Highly sensitive coulometric titration of oxygen for the characterization of solid materials at elevated temperatures

A new setup for characterization of solid material oxygen exchange and conductivity in a broad oxygen partial pressure range and at elevated temperatures is presented. The development target of this setup is directed towards the detection of ultra-low amounts of exchanged oxygen. For this, electrochemical cells made of yttria-stabilized zirconia (YSZ) were optimized and applied in a flow-through arrangement. The design and process measures enable a lower limit of detection below 100&thinsp;pmol of exchanged oxygen. Furthermore, the system characteristics concerning oxygen dispersion, titration efficiency and electrode kinetics are described.</p

Novel probes for pH and dissolved oxygen measurements in cultivations from millilitre to benchtop scale

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)pH value and the concentration of dissolved oxygen (DO) are key parameters to monitor and control cell growth in cultivation studies. Reliable, robust and accurate methods to measure these parameters in cultivation systems in real time guarantee high product yield and quality. This mini-review summarises the current state of the art of pH and DO sensors that are applied to bioprocesses from millilitre to benchtop scale by means of a short introduction on measuring principles and selected applications. Special emphasis is placed on single-use bioreactors, which have been increasingly employed in bioprocess development and production in recent years. Working principles, applications and the particular requirements of sensors in these cultivation systems are given. In such processes, optical sensors for pH and DO are often preferred to electrochemical probes, as they allow semi-invasive measurements and can be miniaturised to micrometre scale or lower. In addition, selected measuring principles of novel sensing technologies for pH and DO are discussed. These include solid-state sensors and miniaturised devices that are not yet commercially available, but show promising characteristics for possible use in bioprocesses in the near future

MINIATURIZED BASIC OXYGEN AND PH SENSORS FOR ELECTROCHEMICAL MEASUREMENTS IN BIOLOGICAL SYSTEMS

After an introduction concerning the importance of pH and 0, concentration in biological systems, two types of sensors were reviewed: 1) amperometric miniaturized electrodes for in vivo oxygen measurements and as basic sensors for glucose measurements, and 2) ISFET pH-sensors with SizN, membrane. The miniaturized po. sensors were tested in vivo using narcotized rabbits and dogs. For the Purpose of use the pH sensors were examined? range of application, service life, sensitivity, long-time drift, temperature drift and time of response

Encapsulation of ISFET sensor chips

The encapsulation of ISFET sensor chips is a challenge to sensor technology and materials. Recently developed new packaging technologies enable reliable and cost effective chip encapsulation. By this, one of the serious problems, which had hindered the large-scale production and industrial application of ISFET sensors over three decades could be overcome now to a large extent. The paper reports both on ISFET encapsulation methods on laboratory level and advanced industrial production technologies. The influence of the packaging design on special applications and on the dynamic behaviour of the sensor is illustrated. Furthermore, sensor materials are characterised and various testing methods are described

Determination of dissolved CO2 concentration and CO2 production rate of mammalian cell suspension culture based on off-gas measurement

The determination of dissolved CO2 and HCO3− concentrations as well as the carbon dioxide production rate in mammalian cell suspension culture is attracting more and more attention since the effects on major cell properties, such as cell growth rate, product quality/production rate, intracellular pH and apoptosis, have been revealed. But the determination of these parameters by gas analysis is complicated by the solution/dissolution of carbon dioxide in the culture medium. This means that the carbon dioxide transfer rate (CTR; which can easily be calculated from off-gas measurement) is not necessarily equal to carbon dioxide production rate (CPR). In this paper, a mathematical method to utilize off-gas measurement and culture pH for cell suspension culture is presented. The method takes pH changes, buffer and medium characteristics that effect CO2 mass transfer into account. These calculations, based on a profound set of equations, allow the determination of the respiratory activity of the cells, as well as the determination of dissolved CO2, HCO3− and total dissolved carbonate. The method is illustrated by application to experimental data. The calculated dissolved CO2 concentrations are compared with measurements from an electrochemical CO2 probe

Core-Hole Screening as a Probe for a Metal-to-Nonmetal Transition in Lead Clusters

Metal clusters serve as model systems to study basic problems of electronic correlation. Vacuum ultraviolet light from the free electron laser FLASH ionizes 5d electrons from mass separated negatively charged clusters, thus transiently leading to core ionized neutral systems. Shielding of the core hole affects the electron binding energy. From the strong deviation from expectations of the metallic droplet and jellium models we conclude on reduced electronic shielding once the cluster size falls below about 20 atoms. This suggests a metal to nonmetal transition, in agreement with previous local density approximation calculation