The criterion "free of oil and grease" is often regulated by a gravimetric limit value. In this case, either the entire component or only individual function-critical areas can be of importance. Accordingly, immersion baths, spraying bottles or even swabs and wipes can be used to sample the surfaces relevant for testing. Ethanol, a cyclohexane/isopropanol mixture (85/15 % v/v), Novec 7100 or even water is often used as extraction medium. By using an organic solvent and water on two separate components, oils and salts can be differentiated. The extract obtained is then filtered to separate insoluble components (particles). Finally, the solvent is evaporated, and the resulting non-evaporable residues are weighed and the resulting residue masses are calculated relative to the component surface.