[HarD]

I performed C18 SPE in an untargeted metabolomics study. My aqueous samples were run through the column, followed by a wash step using water, and elution in pure methanol. I was surprised to see a compound with a mz matching acetylcholine when I got my FTICR-MS results back.

My question is two-fold: how probable is it to capture acetylcholine under these conditions, especially given that it is a charged molecule?

I want to follow up on this, but I need to increase my yield of acetylcholine to get the MS/MS spectra. I was wondering how one would go about choosing the best SPE method for acetylcholine. Should I try HILIC? Or maybe I can use the C18 with slightly adjusted conditions? How do you know what column conditions to use to go after a metabolite of interest?

[Babcock_Hall]

Given that this is a quaternary ammonium ion, I am not entirely surprised.  We contemplated using SPE for pyridinium ions, but we did not get around to trying it.  I am not sure of the answer to your other questions, but I did amass a few SPE-related documents from manufacturers.  That might be a good place to start.