Differential Pressure Monitoring in Sterile Filtration
How do you ensure the sterile filtration filter is performing as expected?
July 15, 2021
In the first and second part of our “Filtration Nation” blog series, we discussed the importance of prefiltration and integrity testing for sterile filtration. This week, we turn our attention to differential pressure monitoring in sterile filtration and tracking your filter’s performance in real-time, ensuring optimal filter performance.
Sterile filtration is frequently taken as a given in a lab protocol. It worked the last time we ran it, why shouldn’t it work this time? How often does a researcher grab a filter, remove it from its packaging, connect it to a hose and just start filtering? It is important to remember that filters are delicate pieces of equipment and can easily become damaged or blocked, allowing unwanted materials through. How can you tell that something is not quite right with your sterile filtration as soon as it happens? In our recent Sterile Filtration Scientific Brief, Joseph Baaklini discusses this problem and explains that differential pressure monitoring is the answer.
How does differential pressure monitoring work?
Simply stated, differential pressure is the difference between the pressure immediately upstream and immediately downstream of the sterile filter. I.e., it is a measure of the pressure drop across the filter. Thus, differential pressure = pressure drop = ΔP
A properly performing filter will have a differential pressure that stays within a pre-determined range. By monitoring the differential pressure over time, an operator can be sure the filtration process is proceeding as expected, and importantly will be alerted to any problem as it occurs. However, the acceptable range of differential pressures for any given process will change over time, (as shown in the typical life curve graph of a disposable filter on the right), and it is important for the operator to understand this evolution as it pertains to their particular set up.
In short, the acceptable differential pressure will increase over time as unwanted particulates are removed from the liquid by the filter and start to accumulate on the upstream side of the filter. This is normal and must be accounted for in any differential pressure monitoring so that the process is not deemed to be incorrectly out of spec. Operators can also set cut-off pressures that tell them when the process should be paused, and the current filter changed out for a new one (more common in continuous workflows).
Knowing these key parameter values and monitoring differential pressure to see when you have hit them goes a long way to improving the consistency of your process and ensuring your sterile filtration is working as expected every time. In the event that a problem does occur, having a log of the differential pressure over time goes a long way to help eliminate the guesswork or time-consuming fault finding that would otherwise be required.
The full Scientific Brief on differential pressure in sterile filtration goes into much more depth on the theory and practice. You can find this brief on our Scientific Resource Hub, along with a host of other concise, highly focused briefs dealing with all the major issues, concerns, and challenges of filtration. Stay tuned for Part 4 where we will further discuss how to improve sterile filtration.