title: Contributions to reversed-phase column selectivity: III. Column hydrogen-bond basicity.
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.
authors.affiliation: University of Minnesota, Minneapolis, MN, USA.
authors.forename: P W
authors.initials: PW
authors.lastname: Carr
authors.affiliation: LC Resources, Lafayette, CA, USA. Electronic address: John.Dolan@LCResources.com.
authors.forename: J W
authors.initials: JW
authors.lastname: Dolan
authors.affiliation: Florida State University, Tallahassee, FL, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Dorsey
authors.affiliation: LC Resources, Lafayette, CA, USA.
authors.forename: L R
authors.initials: LR
authors.lastname: Snyder
authors.affiliation: Advanced Materials Technologies, Wilmington, DE, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Kirkland
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry; D056148:Chromatography, Reverse-Phase / Q000379:methods* / Q000592:standards*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008670:Metals / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D002264:Carboxylic Acids; D008670:Metals; D012822:Silicon Dioxide
keywords: Column hydrogen-bond basicity; Column selectivity; HPLC; Hydrophobic–subtraction model; Retention mechanism; Reversed-phase