Hi,
Ever since starting work on bile acids using LC-MS, I have seen peaks corresponding to my standards in my blanks. It doesn't appear to be straight forward carry over since a blank after a standard can have similar sized peaks, or sometimes smaller peaks than a blank before the standard! I have tried various combinations such as sampling from the same blank vial or using a series of vials so that the needle only enters each vial once. Recently I have started seeing severe double, triple and unsymmetrical peaks in my blanks and low concentration standards are now also playing up, giving random results unrelated to standard concentraion.
I wondered if my column (C18) has become saturated over time due to the high concentraions of bile acids and my gradient mobile phase is not efficiently removing my compounds after each sample.
mobile phase 30% 5mM amm acetate, 0.012% formic acid in water
70% as above but in methanol
then switching to 5% and 95% of the above respectively, then switching back to 30%/70% at the end of the run.
I'm a complete novice so any suggestions on how to troubleshoot this would be greatly appreciated!
Thanks.