The drift voltage is one of the key experimental parameters of any drift tube ion mobility spectrometer. In this work, we show that a universal relationship between optimum drift voltage and the resolving power reached at this point exists, governed only by temperature and ion charge state. With these two quantities known, the measured optimum drift voltage and resolving power combination can be used to estimate the ideality of the drift conditions inside a drift tube, since any deviation from the theoretical values must be caused by non-idealities in the ions' drift. Analyzing drift voltage sweeps from nine different ion mobility spectrometers, a continuous increase in drift tube ideality over the past is observed, reaching from less than 50% thirty years ago to 99% for a current design based on printed circuit boards. Furthermore, possible causes for the observed non-idealities are discussed.
To ensure high quality output of biotechnological processes, relevant process parameters need to be monitored. As bioprocesses are increasingly executed in single use bioreactors, there is an increasing demand for new sensors applicable to these processes. In this work, we investigate different approaches for continuous non-invasive cell growth monitoring, especially for single use bioreactor applications. Therefore, the permittivity of the cell culture is used as a measure for the biomass. In a first step, a measuring procedure based on the transmission measurement of an electromagnetic wave is investigated. It appears that the penetration depth of this sensor is not sufficient for a noninvasive measurement through the polymer wall of a single use bioreactor. Therefore, alternative setups based on magnetic induction are investigated. The initial setup is very simple. It consists of a planar coil connected to an impedance analyzer. The coil is attached to the outside of the polymer foil of the single use bioreactor and an impedance spectrum is measured. To evaluate the sensor, E. coli cultivations are performed in a modified cultivation setup, which enables measurements through the polymer foil of a Sartorius BIOSTAT® CultiBag RM, and additionally allows sampling of culture medium for optical density reference measurements. The resonance peak of the coil in the impedance spectrum, is observed as measure for the optical density. Regardless of the simple sensor construction, we found a good correlation between optical density and the damping ratio of the resonance peak. However, the sensor signal shows saturation towards high optical densities. Therefore, an LTCC coil producing a higher magnetic flux density in the culture medium is investigated subsequently. This sensor shows a linear response up to high optical densities, but the sensitivity is reduced compared to the former used coil and therefore scattering of the data is increased. However, to increase the sensitivity, a linear variable differential transformer is realized. Using this setup, the influence of the primary magnetic flux is eliminated from the measuring voltage. This approach delivers the most promising results, as the sensor response is linear up to high optical densities and data scattering is low. Fig. 1. Four-electrode measurement without (left) and with (right) polymer foil (CST Simulation at 1 kHz with discrete port excitation (1 V Amplitude), 190000 Hexahedral Mesh cells and open (add space) boundaries).
Abstract:In this work, we present a low-cost sensor system for continuous non-invasive cell growth monitoring, especially for single use bioreactor (SUB) applications. The sensor system is based on a differential transformer. Using this differential setup, the influence of the primary magnetic flux is eliminated from the measuring signal, enabling highly sensitive non-invasive detection of permittivity changes in the culture medium. To evaluate the sensor, E. coli cultivations are performed and the cell density is measured through the polymer foil of a SUB. We found a linear dependency with low data scattering between measuring signal and cell density.
ZusammenfassungWährend der Implantation von Cochlea-Implantaten muss eine Verletzung bzw. Reizung des Gehörganggewebes vermieden werden. Ziel der vorliegenden Arbeit ist eine Echtzeitüberwachung der Position eines Cochlea-Implantats basierend auf einer kontinuierlichen Messung der Impedanz zwischen den Elektroden des Implantats während der Insertion bereitzustellen. In diesem Beitrag werden erste Modell-Messungen in verschiedenen Medien vorgestellt.
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