On-line mass spectrometry in fermentation

The on-line application of mass spectrometry (m.s.) includes analysis of the fermentor gas phase by using a capillary inlet and analysis of the liquid phase by using membrane probes. Gas-phase measurements with a capillary inlet are fast and accurate for all gases of interest (O₂, N₂, CO₂, H₂, etc.). Liquid-phase measurements are done with steam-sterilizable membrane inlet probes, permitting direct analysis of dissolved gases and various volatiles. With these two inlets, automatic measurement of both the liquid and gas phases is possible when a microcomputer is used. This was applied to the batch fermentation of Bacillus subtilis. A further application of the membrane probe is evaluation of fermentation process state; this involves measuring the spectra of all detectable volatiles and correlating this information with the process state (e.g., product formation). Sufficient characteristic volatiles were found in various industrial fermentation samples. When mass spectra are treated by factor analysis, useful correlations are found with the product concentrations measured off-line. Calibration depending on the process conditions is necessary for this method, but it is widely applicable and allows automatic monitoring.