Industry is seeing a shift to single-use biopharmaceutical manufacturing methods, prompting a need for new pH measurement approaches to overcome instrumentation challenges.
Scientist working with a bioreactor for cell culture
Monitoring and historizing the pH of a process media batch, and often using this value for control and automation, is commonly required for biopharma processing operations. Traditional production and instrumentation methods are well understood, but as the industry has adopted single-use production methods, it has become clear that classic sensors can’t deliver the necessary longevity, accuracy, and convenience.
Conventional fixed-in-place stainless steel technology (SST) equipment has been the norm for biopharma installations of all size. In recent years, many operations have shifted to advanced single-use technology (SUT), where fixed bioreactor vessels are replaced by disposable bioreactor bags. Once the sterility and durability of these single-use system (SUS) designs became practical, many biopharma manufacturers realized benefits in flexibility, scalability, and cost-savings.
SST equipment must undergo expensive clean-in-place and sterilize-in-place operations, which can negatively affect installed sensors. In comparison, SUT installations avoid many of these costs and hazards, although instrumentation designs must be addressed.
Traditional pH sensing methods use glass bulk sensing technology which must be in direct contact with the process media, and for SST systems these sensors must be removed or protected during cleaning and sterilization.
Some early versions of single-use pH sensors used dry storage, but the sensor could not be tested or calibrated until just before the bioreactor bag was put into service. Even sensors using wet storage could be affected by the gamma radiation sterilization, experience high drift, or have an unacceptably short shelf life.
To address these issues, Emerson’s Rosemount developed a combination of new technologies:
- A single-use bag fitting was created to maintain aseptic integrity, prevent leakage, and withstand sterilization radiation.
- The sensor is arranged in a retractable chamber so it can be stored and calibrated in a wetted state, and then extended into contact with process media just prior to batch startup.
- A specially developed phosphate-based buffer solution remains stable after irradiation, can be used for calibration, and provides a two-year shelf life.
- The sensor itself is therefore compatible with established measurement technologies.
Storing the sensor under optimized wet conditions helps achieve a stability of less than 0.005 pH drift per day, making it a good fit for long production runs of up to 20 days without recalibration. Once a single-use pH sensor is in service, users can obtain a process grab sample at any time and perform an updated one-point calibration against it to reset any sensor drift as needed, ensuring the sensors can be used for production runs of any duration.
Because single-use technologies and production approaches are being implemented more often, end users should ensure they are specifying the latest generation of instrumentation. SUT-specific pH instrumentation, like the Rosemount 550pH, are made to address single-use challenges, delivering the best performance and value.
If your facility is taking advantage of single-use processing, have you looked into the benefits of pH and other sensors developed by Emerson specifically for use with SUT?
Visit the Liquid Analysis pages at Emerson.com for more on technologies and solutions for continuous inline measurement of process liquids. You can also connect and interact with other engineers in the Life Sciences and Measurement Instrumentation Groups at the Emerson Exchange 365 community.
