Retention Mechanism in Reversed-Phase Liquid Chromatography:  A Molecular Perspective

Jake L. Rafferty,† Ling Zhang,† J. Ilja Siepmann,*† and Mark R. Schure‡
Departments of Chemistry and of Chemical Engineering and Material Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, and Theoretical Separation Science Laboratory, Rohm and Haas Company, 727 Norristown Road, P.O. Box 0904, Spring House, Pennsylvania 19477-0904
Anal. Chem., 2007, 79 (17), pp 6551–6558
DOI: 10.1021/ac0705115
Publication Date (Web): August 2, 2007
Copyright © 2007 American Chemical Society
†

 University of Minnesota.

,
*

 To whom correspondence should be addressed. E-mail:  siepmann@ chem.umn.edu.

,
‡

 Rohm and Haas Co.

Abstract

A detailed, molecular-level understanding of the retention mechanism in reversed-phase liquid chromatography (RPLC) has eluded analytical chemists for decades. Through validated, particle-based Monte Carlo simulations of a model RPLC system consisting of dimethyloctadecylsilanes at a coverage of 2.9 μmol/m2 on an explicit silica substrate with unprotected residual silanols in contact with a water/methanol mobile phase, we show that the molecular-level retention processes for nonpolar and polar analytes, such as alkanes and alcohols, are much more complex than what has been previously deduced from thermodynamic and theoretical arguments. In contrast to some previous assumptions, the simulations indicate that both partitioning and adsorption play a key role in the separation process and that the stationary phase in RPLC behaves substantially different from a bulk hydrocarbon phase. The retention of nonpolar methylene segments is dominated by lipophilic interactions with the retentive phase, while solvophilic interactions are more important for the retention of the polar hydroxyl group.

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History

  • Published In Issue September 01, 2007
  • Received for review March 12, 2007. Accepted June 1, 2007.

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