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Cahill B.P.,Institute of Bioprocessing and Analytical Measurement Techniques | Land R.,Institute of Bioprocessing and Analytical Measurement Techniques | Land R.,Tallinn University of Technology | Nacke T.,Institute of Bioprocessing and Analytical Measurement Techniques | And 3 more authors.
Sensors and Actuators, B: Chemical | Year: 2011

We present an electrode arrangement for the inline measurement of the conductivity of droplets in segmented flow by impedance spectroscopy. We use a thin-walled glass capillary with electrodes contacting the outer surface, so that the contactless measurement of conductivity of the liquid within the capillary is possible. The surface of the glass capillary is silanized resulting in a single hydrophobic surface across which droplets can freely move. We model the impedance of such insulated electrodes and use the model to optimize the electrode system. Measurement of solutions with various salt concentrations allows the performance of the electrode structure to be characterized. Subsequently, the measurement of the impedance response of the aqueous segments in two-phase flow was demonstrated. Measurements were firstly performed with an impedance analyzer and subsequently with a multi-sine measurement setup that is better suited to high-speed measurement of droplets. Previous electrical measurements of segmented flow sensed the difference in dielectric constant between the aqueous phase and the carrier fluid through measurement of capacitance. This work describes an electrical measurement of the conductivity of droplets in segmented flow, that is, the sensor senses a variable property of the droplet itself. © 2011 Elsevier B.V.


Nacke T.,Institute of Bioprocessing and Analytical Measurement Techniques | Barthel A.,Institute of Bioprocessing and Analytical Measurement Techniques | Frense D.,Institute of Bioprocessing and Analytical Measurement Techniques | Meister M.,Institute of Bioprocessing and Analytical Measurement Techniques | Cahill B.P.,Institute of Bioprocessing and Analytical Measurement Techniques
Chemie-Ingenieur-Technik | Year: 2013

Contamination-free process measurement is essential for efficient monitoring of fermenters. This contribution introduces the use of high-frequency sensors for the contactless measurement of the permittivity and conductivity of fermentation media. As microwaves can penetrate through plastic materials without much attenuation, it is possible to achieve measurement setups that can measure the media under test without any direct contact and with long-term stability. The sensor can be installed directly to the outer surface of the fermenter or can be clamped onto tubing. Copyright © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Buchner K.,Institute of Bioprocessing and Analytical Measurement Techniques | Ehrhardt N.,Institute of Bioprocessing and Analytical Measurement Techniques | Cahill B.P.,Institute of Bioprocessing and Analytical Measurement Techniques | Hoffmann C.,Institute of Bioprocessing and Analytical Measurement Techniques
Thin Solid Films | Year: 2011

Internal reflection ellipsometry was used for detection of the consecutive coating of two polyelectrolytes, poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), onto a tantalum pentoxide (Ta 2O 5) substrate until the 10th bilayer. The UV patterned PAH-PAA-multilayer was characterized in air via ellipsometry and atomic force microscopy. Suited optical models enabled the determination of the layer thicknesses in wet and dry states. Linear multilayer formation could be proved by Attenuated Total Reflection - Fourier Transformed Infrared Spectroscopy measurements following the increase of the ν(C=O) band depending on the adsorption of the PAA. Streaming potential measurements after each layer deposition step indicated a change in surface charge after each layer deposition due to the consecutive coating of PAH and PAA. In this article the internal reflection ellipsometry is shown to be a convenient possibility to analyze the modification of a thin transparent Ta 2O 5 substrate. © 2011 Elsevier B.V. All rights reserved.

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