title: Sorption of the organic cation metoprolol on silica gel from its aqueous solution considering the competition of inorganic cations.
abstract: Systematic batch experiments with the organic monovalent cation metoprolol as sorbate and the synthetic material silica gel as sorbent were conducted with the aim of characterizing the sorption of organic cations onto charged surfaces. Sorption isotherms for metoprolol (>99% protonated in the tested pH of around 6) in competition with mono- and divalent inorganic cations (Na(+), NH4(+), Ca(2+), and Mg(2+)) were determined in order to assess their influence on cation exchange processes and to identify the role of further sorptive interactions. The obtained sorption isotherms could be described well by an exponential function (Freundlich isotherm model) with consistent exponents (about 0.8). In general, a decreasing sorption of metoprolol with increasing concentrations in inorganic cations was observed. Competing ions of the same valence showed similar effects. A significant sorption affinity of metoprolol with ion type dependent Freundlich coefficients KF,0.77 between 234.42 and 426.58 (L/kg)(0.77) could still be observed even at very high concentrations of competing inorganic cations. Additional column experiments confirm this behavior, which suggests the existence of further relevant interactions beside cation exchange. In subsequent batch experiments, the influence of mixtures with more than one competing ion and the effect of a reduced negative surface charge at a pH below the point of zero charge (pHPZC ≈ 2.5) were also investigated. Finally, the study demonstrates that cation exchange is the most relevant but not the sole mechanism for the sorption of metoprolol on silica gel.
authors.affiliation: Institute of Water Chemistry, Technische Universität Dresden, 01062 Dresden, Germany(1). Electronic address: Susann.Kutzner@mailbox.tu-dresden.de.
authors.forename: Susann
authors.initials: S
authors.lastname: Kutzner
authors.affiliation: Geoscience Centre, Department of Applied Geology, University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany(2).
authors.forename: Mario
authors.initials: M
authors.lastname: Schaffer
authors.affiliation: Institute of Water Chemistry, Technische Universität Dresden, 01062 Dresden, Germany(1).
authors.forename: Hilmar
authors.initials: H
authors.lastname: Börnick
authors.affiliation: Geoscience Centre, Department of Applied Geology, University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany(2).
authors.forename: Tobias
authors.initials: T
authors.lastname: Licha
authors.affiliation: Institute of Water Chemistry, Technische Universität Dresden, 01062 Dresden, Germany(1).
authors.forename: Eckhard
authors.initials: E
authors.lastname: Worch
mesh_terms: D000327:Adsorption; D061249:Batch Cell Culture Techniques; D002412:Cations; D006863:Hydrogen-Ion Concentration; D007287:Inorganic Chemicals / Q000737:chemistry*; D016014:Linear Models; D008790:Metoprolol / Q000737:chemistry / Q000302:isolation & purification*; D008962:Models, Theoretical; D012044:Regression Analysis; D058428:Silica Gel / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D002412:Cations; D007287:Inorganic Chemicals; D012996:Solutions; D014867:Water; D058428:Silica Gel; D008790:Metoprolol
keywords: Competitive sorption; Freundlich isotherm; Ion exchange; Metoprolol; Organic cation; Silica gel