By Christian Klinger, Roche Pharma Technical Development, Penzberg, Germany and Ulrike Becken, Eppendorf Bioprocess Center, Juelich, Germany
The pH of the culture medium is a critical process parameter in mammalian and microbial bioprocesses. To successfully transfer processes between bioprocess systems and sites – in the course of process development and scale-up, for example – it is essential to ensure that pH readings in the different systems are comparable. Bioprocess engineers use offline pH measurements for the recalibration of online pH sensors. These can be inaccurate, because factors like sensor age, temperature, and CO2 degassing influence the measurements, making direct cross-site comparisons of pH values difficult. In this application note, bioprocess engineers from Roche Pharma Technical Development describe a method for accurate in-line pH sensor recalibration based on CO2 concentration in the exhaust, using a DASGIP® GA4 exhaust analyzer. This method allows effectively matching of the starting pH of carbonate-buffered systems in process transfers, scale up and scale down; cross plants, sites, and scales.