Post Clean Rinsing Part 2 - PAT

I have been asking around in various forums and contacts in the USA re final rinse practices, and have found that there appears to be a fairly even split between the “conventional” validation of cleaning using a fixed volume of final rinse water and those using a “variable” volume of rinse water to achive a set (pH or conductivity) set point.
The latter would seem to suggest (1) that the process is not “in control” however it does fit well with (2) PAT philosphy.
Has anyone had experience justifying the latter during regulatary inspections?

I will suggest that we should be using fixed volume of final rinse water which was validated by using a specific swab test and supported by a non-specific test like pH or conductivity. This will demonstrate that cleaning process is in control and each time we clean will consistently capable of removing product residue from the equipment surface.

I don’t think regulators will be satisfied with just by monitoring or measuring pH or conductivity after final rinse. This will not suffice the cleaning validation requirements unless it was supported by product specific test.

In this case i would suggest that we establish the final rinse volume (end point) for pH and conductivity during validation alongside specific test. Use the established values used for routine monitoring under PAT.


mmm - I don’t think that I have any worries obout using defined volumes of pre-rinse and cleaning agents at stated temperatures and contact times. That has already been performed along with coupon tests, TOC and product specific HPLC based tests. Following the cleaning phase though - where we have already demonstrated complete removal of the product, we are now rinsing with phosphoric acid (nutralises the sodium hydroxide, and may have a re-passivating effect) and then a final rinse to remove the phosphoric acid. As this is just a nutralising stage and not a cleaning stage can a variable volume of final rinse water be justified?

Dear Trefor,

once you have correlated pH and/or conductivity data with actual residues of phosphoric acid and reached a specification for the pH/conductivity limits, I don´t think regulators will have any problem with a variable rinsing volume. To be on the safe side I would suggest to establish a minimum rinsing volume (set with the data from the correlation of residue vs. pH/conductivity), and a variable portion to actually achieve the pH/conductivity limits. If the minimum rinsing volume was correctly set, you will never need the additional variable portion. If there is any need for the variable portion, you are still covered regarding residue limits and do not need to initiate a deviation.

Best regards


Thanks for your clarification on final rinse, this concept may be acceptable in a completely controlled automated environment with procedures in place. However with my experience in CV I don’t think any regulators will except the concept of “test until pass”.