We have an Agilent multimode source (APCI-ES, 6120b) on our HPLC/MS. Hadn't used the system in a while and we are currently experiencing a complete flatline when running samples in ES mode (both negative and positive), but we get a signal with APCI. We can tune in both modes and see the peaks/signals but when running a sample, it's a complete flatline with no noise whatsoever... Any idea what we should be checking?
