Hello all,

I am looking at small molecules in untargeted analysis of biological tissue with a nano-LC MS/MS system.

My sample extraction procedure is pretty straightforward:
1. homogenise the tissue with ceramic beads in 0.25% acetic acid + anti-protease tablets
2. sonicate 1 minute on ice
3. centrifuge
4. filter supernatant through 3kda molecular-weight cut off filter
4. concentrate filtrate with xcelvap system (nitrogen stream / pressure / 30 C)
5. filter through SPE C18 cartridge (with pre rinsing steps)
6. inject

The final spectra has a repeating plastic polymer that is suppressing the signal of my small molecules of interest. All plastics I use are of high quality (lo-bind eppendorf) and are pre-washed in methanol. I rinse the amicon mwco filters with methanol and then ultrapure water to remove glycerol before use. All reagents are new and contained within glass bottles.

I am not sure how to get around this issue and it has delayed me for months.
Any advice is appreciated. Thanks!