Rinse Recovery

How is recovery study performed for Rinse Samples in Cleaning Validation?


Dear sims,

the recovery test for rinse samples is performed analogous to the swab sampling. There are two options: The first one is to get a sample of the surface (for sinterized metals, wire meshs, etc), or a spare part of the piece too intricate to be swabbed (filling needles, valves, etc.), from the manufacturer of the equipment. The other option is to directly spike the part of the equipment that cannot be swabbed.

In all cases the surface or piece has to be spiked with a solution of the analyte, which can be performed with a Hamilton syringe or an automatic pipette, because the quantity of spiking solution needs to be exactly metered. In my experience the Hamilton syringe is superior because the pipette discharges too quickly and may spill some solution, albeit being difficult to spread over the entire surface. Another issue is the homogeneous distribution of analyte, and the advice is to use a dilute solution and a solvent volatile enough to evaporate quickly, but not so volatile that the evaporation cools the piece below the dew point causing humidity to condensate on the piece. Anyway, the distribution is less critical than one would expect, and actual data of how the contamination is distributed on the piece after cleaning are normally lacking.

The decision whether to spike on a sample surface or directly in the equipment is normally subject to great discussion. In my opinion nothing reflects the actual sampling conditions better than spiking in the equipment, (it is hard to believe that one gets the same recovery comfortably sitting at the lab bench, than hanging upside down in a preparation vessel), but it has the disadvantage that the maximum level you can spike is the acceptance level (nobody will allow you to contaminate the equipment on purpose).

Best regards


Dear Sims,

There are few ways you can perform rinse recovery studies. Following are the methods commonly used in industry for performing rinse recovery studies.

STEP I: Select an appropriate solvent (usually organic solvent) to dissolve the target residue under study. In order to expedite drying time and allow an even distribution of the target residue on the surface being studied, the residue stock solution should be made up in suitable organic solvent (e.g. alcohol, chloroform, acetone).
STEP II: Prepare the residue stock solution by dissolving known amount of residue in the solvent.
STEP III: Select the material (e.g. stainless steel, glass, rubber etc.) for conducting recovery studies. Obtain coupons or containers (of appropriate dimensions) made up of same material as the production equipment. Usually 25 cm2 coupons are used for recovery studies, you may select coupons with larger surface area also.
STEP IV: Determine type and volume of rinse solvent. Rinse solvent selected for recovery studies should be the same as the one used for actual rinse sampling. Determine what volume of the rinse solvent would cover the selected surface area (e.g. 5 x 5 = 25 cm2) in actual sampling condition. Make sure that the ratio of rinse solvent to surface area should not be more than the expected ratio under actual rinse sampling conditions. For example, in actual condition if you want to collect rinse sample from an equipment with a surface area of 1000 cm2 using 10 L of rinse solvent then the ratio of volume of the rinse solvent to surface area would be 10 ml per cm2 (10,000 ml / 1000 cm2). This means that you have to use 250 ml of rinse solvent in recovery studies to collect rinse sample from 25 cm2 coupons. Another important factor that should be considered is the temperature of the solvent for the recovery study, it should be the same as that of the actual rinse sampling solvent.
STEP V: Spike the coupon or container with an aliquot of stock solution yielding a concentration equal to 50%, 100%, and 200% of the calculated MACO per cm2 of surface area for the target residue being studied. This can be done by pouring/applying appropriate volume of residue stock solution using a pipette or syringe (as highlighted by Alfred). If the concentration of stock solution is 50 μg/ml and the MACO calculated by usual method is 50 μg/25 cm2, then you need to apply 0.5 ml, 1.0 ml and 2.0 ml to obtain 50%, 100% and 200% of MACO/25 cm2. Spiking residue at three or more concentrations is generally done to study the linearity of the method and is not a regulatory requirement. In case, you are interested in spiking only one concentration then spike residue at only 100% level.
STEP VI: Allow surface to air dry. Repeat each concentration 3 times. “Control” must be included in the study in order to establish a baseline. Note: it is important that all the solvent has evaporated from the surface prior to rinsing.
STEP VII: Conducting rinse sampling: Use any one of the following method to simulate rinsing:
Method A: Position the spiked coupon over a beaker to collect the rinse-sampling solution, then carefully pipette the required volume of rinse solvent over the coupon making certain that all the surface area is contacted by the solvent, and finally let the solution collect in the beaker below.
Method B: Spike the bottom of beakers/containers (made up of selected material of construction) with residue, add a fixed volume of rinse solvent, and agitate. Collect the sample by transferring the rinsate to separate beaker or test tube.
Method C: Place the coupon in an appropriate amount of rinse sampling solvent into the bottom of a beaker and gently swirl for ~30 sec. The coupon and rinse solvent should be separated immediately to stop the dissolution process. (Note: Make sure the underside of the coupon should not come in contact with residue while spiking the residue onto the surface).
STEP VIII: After the simulated rinse sampling, collect the rinse sample and analyze for the target residue and compare with the amount spiked onto the coupon. Residue recovery is then calculated as follows:
[indent]% Recovery = (Amount detected / Amount spiked) x 100[/indent]

Few other issues that are required to be considered include (but are not limited to):
A. Potential interferences
If the excipients can be suspected to interfere with rinse sampling/analytical testing, the spiking of the active should be performed in their presence.
B. Stability considerations

  1. The time between actual cleaning and sampling from the surface and the shelf life of the rinse sample collected needs to be mimicked for the recovery studies.
  2. The ageing effects should be investigated with respect to the actual rinse sampling conditions.

Enjoy performing rinse recovery studies . . . .:slight_smile:

Excellant information