Attached is a .pdf showing the combined mass spectrum (ESI-) for the free fatty acid region of a chromatogram for a Bligh-Dyer lipid extract. I can identify each peak in the spectrum....EXCEPT the peak at m/z 299. Notably the 299 peak chromatographs very early (C8 column; chromatogram not shown) and is therefore much more polar than say 16:0 or 18:0 or 18:1 etc. In fact, it chromatographs right in between 14:0 and 16:1 (basically co-elutes w/ 16:1). I've thought about hydroxy-18:0, but not big fan of that explanation since if 18:0 can be OH'd, why not 16:0 which is obviously the dominant FA in the spectrum. Since no peak at 271, this means there isn't any hydroxy-16:0. Any ideas?
Mr. Symes,
It can be all compound accounting fo rthe fact that you show only a value m/z 299.
Yes, i've considered hydroxy-stearic (see original post). It is certainly a possibility. But now i'm wondering about 301 and 303....as Noel points out, these two peaks don't match m/z for any known hydroxlated fatty acid. I *thought* i knew what 301 and 303 were - they match 20:4 and 20:5 - but those assignments can't be correct as I ran some standards and retention times don't match. Hmmm....what could these be? I should mention for clarity that these are bacterial (gram-negative) lipid extracts run on LC-MS.
Hi Symes,
First of all I would like to make sure that, in which mode (+ve or -ve) did you run for LC-MS ? if it is positive then Mol. wt. would be 298 (+ve mode) and the expected compound should be Nonadecylic acid, if it is negative mode then it is something other such as (Mol wt. such as 300, 301 or 302) Docosadienoic acid and if you think this your calculated mass (299), then it will be Pentadecylic acid. Most of the crude extract contain quercetin (Mol. wt. 302), so why do not you go for this compounds rather than fatty acid? Hope it will help you a little bit...
Dear: Davies,
I am agree with your statement but we know that sometimes, u can not get exact mass as a pure compound, it might be approximately near to that, So. If you are not getting compound as you expected , then you should have to try with other molecular wt. or compounds, which are approximately closed to their mass.
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