Detection of oil residues on surfaces by swab or fluorescence?

Hello everyone,

I'm looking for a way to evaluate whether a surface or packaging material might have oil residues. The food grade oil on our packaging equipment fluoresces, so I can look for large spills that way, but I'd like to be able to swab a surface or a PET preform and confirm that it is free from oil residues. Is there anything like that out there technology-wise? Looking to detect trace amounts beyond "it's oily to the touch".

ATP swabbing should be sufficient, if you are speaking of animal or plant-based oils, assuming they contain protein(s).  Perhaps establish a baseline positive control first by swabbing an area you know is coated in the oil, to ensure that the oil will be detected by your ATP swab system?

I'm curious about this too. What food grade oil do you use? We use petrogel, and ATP testing does not pick it up.