Recently, I am experiencing a real problem regarding the high baseline of my quantitative analysis using positive multible reaction monitoring (MRM) detection. The instrument is a brand new API-2000 MS/MS, which was installed in August. I used to have a very low baseline (e.g. 50 - 100 cps), but since early November, I am having a relative high baseline ( 400 - 6000 cps, sometime high, sometime low) using the same acquisition method and of course the same LC method. I thought that the front end might be contaminated and a service engineer from Sciex was called to clean the focusing ring, skimmer, and even the Q0. But the problem is there. Any suggestion for solving this will be genuinely appreciated.
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