[N.Ptschelinzew]

Trying to follow the protocol in ISO 8573-2, section C for FTIR analysis of oil captured on a glass sampling disk and the metal body of an isokinetic probe. Everything works great, oil shows up at 2957 and 2926 cm-1 just as expected, BUT
1)   We can not remove the trace oil from the probe body. Even with no oil added to the system we detect more oil than allowed (we have tried ultrasonic cleaning, steam cleaning, multiple solvent baths, etc.)
2)   When we use the industrial grade of the required spectroscopy solvent (tetrachlorethylene or PCE) we end up with a contaminate signal that obscures the area of interest and is also proving extremely difficult to remove (ultrasonic cleaning with acetone, hot soap and water, spectroscopy grade PCE, etc.)
The contaminate signal is at 2967, 2940, and 2912 cm-1 .
Does anyone have any suggestions on how to properly clean metal and ceramic parts to remove an aliphatic hydrocarbon to less than 0.00006 mg/ml ?

[Corribus]

Unfortunately, acetone, soap, polymer debris, dust, virtually anything with a carbon attached to a hydrogen is going to have an absorption resonance in this region. This is why tetrachloroethylene is used... how pure is it? If there are any residual hydrocarbons in it, dissolved polymer, etc, that could account for your contamination.