UPLC MS and Waters XBridge Shield RP18 3.5

[areinhar]

Hello everybody!!!

i am a beginner in the LC world and here is my problem...

i measurend twice the same compound leucine enkephalin (LE) which is my ISTD in my study... once (4 weeks ago) LE was coming out after 5.44 mins in my 23 min gradient - today LE is coming out at 5.28 mins

i am using Mobile phase A Water:Acetonitrile (95:5 v/v) with 0.1% AA and Mobile phase B 100% Methanol with 0.1% AA

the only thing that changes between the two measurements is that i had to do again my solevnt A and B

is there any trick to make my LE coming out again near 5.44 min

thanks a lot for you help

Alain

[Kostas Petritis]

A lot might had contributed to the retention time change (which is not very significant). It might had been changes in your mobile phases, loss of some bonding of your column, somewhat higher temperatures in your lab (if you do not control the column temperature) etc...

You can try to make your mobile phase again just to make sure that this was not the reason or use a new column but I wouldn't try to "force" the retention time to go back to 5.44 min by other means...