title: Ultra-thin porous glass membranes--an innovative material for the immobilization of active species for optical chemosensors.
abstract: In addition to polymers, porous glasses can be used for the immobilization of indicators, chromoionophores or enzymes. Advantages of these materials include, among others, the photochemical and thermal stability. Porous glass membranes (CPG) based on phase-separated alkali borosilicate glasses with thicknesses of 250-300 μm and dimensions of approximately 9-13 mm² were used in this work. The average pore diameter was found to be between 12 and 112 nm. Initially, the membrane permeability for water was determined. Furthermore, the absorption spectra for the water-soaked membranes were recorded optically. CPG membranes which are pH-sensitive were prepared based on the covalent immobilization of thymol blue and a derivative of styryl acridine. In each case, the absorption spectra of the immobilized indicators are shown. The t90-times vary between 4 and 20 min and were determined for the thermodynamic equilibrium. The influence of the ionic strength on the characteristic curve is discussed and detailed results are given. After the storage time of about 900 days a pH-sensitivity for a CPG membrane styryl acridine derivative sample was still detectable.
authors.affiliation: CiS Forschungsinstitut für Mikrosensorik und Photovoltaik GmbH, Konrad-Zuse-Straße 14, 99099 Erfurt, Germany. rmueller@cismst.de
authors.forename: R
authors.initials: R
authors.lastname: Müller
authors.forename: N
authors.initials: N
authors.lastname: Anders
authors.forename: J
authors.initials: J
authors.lastname: Titus
authors.forename: D
authors.initials: D
authors.lastname: Enke
mesh_terms: D000166:Acridines / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D010539:Permeability; D016062:Porosity; D017640:Silicates / Q000737:chemistry; D013053:Spectrophotometry; D013944:Thymolphthalein / Q000031:analogs & derivatives* / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D000166:Acridines; D004396:Coloring Agents; D008567:Membranes, Artificial; D017640:Silicates; D014867:Water; C013713:thymol blue; D013944:Thymolphthalein