title: Effect of carbon loading on the extraction properties of C-18 bonded silica used for solid-phase extraction of acidic and basic analytes.
abstract: A range of C-18 bonded phases for solid-phase extraction (SPE), with different carbon loadings and degrees of end capping, have been evaluated for the extraction of model acidic and basic analytes (anisic acid and propranolol, respectively). High carbon loadings (18 and 22%) were associated with poor extraction properties with losses on application and wash steps. Recovery of extracted analytes from such materials was also inefficient, suggesting poor mass transfer properties. A low-carbon-loaded phase (5%), though capable of efficient extraction of the analytes, was seen to be poorly retentive. The best SPE phases for either analyte were those of intermediate carbon loading (∼15%). Significant effects of end capping were only observed for the basic analyte propranolol, where retention was probably mediated by silanophilic interactions.
authors.affiliation: Department of Safety of Medicines, Zeneca Pharmaceuticals, Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG, U.K., and Department of Chemistry, University of Keele, Staffordshire ST5 5BG, U.K.
authors.forename: P
authors.initials: P
authors.lastname: Martin
authors.forename: E D
authors.initials: ED
authors.lastname: Morgan
authors.forename: I D
authors.initials: ID
authors.lastname: Wilson