LC/MS noise troubleshooting

[mjlindqu]

I recently started work on an Agilent ion trap LC/MS and I'm having trouble reducing the noise on my TIC. I am getting background levels of at least 10^7 in positive ion electrospray. I am using LC/MS grade solvents. I have checked the needle position, cleaned the spray chamber, and bypassed the column to ensure no column bleed. The LC method is run with 90% acetonitrile on an amino column at 1 mL/min. I have also tried splitting the flow. Is there anything else I can do?

[sassman]

Random noise or do you actually have some masses that show consistently? If there are consistent masses present in the noise, then it must be coming from somewhere. You should first eliminate every part of the LC system where it could be coming from. If that does not help, then you should try cleaning the ion optics and ion trap.

[Kostas Petritis]

I would check the background by only infusing a water:methanol:formic acid mixture, then by only using the LC mobile phase and lastly with the column on. There are some amino columns that bleed so that might be the source of the background noise. Do you have the background elimination kit in place for your Agilent ion-trap? If not you may just see polydimethylcyclosiloxanes (mz at 445, 519, 593, 667 etc -74 difference-)...