Chromatography Forum

I am trying to troubleshoot a problem I faced when analyzing a water solution of bupranolol 15 ng/ml (system suitability test). I had a high signal intensity in the first injection (A=208718630), but in the second (A= 6081794 ) and subsequent injections the intensity dramatically decreased. After 15-16 hours (on the next day) the situation repeated (the first injection gave a high intensity, whereas subsequent injections yielded a much lower intensity).
I was advised to change rotor seals in 10-port valve and 6-port valve (autosampler valve). But now I do not have new rotor seals. I also try to use a ceramic emitter (liquid junction) instead of a stainless emitter but it does not help. I also check the stability of QExactive with the HESI-II source by infusion of calibration solution directly from the syringe pump (direct infusion) at 2 microliter/min for 4 hours. The signal is constant.
Has anyone faced a similar problem? Any suggestions or tips would be appreciated.

The problem was solved by cleaning the ion source (ion transfer capillary, exit lens, S-lens, octopole, etc), quadrupole and C-trap. As I understand, loss of the signal over time was caused by the charging effect. My thanks to Thermo Service for help.