Online concentration measurement, sensor

As online detectors, when sensors that measure the concentration of the analyte of interest are integrated into a flow line system. " ... 

The physiological state and concentration of microorganisms in a batch or a fed-batch process change as a fermentation progresses therefore, it is desirable to determine current control strategy (set-point) in real time based on current process variables. However, the limited availability of online sensors to measure... 

Meyerhoff C, Mennel FJ, Bischof F, Sternberg F, Pfeiffer EF. Combination of microdialysis and glucose sensor for continuous online measurement of subcutaneous glucose concentration theory and practical application. Hormone and Metabolic Research 1994, 26, 538-543. 

Biosensors. Sensors are required to adequately monitor bioreactor performance. Ideally, one would like to have online sensors to minimize the number of samples to be taken from the bioreactor and to automate the bioreactor process. Most bioreactors have autoclavable pH and dissolved oxygen (D.O.) electrodes as online sensors, and use offline detectors to measure other critical parameters such as glucose and glutamine concentration, cell density, and carbon dioxide partial pressure (pC02). An online fiber-optic-based pC02 sensor is commercially available and appears to be robust.37 Probes are also commercially available that determine viable cell density by measuring the capacitance of a cell suspension. Data from perfusion and batch cultures indicate that these probes are reasonably accurate at cell concentrations greater than 0.5 X 106 cells/mL.38,39... 

Continuous, or very frequent, automated measurement of individual or groups of toxic compounds or general physico chemical properties, can provide a rapid warning of changed environmental conditions. A few chemical methods (such as the LC SAMOS for polar compounds (Slobodnik et al., 1992)) may even detect the occurrence of high concentrations of specific contaminants of concern at the test site. In situ, online and on-site approaches are described in other chapters of this volume, but as yet, application is restricted by the limited availability of suitable, sufficiently sensitive and selective (bio)sensors and monitors for the analysis of (priority) pollutants that need to be monitored. Once available, they may provide (semi)-qualitative and quantitative information on the occurrence of compounds in the waters. 

The SMBR plant is equipped with several sensors the temperature of the columns and the incoming streams are kept at around 60 °C by a closed heating water circuit that is controlled by a thermostat. Concentrations in the product line and in the recycling loop are measured online using a combination of a density measurement unit and a polarimeter (Jupke et ah, 2002). The pressure in the recycling loop (i.e. at the inlet of the recycling pump) is maintained constant using a P-controller that varies the extract flow rate. 

A turbidostat mode of operation relies on the use of a sensor to measure the biomass concentration in the photobioreactor. Such a sensor can be based on the online measurement of culture turbidity, for example, but any other biomass sensor can be used as well. Based on such a continuous biomass measurement the flow rate through the system then is automatically adjusted such that the biomass concentration is maintained at a preselected value (Fig. 29). 

Responsive hydrogels are valuable materials for sensors, especially for sensor application in liquids, for example, online control of composition of a liquid, measurement of pH, and concentration of ions. The sensitivity of the gel depends on its chemical stmcture and can be modified in a wide range. 

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