Determining of swab/rinse sampling area

Hi, I’m new to the site, but not really to the science of CV.
How do you determine and/or calculate the sampling area for swabbing; for rinsing? i.e. 10cm x 10cm sampling area - how do you determine that you need a 10cm x 10cm area and not a bigger or smaller area?
Thanks for the feedback…

Dear joeyb,

as far as i know there is no specific reason why to stick to 100 cm² as a sampling area. In practice it is an area easily covered with a reasonable quantity of swabs (1 - 2 swabs) without compromising recovery, can be regarded as representative for bigger areas, and with the usual limits of contamination harbors a quantity of analyte detectable by standard analytical methods. Take into account that equally usual are areas of 25 cm² (which stems from microbiological sampling with RODAC plates, and initially had nothing to do with chemical cleaning validation). Also, it is perfectly possible to enhance the sampled area to get more analyte in the sample, when the LOQ of the analytical method is somewhat high. This is especially the case when sampling by rinsing, where the sampled area is usually determined by the surface of the sampled piece and not by an upfront determination, and where the amount of solvent needed to rinse may dilute the sample to levels the analytical method cannot handle.

Best regards