Low Sensitivity in LC/MS due to High Background

I have an Agilent LC/MS Ulitvo TripleQuad and overnight it seems as if I have lost complete signal of my peaks. Sensitivity has dramatically fallen. A technician confirmed that our MS was fine and that the background was extremely high when just running normal water and methanol (MS grade) through the instrument. They are hypothesizing that there might be salt build up throughout the instrument. I normally run my method on a gradient of 10mM Ammonium Acetate in UPW (Mobile Phase A) and 10mM Ammonium Acetate in MeOH (Mobile Phase B). All solvents used are MS grade and run on ESI + mode.
I have tried flushing the system but still see the high background. Does anyone have a suggestion for flushing out Ammonium Acetate or reducing high background in LC/MS?
Or any possible hypothesis for what the underlying issue could be? It seems to have dropped ins sensitivity overnight. I would think the signal would slowly get worse if there was a buildup of salts overtime.
Thanks in Advance!
  • HI Katie, 

    Would you be able to upload a screenshot of the contamination you're seeing? Or list the contaminant ions? 

    I regularly run 20mM and occasionally 200mM ammonium acetate into my QTOF for years and I do minimal cleaning so I don't think that is the source of contamination unless it was a poor grade.  

    A good general cleaning solvent is 50% IPA:Water + 1-2% acetic acid (I occasionally go higher). I don't flush into the MS though. 

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