Identification of unknown oil/grease residue by MS..

[Pegry]

Hi everibody,

we have to identify an unknown residue that have contaminated an API. The problem is that we have received only about 1mg of this material extracted and concentrated from the API. The residue seems like oil/grease but we have no idea of what it could be or from where it come..
We have access to a GCMS and a LCMS (both of them single quad) but we have a very low quantity of material.

We think to dissolve it in hexane, inject to GCMS and search in the libraries.
Do you have some experience in the analysis of oils/grease by MS (LCMS)?
Do you have any cue to what we could do in this situation?

Sorry for the long post and thank you in advance for your answer

Bye

[sassman]

By API, do you mean a Sciex API mass spec? What part of the instrument was contaminated? If it was inside the mass spec, you could have had vacuum pump oil get sucked back into the MS due to improper vacuum shutdown. I would analyze by GC/MS and GC/FID. If you get multiple peaks, then it is likely oil.

[cmg1220]

In my experience, grease/oils look like a bunch of peaks together in a generally gaussian shape with similar ion patterns looking like long chain hydrocarbons. Expect this to be a high-boiling/late eluting group of peaks. You want to use a high-temp nonpolar phase for GC/MS, such as a DB5-ht (up to 450 C I think). Get the inlet/ms transfer line up to 350 and do an oven ramp up to 350 with a hold at the end to clean everything off the column (I use 10 minutes). You can maximize your sensitivity by using splitless injection with a tapered inlet liner with a bit of glass wool in the bottom (or even a double-taper). I have used a cyclosplitter liner with good results for dirty trace level samples also. Also try to dilute in as small of a volume as possible. I like to use the 200-microliter glass autosampler vial inserts - you only need a few microliters to inject each time. You're probably right that hexane is a good solvent. Hope that helps.

[krickos]

Hi

Had the same problem a couple of times in relation to API production. Usually or when I think of it, always the oil came from a leakage from stirrers or similar in the production. The oil used should be "food grade approved" and the production deparment should be able to provide you with the oil to confirm your analysis. If this is the case then it is of course much easier to identify and quantify.

Otherwise the general approach cmg1220 mentioned is similar to that I have used.
Though i prefer N-heptane from a Health perspective than hexane, provided resolution does not become a problem.