Our system: Waters Acquity UPLC coupled to Xevo TQ-S MS/MS detector
Mobile Phase: MeOH/Water gradient with 0.1% formic acid and 10mM Ammonium Formate buffer
Column: Waters Atlantis HSS T3 and Waters XBridge BEH C18 for backup/additional confirmation
Inject: 4uL of a 0.25g/mL extracted sample in MeOH/Formic/Acetonitrile (modified QuEChERS), samples consist of various fruits and vegetables, but we are starting a new study for salmon :|
Pesticide Screen: 140 pesticides, 2 transitions each
Calibration: 4 points (1x, 2x, 5x, 10x LOD), origin ignored, 1/x weight, concentration range varies depending on pesticide sensitivity (lowest is 1ppb (Bupirimate, Carbendazim, Fluridone, Triazphos... to name a few) and highest is 100ppb (Pendimethalin, Pyrimethanil))

For those with a similar setup/application, what are the typical maintenance protocols you follow? I have been cleaning the cone assembly almost weekly, but I still have poor sensitivity so I clean the Ion Block - which is visibly dirty - and sensitivity improves slightly, but not back to where it was right after PM by service engineer. Am i overloading the system because my calibration standards too high? Injection volume too large? Sample concentration too high? Any thoughts/comments/suggestions welcomed on this!!

I am working on validating the LOD for all compounds in this screen, as some are definitely not true LODs - SNR of >1000 for 1xLOQ standard!?!?! :shock: Any tips for me as I work on this?

Thank you for your time!

fyi - we also analyze these samples using GC-QQQ but maintenance protocols are established as it has been in use longer, LC-MS/MS is newer and no protocols established as of yet....hopefully soon this will change!