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J Chromatogr A. 2015 May 22;1395:57-64. doi: 10.1016/j.chroma.2015.03.044. Epub 2015 Mar 24.

Contributions to reversed-phase column selectivity: III. Column hydrogen-bond basicity.

Author information

1
University of Minnesota, Minneapolis, MN, USA.
2
LC Resources, Lafayette, CA, USA. Electronic address: John.Dolan@LCResources.com.
3
Florida State University, Tallahassee, FL, USA.
4
LC Resources, Lafayette, CA, USA.
5
Advanced Materials Technologies, Wilmington, DE, USA.

Abstract

Column selectivity in reversed-phase chromatography (RPC) can be described in terms of the hydrophobic-subtraction model, which recognizes five solute-column interactions that together determine solute retention and column selectivity: hydrophobic, steric, hydrogen bonding of an acceptor solute (i.e., a hydrogen-bond base) by a stationary-phase donor group (i.e., a silanol), hydrogen bonding of a donor solute (e.g., a carboxylic acid) by a stationary-phase acceptor group, and ionic. Of these five interactions, hydrogen bonding between donor solutes (acids) and stationary-phase acceptor groups is the least well understood; the present study aims at resolving this uncertainty, so far as possible. Previous work suggests that there are three distinct stationary-phase sites for hydrogen-bond interaction with carboxylic acids, which we will refer to as column basicity I, II, and III. All RPC columns exhibit a selective retention of carboxylic acids (column basicity I) in varying degree. This now appears to involve an interaction of the solute with a pair of vicinal silanols in the stationary phase. For some type-A columns, an additional basic site (column basicity II) is similar to that for column basicity I in primarily affecting the retention of carboxylic acids. The latter site appears to be associated with metal contamination of the silica. Finally, for embedded-polar-group (EPG) columns, the polar group can serve as a proton acceptor (column basicity III) for acids, phenols, and other donor solutes.

KEYWORDS:

Column hydrogen-bond basicity; Column selectivity; HPLC; Hydrophobic–subtraction model; Retention mechanism; Reversed-phase

PMID:
25890437
DOI:
10.1016/j.chroma.2015.03.044
[Indexed for MEDLINE]

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