poor sensitivity in LC/MS

[jameslizh]

I have one Agilent LC/MSD Trap XCT Plus. Recently the sensitivity is pretty poor (in regular ESI mode), for most compounds, the lowest concentration I can reach is ~100ng/ml or even higher. It should work at least ~1ng/ml. Any ideas to result in this? I clean the ESI glass capillary (it looks like not dirty when I take it out), no improvement. Not sure if there are some hardware problems involved. Thanks.

[Kostas Petritis]

Maybe your electron multiplier is dying?

I recently clean ours until the octapole but it seems that there is no much passing the first orifice before the octapole (it looked pretty clean). The orrifice itself before the octapole was not clean...

How about the vaccum? About the same as always or a little bit higher vaccum (i.e. lower pressure)?

[bykling]

Are you sure that the trap itself and the ion optics are clean? e.g. when you have a power loss and the ballast port on your rough pump is open oil can be sucked back into the system. Therefore keep it fully closed all the time and open it every two weeks for a few minutes. Beside that the nebulizer has a huge effect. Check it with a magnifier.

Regards,
Bykling