Which method is used to validate the cleaning process by collecting samples from surfaces?

• A. Air sampling
• B. Liquid sampling
• C. Swab sampling
• D. Wipe sampling

Answer: (D)

Testing surface cleanliness relies on a method that physically retrieves residues from the surface so they can be quantified. Wipe sampling achieves this by wiping a defined area with a moistened wipe, then analyzing the residue collected on the wipe. This approach standardizes the sampling process: a specific surface area, a consistent wipe, and a fixed solvent all contribute to reproducible recovery and reliable data. Because the goal is to assess what remains on the surface itself after cleaning, wipe sampling provides a direct measure of surface cleanliness and can be tied to predefined acceptance criteria for residues.

Air sampling looks at contaminants in the air, not on surfaces, so it doesn’t directly validate surface cleanliness. Liquid sampling would assess residues in a liquid phase rather than on the surface. Swab sampling can retrieve material from a surface, but it is typically better suited for small areas or irregular shapes and can be more variable due to contact efficiency. In cleaning validation, the need for a consistent, scalable method across larger, flat surface areas makes wipe sampling the preferred choice for validating how well a cleaning process removes residues.