Rinse Sample Volumes

When collecting rinse samples, is there a systematic way of determining what volume to use? i.e., X mL of rinse sample per squared inch of contact surface area. Thanks.

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Dear wolverine97,
It should be written in the “rinse sample collection” SOP to how much rinse volume has to collect i.e. 50 ml, 100 ml.
There is no such calculation for X mL of rinse sample per squared inch of contact surface area.
We take rinse sample for analysis by considering that it covers whole surface area how big the area might be…
I hope this might clear your doubt.

Dear wolverine97,

as prashant.chawla says, there is no calculation for the rinsing volume. The right rinsing volume has to be found by try and error to get an acceptable recovery starting with high volumes and trying to use the minimum amount of solvent to avoid unnecessary dilution of the sample. The rule of thumb for a starting point is a volume between 0,5 - 1 ml/cm², but it is strongly dependant from how intricate the sampled surface is (a wire mesh requires far higher volumes than a stainless steel filling needle). Take into account that, to standardize the sampling conditions, the solution collected after sampling needs to be adjusted to a standard volume, because the amount of solvent to rinse is not recovered 100% due to losses by evaporation and solvent remaining on the sampled surface.

Best regards


Thanks a lot folks. Your responses are very helpful.

Dear Mr. Wolverine97,

There are few possible approaches which you can use for determining the volume of rinse solvent to be used, which are:

I – As per the current cleaning procedures for the equipment (or its parts), determine approximate volume of water (purified water) used for final rinse (generally most of the cleaning procedures involve this step and the amount of water used is considered sufficient enough to cover whole of the equipment). Assuming volume of rinse solvent used (for rinse sampling) = volume of water used for final rinse, determine the cleaning validation acceptance limit (in µg/ml or mg/ml i.e. amount of residue/unit volume of rinse). Check if this value is greater than the LOD or LOQ of your analytical method. If yes (which indicates you are not diluting the residue to high extent), then calculate the proportional amount of rinse solvent required to cover a surface area of 25 sq cm (or 100 sq cm, depending on the surface area of coupons used for recovery studies). Perform recovery studies using this much volume of rinse solvent and check if you can get good recovery. If you are getting %recovery less than the one which is desired, you may play around with the volume of rinse solvent in the lab itself to get the desired %recovery. If your acceptance limit is lower than the LOD/LOQ value then in that case you have to consult your analytical chemist, check out if he/she can help to test the residues at that level by either increasing the injection volume (in case if you are using HPLC method) or lowering down the LOD/LOQ value.
II – Perform simple experiments in lab, spike the required amount of residue on the coupons, dry and using a measuring pipette rinse the surface of coupons with the rinse solvent. Determine how much amount of solvent is sufficient enough to remove the residue from the surface. For this you may either use visual observation (if the residue is visually detectable at the spiked level) or test the rinsate collected (depends on the availability of resources). Once determined, you may estimate the amount of rinse solvent to be required for whole equipment or its part. This approach may work for equipment parts or small equipments such as sieves. However, in case of large tanks or equipments with homogenizers/mixers you have to check if the amount of rinse solvent used complies with the requirement of “minimum volume of liquid required” level for its operation.
III - Another approach is the one which is applicable for equipments with spray balls or build-in CIP systems. Volume of rinse solvent should be equal to the volume of solvent used for spray ball coverage studies (if it has been conducted for equipments at your plant).

Whatever approaches you use for determining volume of rinse solvent make sure analytical department is informed and engaged so that they can work out at their side of how to deal with over-diluted samples or LOD/LOQ issue.

Hope this makes your life easy . . :smiley: