title: Influence of preferential adsorption of mobile phase on retention  behavior of amino acids on the teicoplanin chiral selector.
abstract: The adsorption behavior of two amino acids, i.e., l,d-threonine and l,d-methionine has been investigated on the chiral stationary phase (CSP)column packed with teicoplanin bonded to a silica support. The study has been performed under non-linear conditions of adsorption isotherm for various types of organic modifiers (methanol, ethanol, propan-2-ol and acetonitrile) in the reversed-phase mode. A heterogeneous adsorption mechanism of amino acids has been identified that was strongly affected by the nature of organic modifier. Generally, isotherm non-linearity and retention decreased with decrease of the modifier content in the mobile phase exhibiting a minimum at water-rich mobile phases. These trends were suggested to result from a combined effect of the mobile as well as the adsorbed phase composition. To determine the composition of the adsorbed phase the excess adsorption of modifiers in aqueous solutions has been measured and their binary adsorption equilibria have been quantified and compared. Strongly non-ideal behavior of solvents in the mobile phase and the adsorbed phase has been accounted for by activity coefficients. The fraction of the modifiers in the adsorbed phase decreased in the sequence: methanol, ethanol, propan-2-ol and acetonitrile.
authors.affiliation: Chemical and Process Engineering Department, Rzeszów University of Technology, Rzeszów, Poland.
authors.forename: Izabela
authors.initials: I
authors.lastname: Poplewskaa
authors.forename: Renata
authors.initials: R
authors.lastname: Kramarz
authors.forename: Wojciech
authors.initials: W
authors.lastname: Piatkowski
authors.forename: Andreas
authors.initials: A
authors.lastname: Seidel-Morgenstern
authors.forename: Dorota
authors.initials: D
authors.lastname: Antos
mesh_terms: D019840:2-Propanol / Q000737:chemistry; D000097:Acetonitriles / Q000737:chemistry; D000327:Adsorption; D000596:Amino Acids / Q000737:chemistry* / Q000302:isolation & purification; D002853:Chromatography, Liquid / Q000379:methods*; D000432:Methanol / Q000737:chemistry; D015394:Molecular Structure; D015203:Reproducibility of Results; D013237:Stereoisomerism; D017334:Teicoplanin / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D000596:Amino Acids; D017334:Teicoplanin; D019840:2-Propanol; D000432:Methanol; C032159:acetonitrile