74 mass

[meillid]

Hi, all: I have new questions.

I try to detect a mass 435 (triamcinolone acetonide) using API 2000 (lc/ms) with a concentration of 0.5mg/ml. I believe it is very high concentration (it is my stock solution), I couldn't get a signal with column (the method have been working on an LC/UV). Without column , I can get a signal(Q1 scan), but the 435 is very weak, there is a very strong 508. my question is what may be 508? what the 74 mass difference may mean?

My purpose for this project is to identify a unknown derived from this standard at a concentration of 0.005%(w/w). Is it possible for API 2000 since it is so difficult even for the standard?

Thanks a million for any thoughs!

[Ary]

A few more details are needed here. The mass difference is actually 73 not 74 too. What else is in there? ie what solvents etc. Assuming you havent made a mistake with the masses a change from odd to even mass means the addition of a nitrogen, the usual suspect being acetonitrile though that still doesnt explain the residual difference (32 again the usual suspect is methanol) but this just strikes me as coincidence. Do you run the same eluent when infusing/doing loop injections as the composition the compound normally elutes in?