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Der effektive Diffusionskoeffizient Deff von Gasen in einem porösen Medium hängt im Knudsen- bzw. Übergangsgebiet vom effektiven Porenradius 〈r〉 der Struktur ab. 〈r〉 kann aus Deff ermittelt werden, sofern der Labyrinthfaktor χ der Struktur aus der Kinetik des Stoffaustausches in den mit einer flüssigen Phase gefüllten Poren separat bestimmt wird. An einem Trägerkatalysator (CuO auf γ-Al₂O₃) ergab sich auf diese Weise ein für die Diffusion maßgebender effektiver Porenradius, der in den Bereich der Makroporen fällt. Ein Vergleich mit dem aus reaktionskinetischen Daten ermittelten effektiven Diffusionskoeffizienten läßt auf eine ungleichmäßige Verteilung der aktiven Komponente im Kontaktkorn schließen.
A microfluidic chip integrating amperometric enzyme sensors for the detection of glucose, glutamate and glutamine in cell-culture fermentation processes has been developed. The enzymes glucose oxidase, glutamate oxidase and glutaminase were immobilized by means of cross-linking with glutaraldehyde on platinum thin-film electrodes integrated within a microfluidic channel. The biosensor chip was coupled to a flow-injection analysis system for electrochemical characterization of the sensors. The sensors have been characterized in terms of sensitivity, linear working range and detection limit. The sensitivity evaluated from the respective peak areas was 1.47, 3.68 and 0.28 μAs/mM for the glucose, glutamate and glutamine sensor, respectively. The calibration curves were linear up to a concentration of 20 mM glucose and glutamine and up to 10 mM for glutamate. The lower detection limit amounted to be 0.05 mM for the glucose and glutamate sensor, respectively, and 0.1 mM for the glutamine sensor. Experiments in cell-culture medium have demonstrated a good correlation between the glutamate, glutamine and glucose concentrations measured with the chip-based biosensors in a differential-mode and the commercially available instrumentation. The obtained results demonstrate the feasibility of the realized microfluidic biosensor chip for monitoring of bioprocesses.