University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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John Villadsen

Abbrev:
Villadsen, J.
Other Names:
Address:
Department of Biotechnology, Technical University of Denmark, DK-2800 Lyngby Denmark
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Citations 4

"A Computational Technique For Simulating The Dynamic Response Of A Flow Injection Analysis System"
Chem. Eng. Sci. 1992 Volume 47, Issue 7 Pages 1591-1600
Steven H. Isaacs and Henrik Soeberg, Lars H. Christensen and John Villadsen

Abstract: A computational technique is presented for obtaining the dynamic response to a gas diffusion module as part of a flow injection analysis (FIA) system. Based on orthogonal collocation, Laplace transformation, and Fourier series, the method provides a relatively quick way to account for dispersive effects occurring via longitudinal convection and lateral diffusion. Simulation examples, including a comparison with a dynamic signal obtained with an actual FIA system, are provided.
Computer Gas diffusion Laplace Simulation Fourier transform

"An Automated Glucose Isomerase Reactor System With Online Flow Injection Analyzers For Monitoring Of PH, Glucose And Fructose Concentrations"
Chem. Eng. Sci. 1990 Volume 45, Issue 4 Pages 1031-1042
Jens Gram and Michael de Bang, John Villadsen*

Abstract: The literature on glucose isomerization with immobilized glucose isomerase has been reviewed with respect to thermodynamics and kinetics of the reaction and the industrial process layout. A laboratory scale fixed-bed reactor for isomerization of glucose with immobilized glucose isomerase has been constructed. A system for sample withdrawal and three flow injection analyzers-measuring glucose, fructose and pH-has been developed, automated and used to monitor the process. The equipment is controlled by a personal computer with interface expansion boards. The isomerization process has been monitored in steady-state operation as well as in pH transients. Using a commercial immobilized glucose isomerase (Sweetzyme Q from NOVO Industri A/S), the isomerization process has been studied with respect to equilibrium conversion, composition of the feed syrup, film diffusion resistance, enzyme deactivation and buffering effect of the immobilized enzyme. The experience from computerization of the equipment and the use of flow injection analyzers is summed up and the potential of such analyzers for monitoring biotechnological processes is discussed.
pH Glucose Fructose pH Immobilized enzyme

"FIA For Online Monitoring Of Important Lactic Acid Fermentation Variables"
Biotechnol. Bioeng. 1989 Volume 33, Issue 9 Pages 1127-1134
J. Nielsen, K. Nikolajsen, J. Villadsen

Abstract: An automated system with semi on-line monitoring of glucose, lactic acid, protein, and optical density during lactic acid fermentations, is set up to study the dynamics of lactic acid bacteria. The analyzers for glucose, lactic acid, and protein are based on flow injection analysis (FIA). The system consists of a laboratory fermenter with a continuous withdrawal system and an analysis system where glucose, lactic acid, and protein concentration are measured together with the optical density of the fermenter sample. The system is controlled by a personal computer. The system response is fast, and it yields a large number of reliable and precise analytical data, whoch is of great importance for mathematical model building. Some premliminary results are shown.
Lactic acid

"Inline Flow Injection Analysis For Monitoring Lactic Acid Fermentation's"
Anal. Chim. Acta 1988 Volume 214, Issue 1-2 Pages 137-145
K. Nikolajsen, J. Nielsen and J. Villadsen

Abstract: A flow injection system is described for the monitoring of lactic acid fermentation products, i.e., lactic acid, glucose and proteins, plus cell density, under personal-computer control. Glucose and lactic acid are determined with use of selective enzymatic (oxidase) oxidation and chemiluminescence detection of the products via the luminol - H2O2 reaction. Proteins are determined via reaction with biuret in a 2-m reaction coil and spectrophotometric detection at 565 nm. The absorbance at 565 nm is also used to measure cell density. Detection limits are ~5 mg L-1 for glucose, 50 mg L-1 for lactic acid and 0.2 g L-1 for proteins (rectilinear calibration ranges 5 mg L-1 to 2 g l-1, 0.1 to 2 g L-1 and 0.2 to 8 g l-1, respectively). The apparatus is particularly suitable for studies of fermentation kinetics.
Glucose Lactic acid Proteins Fermentation broth Chemiluminescence Spectrophotometry Computer Immobilized enzyme Kinetic