Eliza Łata, Agnieszka Fulczyk, Mieczysław Sajewicz, Teresa Kowalska
Institute of Chemistry, University of Silesia, 9 Szkolna Street, 40-006 Katowice, Poland
This email address is being protected from spambots. You need JavaScript enabled to view it.
Effective diffusion is one of these phenomena which on an everyday basis take place in chromatographic systems, yet usually tend to be overlooked in an everyday analytical practice. Unlike in the column chromatography, in planar chromatography effective diffusion is two-dimensional [1].
On some rare occasions, horizontal direction of effective diffusion can proof beneficial. It happens, when certain compounds of a very similar chemical structure (and/or molecular weight) cannot be separated vertically without applying special separation conditions. So far, however, an exact physicochemical mechanism of horizontal separations remains rather obscure. It can only be assumed that the chirality of silica gel (as confirmed by the circular dichroism (CD) spectroscopy [2]) is one reason of horizontal separations. In combination with horizontal effective diffusion, it can result in spectacular yet rare horizontal separations. Moreover, it was documented upon numerous examples that horizontal separations in the TLC/HPTLC systems most likely occur with the rod-shaped molecules additionally equipped with asymmetry centers [3] and with the pairs of enantiomers [4]. The mechanism of such separations can be by the auto-driven propeller-like motions of the analytes themselves, the Magnus forces-induced motion, or by still another yet unknown mechanism [3].
In this talk, a very spectacular example of horizontal separation is presented of the rod-shaped red betacyanin pigments equipped with asymmetry centers, which are derived from the red beet (Beta vulgaris L.) juice [5].
References
[1] T. Kowalska, K. Kaczmarski, W. Prus, Theory and mechanism of thin-layer chromatography. In: J. Sherma and B. Fried (Eds.), Handbook of Thin-Layer Chromatography, 3rd Ed. Revised and Expanded, Marcel Dekker, New York, 2003; pp. 47-80.
[2] M. Sajewicz, H.-E. Hauck, G. Drabik, E. Namysło, B. Głód, T. Kowalska, J. Planar Chromatogr. 19 (2006) 278-281.
[3] J. Polanski, M. Sajewicz, M. Knas, A. Zywocinski, M. Weloe, T. Kowalska, Chemistry Today, Monographic Supplement “Chiral Technologies” 30 (2012) 18-21.
[4] M. Sajewicz, R. Piętka, A. Pieniak, T. Kowalska, Acta Chromatogr. 15 (2005) 131-149.
[5] E. Łata, A. Fulczyk, T. Kowalska, M. Sajewicz, J. Chromatogr. Sci. 58 (2020) 5-15.
