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- Posts: 1
- Joined: Wed Apr 07, 2021 7:35 am
I am working on a pesticides method using GC-MS/MS. It's an Agilent 7890 GC coupled to a Waters APCI MS/MS.
A month ago we installed a backflush and since then, I see noise before early eluting compounds. This seems to be at random. Yesterday I injected the same standard 5 times, the second injection shows noise and the other four did not.
I see this noise in both quantifier MRM and qualifier MRM (as can be seen in the picture below), so I think this is the target compound eluting just before the actual peak.
These are the inlet settings:
Injector: MMI using Solvent Vent method
Injection volume: 4 µl acetonitrile
Inlet temp: 80 °C, after 0.13 min to 310 °C ramp 750 °C/min
Inlet pressure: 18.7 psi
Liner: Restek Topaz single tapered liner with deactivated glasswool (925 µl)
Ventflow: 100 ml/min
Ventpressure: 2.5 psi
Vent time: 0.12 min
Column 1 (inlet to EPC): DB-5MS, 5 meter, flow 1.8 ml/min
Column 2 (EPC to MS): DB-5MS, 25 meter, flow 2.0 ml/min
Oven start temp: 75 °C
Maybe someone has any idea what could go wrong?
I tried to insert some images:
https://imgshare.io/image/1.p7rvzj
https://imgshare.io/image/2.p7rhlw