Potential of On-Line CIMS for Bioprocess Monitoring

Chemical‐ionization mass spectrometry (CIMS) using flow reactors is an emerging method for on‐line monitoring of trace concentrations of organic compounds in the gas phase. In this study, a flow‐reactor CIMS instrument, employing the H3O+ cation as the ionizing reagent, was used to simultaneously monitor several volatile metabolic products as they are released into the headspace during bacterial growth in a bioreactor. Production of acetaldehyde, ethanol, acetone, butanol, acetoin, diacetyl, and isoprene by Bacillus subtilis is reported. Ion signal intensities were related to solution‐phase concentrations using empirical calibrations and, in the case of isoprene, were compared with simultaneous gas chromatography measurements. Identification of volatile and semivolatile metabolites is discussed. Flow‐reactor CIMS techniques should be useful for bioprocess monitoring applications because of their ability to sensitively and simultaneously monitor many volatile metabolites on‐line.