Peak tailing and drift throughout a run
We've had this problem on and off for a while but every so often two of the analytes we look for start drifting and tailing throughout the course of a run, none of the other compounds are affected - we look for a total of nine steroids in animal urine. At the start of each run the peaks look normal but they gradually become broader and more retained as the run goes on. On average each run is ~120 injections.I have attached two pictures of how the peaks look at the start of the run and how they look at the end.We use a UPLC Acquity system coupled to a Premier mass spectrometer, the mobile phases are 0.1% ammonia in water and 0.1% ammonia in methanol (gradient) and we use an Acquity C18 BEH column (the column we are using now is quite new, only about 500 injections). After each run the column is cleaned by flushing with 50:50 water:methanol.Any thoughts about why this happens and how it can be prevented would be greatly appreciated.