For aerospace, medical, electronic, pharmaceutical, and other critical applications, direct surface analysis is not always informative or feasible. To validate cleaning, you must design and justify an appropriate extraction protocol. This involves selecting the correct extraction chemical(s) and the correct extraction techniques.

EXTRACTION VERSUS CLEANING
Cleaning surfaces and extraction of residue involve similar chemistries and processes; after all, the goal of both is to remove contaminants from the product surface. However, the protocols are often planned and executed by different groups. An extraction agent can be an organic solvent, water, or blend.

In cleaning, the rinse step removes cleaning agent residue. In an extraction process, the extraction agent should not leave a residue that interferes with the analytical method under consideration or, if the part is not sacrificial, with further processing of the product.

The goal of cleaning is to achieve a surface with appropriate qualities. In extraction, we may purposely expose the surface to a potentially damaging chemistry or to a long extraction time, to the extent that a portion of the product is extracted along with the contaminant. This can be a problem particularly with plastics, complex composites, and porous surfaces. However, the desire for enthusiastic extraction must be balanced against the issue of artifactual contamination. Materials extracted from the product may interfere with analytical determination by masking the contaminant. Examples of interference include chromatographic co-elution with contaminants or “swamping out” low levels of the contaminant of interest.