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Do we understand the role of mobile phase in separations of polar compounds?

Autoři: Jandera Pavel | Soukup Jan | Janás Petr | Staňková Magda

Rok: 2015

Druh publikace: ostatní - přednáška nebo poster

Strana od-do: nestránkováno

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Jazyk	Název	Abstrakt	Klíčová slova
eng	Do we understand the role of mobile phase in separations of polar compounds?	In the past ten years, LC on polar stationary phases with mobile phases containing organic solvent and less than 5–40% water (HILIC) has become preferred method for separation of polar compounds, namely pharmaceuticals or biopolymers. On polar columns, sample interactions, retention and separation selectivity may strongly change across the full composition range of aqueous-organic mobile phases, HILIC retention mechanism predominating in the organic-rich, and reversed-phase (RP) mechanism in more aqueous media. We determined the accumulation of water from acetonitrile-rich aqueous-organic mobile phases in the water-rich diffuse layer filling the pores of eighteen polar columns, using frontal chromatography combined with Karl Fischer titration. The sorption can be described by Langmuir isotherm and it strongly depends on the type of stationary phase, ranging from less than one monomolecular water layer up to 6 - 10 water layers equivalents. Some water present in polar solvents is accumulated even on non-polar columns. Considering the actual concentration of water in calculations largely improves the accuracy of prediction of gradient elution data in HILIC systems. The dual retention mechanism enables using a single polar column alternatively in the HILIC and RP retention modes of various polar sample compounds such as phenolic acids and flavones. This approach enhances separation selectivity and peak capacity in single- and two- dimensional HPLC.

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