsorbents to be captured, the origins of the selectivity characteristics of these types of stationary phases need to be elucidated at multiple levels -- from the hierachial perspectives of a macroscopic separation system, a microscopic separation surface and an atomistic separation structure. In this study, we have examined how different types of surface modified silica-based stationary phases are able to manifest dual modes of selectivity with polar and non-polar compounds through the interplay of reversed phase and aqueous normal phase interactions. In particular, a combination of resolution mapping methods, eluent and solvational energy optimisation procedures, surface characterisation, zeta potential measurements and chemical modification techniques with have been employed to evaluate the origins of the selectivities of different silica-based HILIC/ANP stationary phases, including the Diamond HydrideTM phase and other silica hydride derived adsorbents[1,2,3] with the emphasis of these studies focused on the analysis of polar molecules present in complex mixtures derived from biologically and synthetic sources.

[1] Boysen, R.I., Yang, Y., Chowdhury, J., Matyska, M.T., Pesek, J.J. and Hearn, M.T.W. J. Chromatogr. A, 1218, (2011) 8021-8026.
[2] Pesek, J.J., Matyska, M.T., Boysen, R.I., Yang, Y. and Hearn, M.T.W. TrAC 42 (2013) 64-73.
[3] Yang, Y., Boysen, R.I., Kulsing, C., Matyska, M.T., Pesek, J.J. and Hearn, M.T.W., J. Sep. Sci., (2013) in press