A MASS-SPECTROMETRY MEMBRANE PROBE AND PRACTICAL PROBLEMS ASSOCIATED WITH ITS APPLICATION IN FERMENTATION PROCESSES

A sensor-type, multi-compound monitoring system was constructed to mea sure several substances dissolved in a culture medium by use of a memb rane inlet system coupled with a low-cost quadrupole mass spectrometer . The membrane inlet system was shown to have higher sensitivity with an even faster response than a capillary inlet system. The system was able to monitor on-line gaseous (H-2, CO2 and O-2) and volatile (ethan ol, butanol, acetone, acetic acid and ethyl acetate) compounds at conc entrations in a range suitable for fermentation process monitoring app lications. The effects of temperature, agitation speed and pressure on measurements using the membrane inlet system were investigated. For v olatile compound measurements, temperature and pressure had an effect on the response but the agitation speed did not. A high concentration of compounds caused measurement saturation due to the space charge eff ect, but this could be overcome by reducing the surface area of the me mbrane. The system was applied to the monitoring of ethanol in a yeast cultivation. Measurements were affected by CO2 produced during the fe rmentation, but this could be compensated for by means of a linear emp irical equation. The system demonstrated high potentiality for applica tion to the on-line monitoring of multiple compounds in fermentation p rocesses.