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Application of Fiber‐Optic Fluorescence Measurements to On‐Line pH Monitoring of a Pseudomonad Fermentation Process
Author(s) -
Kisaalita W. S,
Slininger P. J,
Bothast R. J,
Mccarthy J. F,
Magin R. L
Publication year - 1991
Publication title -
biotechnology progress
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 129
eISSN - 1520-6033
pISSN - 8756-7938
DOI - 10.1021/bp00012a012
Subject(s) - fluorophore , fluorometer , fluorescence , fermentation , ionic strength , biocompatibility , chemistry , analytical chemistry (journal) , aeration , ph meter , pseudomonas fluorescens , materials science , chromatography , optics , biochemistry , aqueous solution , bacteria , physics , organic chemistry , biology , genetics
This article reports results on the application of fluorophore‐based pH sensing to the monitoring of fermentation processes. Emphasis is placed on identifying potential strengths and limitations. A custom‐built fluorometer, designed to provide broad‐band excitation (<420 nm) was used to monitor the emission of a pH‐sensitive fluorophore (1, 4‐dihydroxyphthalonitrile) in solution at two wavelengths. The overall sensing system was characterized with respect to biocompatibility, response, and stability. The biocompatibility results revealed that the growth rate of Pseudomonas fluorescens (NRRL B‐15132) was decreased by the fluorophore at high concentrations (≥100 μM). Correlating the observed pH with the ratio of the two wavelengths (488 nm/434 nm) rendered the pH‐sensing system immune to factors such as fluorophore oxidation, aeration, and reactor agitation. A comparison of response times for fluorescence and Ingold pH measurements revealed fluorescence sensing to be slower. This was attributed to imperfect mixing and position differences between the two sensors in the fermentor. During the course of fermentation, on‐line ratiometric pH measurements for NRRL B‐15132 batch process were affected by changes in ionic strength and cell concentration. A pH difference of 0.66 was recorded (using an Ingold electrode as the standard) after 120 h of the fermentation. Recommendations for overcoming limitations were made.