How to Perform Swab and Rinse Recovery Studies

Analytical methods are demonstrated to be appropriate for their intended purpose through validation. For cleaning analytical methods (i.e., methods used to quantify previous product residue on equipment surfaces), the sampling techniques used must also be demonstrated to be effective through recovery studies.

Recovery studies can be performed as part of the method validation or through a separate protocol to demonstrate that a sampling method can effectively recover residues from equipment surfaces. It is important to note that the method's accuracy and the sampling technique’s recovery are distinct, although they use similar nomenclature. The accuracy of the method demonstrates the bias inherent to the method itself, while the recovery describes any physical loss of residue from the sampling technique. To elaborate using an example, if an HPLC method measures a 10 ppm sample and gives a result of 9.5 ppm, the analytical method has 95% recovery and is 95% accurate. Conversely, if 10 ppm of residue is spiked on a surface and then the surface is swabbed, and that same HPLC method only measures 7 ppm, that means the sampling recovery is only 70%, as there is a 30% loss due to a combination of the method’s accuracy and unrecovered residue.

In either case, the study should be performed prior to the routine use of the sampling method. The protocol guiding the recovery study should define the residue being sampled, the materials of construction (MOCs) to be tested, and the acceptance criteria for recovery. All the equipment’s product contacting MOCs should be challenged as part of the recovery study. If a product contact MOC will not be challenged, justification for exclusion should be documented in the protocol.

Swab and rinse recovery studies involve spiking MOC coupons with standard solutions of the residue prepared at three concentrations in triplicate. The concentrations spiked typically include the limit of quantification of the analytical method, the cleaning limit of the product, and 120% of the cleaning limit. When spiking the coupons, ensure the residue is uniformly distributed across the coupon surface, then allow the residue to dry to simulate manufacturing conditions.

For swab and rinse recovery studies, the sampling technique and sample preparation are different. For example, when performing swab recovery, the spiked coupon should be swabbed using a systematic technique consistent with what is performed in the manufacturing area. To ensure adequate recovery, the swab technique should:

• Condition the swab in an appropriate solvent before use

• Express the swab head after conditioning to remove excess solvent

• Follow a set pattern (e.g., left to right and top to bottom)

• Apply even pressure to ensure the entire swab head remains flat to the surface

• Flip the swab head when changing stroke direction

After sampling, the swab should be sealed in a container with extraction solvent to keep the swab wet.  Agitation techniques such as vortexing or sonication should be performed as part of sample preparation to aid in releasing the residue from the swab into the solvent. The agitation technique parameters (vortex or sonication level) and time are critical and should be consistent between the recovery study and the standard test procedure (STP) that will be used for routine analysis.

For rinse recovery, the sampling technique used should be representative of actual rinse sampling performed on manufacturing equipment. Typically, to simulate cascading flow over the equipment surface, the spiked coupon is held at an angle (usually 45°) and rinse solvent is poured at the top of the coupon allowing the solvent to cascade over the spiked residue, which is then collected in a separate beaker or vial. The coupon flow should simulate the manufacturing equipment rinse flow/surface area ratio.  Rinse recovery studies should not add additional steps to improve recovery that are not be performed when sampling equipment surfaces, such as soaking the spiked coupon in the rinse solvent.

Analysis of the swab and rinse samples is conducted using a validated method such as liquid chromatography (LC), ultraviolet (UV), or total organic carbon (TOC) to quantify the extracted residue. The recovery factor is calculated by comparing the amount of residue recovered to the amount initially applied to the coupon using the formula below:

• Increasing vortexing or sonication time may allow for more release of residue from the swab

• Changing to an extraction solvent that the residue is more soluble in is likely to increase recovery

• Changing the type or size of swab head or adding additional conditioning steps to prevent leeching and interference with analytical results

• Adding additional swab directions (e.g., diagonal or zig-zag patterns) may allow for more recovery of residue

If the recovery is demonstrated to be 50% or less and the method cannot be improved, then a written justification should be provided as to why the method is acceptable for use and what improvements were attempted.

The results of recovery studies should be documented in detail, including test conditions, recovery factors, and any deviations observed. The lowest average percent for any concentration and MOC recovery should be selected as the worst-case recovery factor for the respective sampling technique. To properly integrate swab or rinse recovery factors into the cleaning program, the cleaning limit should be multiplied by the recovery factor to account for residues remaining on the equipment surface that were not extracted during sampling. For example, a cleaning limit of 10 ppm with a 65% recovery factor should be adjusted to a limit of 6.5 ppm to ensure the analytical testing performed is representative of the potential residue on the surface.

While it is still considered acceptable in industry guidance’s to use a correction factor, in Mindful Quality’s experience, it is difficult for companies to ensure correction factors are consistently and contemporaneously applied to correct individual analytical results. If a correction factor is used, procedural controls should be put in place to ensure the correction factor is applied to individual results consistently and contemporaneously. Mindful Quality recommends the use of a recovery factor to correct the cleaning limit.

Recovery studies qualify the sampling techniques in combination with the cleaning analytical method to demonstrate they are appropriate for their intended use. Establishing the recovery factor of sampling techniques is essential to ensure that limits are appropriately adjusted to account for any potential loss during sampling. Swab and rinse recovery studies are critical to demonstrate that the sampling methods effectively recover residues from equipment surfaces, ensuring that cleaning validation results accurately represent the true level of cleanliness and provide confidence that established limits are scientifically justified.

References

1. ASTM International. (2023). E3418-23: Standard practice for calculating scientifically justifiable limits of residues for cleaning of pharmaceutical and medical device manufacturing equipment and for medical devices. ASTM International.

2. Health Canada. (2021). GUI-0028: Cleaning validation guide. Government of Canada.

3. International Society for Pharmaceutical Engineering (ISPE). (2020). Guide: Cleaning validation lifecycle - Applications, methods, and controls. ISPE.

4. Parenteral Drug Association (PDA). (2012). Technical report no. 29: Points to consider for cleaning validation. PDA.

Contributors: Jenna Carlson, Tim Cirbo, Alec Fufidio, Joanna Joseph, Helen Stranahan, and Harrison Sweeney