Dear colleagues,

I´ve one question regarding MS noise spectra in LC-MS.

Actually, I am getting spectral (background noise?) peaks in both blank and water (-ve control) HPLC runs on Agilent´s 1260 Infinity II Analytic LC-MS system. These peaks always come with m/z of 255.3, 356.3, and 509.4 at RT of 18.6 and 19.7 min when I used a 27min gradient [gradient of 0-100% B (Acetonitrile + 0.1% Formic acid)] (see the picture of MSD TIC & the gradient). They also appear when I run my actual samples (samples dissolved in water) at a similar Retention time (RT).

I also see them at a smaller gradient of 10min, even at different flow rates (0.4, 0.75, 1.0 ml/min) and injection volumes (1, 5, 10 µL) with freshly prepared solvents. Flushing the HPLC (C18) column with methanol didn´t help. The pH of the mobile phases is 2-3.

Does anyone know what could be the reason for these noise spectral peaks from blank/water control?

I would appreciate your valuable suggestions to fix this troubleshooting & find a possible way to get no background noise in MS spectra with blank/water run.

Thank you very much in advance.