biostudies-literatureDu NU.S. Department of EnergyEdna Bailey Sussman FoundationGordon and Betty Moore FoundationRobert Buzzelli Endowed Fellowshipe0199125https://www.ebi.ac.uk/biostudies/studies/S-EPMC6008153biostudies-literatureUnknown13(6)The photosynthetic quantum yield (Φ), defined as carbon fixed or oxygen evolved per unit of light absorbed, is a fundamental but rarely determined biophysical parameter. A method to estimate Φ for both net carbon uptake and net oxygen evolution simultaneously can provide important insights into energy and mass fluxes. Here we present details for a novel system that allows quantification of carbon fluxes using pH oscillation and simultaneous oxygen fluxes by integration with a membrane inlet mass spectrometer. The pHOS system was validated using Phaeodactylum tricornutum cultured with continuous illumination of 110 μmole quanta m-2 s-1 at 25°C. Furthermore, simultaneous measurements of carbon and oxygen flux using the pHOS-MIMS and photon flux based on spectral absorption were carried out tPloS oneSimultaneous quantum yield measurements of carbon uptake and oxygen evolution in microalgal cultures.PMC6008153GMBF3828DE-EE0003373DE-SC0008593Allen AEGholami PKline DIDuPont CLMendola DMitchell BGMartz TDu NDickson AGfalseSimultaneous quantum yield measurements of carbon uptake and oxygen evolution in microalgal cultures.The photosynthetic quantum yield (Φ), defined as carbon fixed or oxygen evolved per unit of light absorbed, is a fundamental but rarely determined biophysical parameter. A method to estimate Φ for both net carbon uptake and net oxygen evolution simultaneously can provide important insights into energy and mass fluxes. Here we present details for a novel system that allows quantification of carbon fluxes using pH oscillation and simultaneous oxygen fluxes by integration with a membrane inlet mass spectrometer. The pHOS system was validated using Phaeodactylum tricornutum cultured with continuous illumination of 110 μmole quanta m-2 s-1 at 25°C. Furthermore, simultaneous measurements of carbon and oxygen flux using the pHOS-MIMS and photon flux based on spectral absorption were carried out t2018-01-01T00:00:00Z20182025-04-21T19:25:45.931Z2019-03-26T23:42:34ZS-EPMC60081532992056810.1371/journal.pone.0199125