Online density determination

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... 

For homogenous systems, the ultrasonic velocity is related to the ratio of modulus to density. Thus, one may expect that any method that determines density changes with adequate precision can provide indication of miscibility [Singh and Singh, 1983]. The ultrasonics can also be used as a screening method for the optimization of processing and its parameters, e.g., for the online characterization of polymers blends [Piau and Verdier, 1993 Verdier and Piau, 1995 Gendron et al, 1995]. 

As the system is aqueous based, it is routinely used for the analysis of nonvolatile analytes with no need for derivatization of sample to maintain analyte solubility. A typical LC system experiences lower diffusion rates than GC because the mobile phase has a higher viscosity and density. LC can be coupled online to sensitive electrochemical and fluorescence detection units. This is an important consideration for the analysis of EDCs present at low concentrations in environmental matrices. Both UV and EC detection were applied to the determination of estrogenic compounds in water samples using LC. 

Product quality is usually determined and certified off-line in a quality control laboratory to ensure that specified properties of a production batch fall within the established range. Specifications related to molecular weight, charge density, composition, particle size, viscosity, rate of dissolution, solution viscosity, and residual monomer are common. Production batches that do not meet the specifications either require further processing, rework, or disposal and reduce production efficiency. As online analytical methods are employed, first pass yields (the proportion of production that meets specifications the first time) usually increase. 

U-tube density cell (ASTM D-4052 method), viscosity by a Stabinger viscosity cell (ASTM D-7042 method), and boiling point distribution by ASTM D-86 method. The gas product was analyzed by online gas chromatograph. Physical properties of the catalyst such as bulk density and total pore volume using the Brunauer-Emmett-Teller (B.E.T.) technique were determined by ASTM C-29 and ASTM-4222 methods, respectively. 

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