I am trying to increase the final yield of acetylcholine (ACh) in my biofluid samples. I need to get the yield high enough for high confidence annotation of ACh (currently all I can really say is that I've got something that matches the ACh expected mz).
My first samples were prepared using C18 solid phase extraction using a water liquid phase and methanol to elute. Based on my understanding of C18 SPE, I assume I've lost a lot of ACh at this step, because I assume the positively-charged ACh would have been washed away during the wash step.
Now that I have a polar analyte to target, I need to prepare more samples with a higher ACh concentration. I should be able to increase the concentration by using an SPE protocol more amiable for ACh extraction, but I can't find a protocol like this in the literature. How does one design a targeted SPE protocol? Can I assume any HILIC procedure that targets charged molecules will be appropriate here, or is there more to consider?
My problem is made more complicated because I need the final, concentrated version of my extract to be compatible with my downstream bioassay (i.e. no carry over from acid, no strong solvent that can't be removed)