Chromatography Forum

I have an old Thermo PolarisQ that up until recently has been a great workhorse. Then, about two weeks ago, during an otherwise normal chromatographic run, the baseline went absolutely flat -- no noise at all.

I've been troubleshooting this system and getting nowhere, so I'd be very much appreciative of any help. Here's what I've done so far:
1. Cleaned the analyzer.
2. Replenished the tune compound.
3. Replaced the source.
4. Replaced the electron multiplier.
5. Dusted the conversion dynode.

Some details:
1. The instrument will not complete an autotune. It passes everything until it gets to the electron multiplier then fails at a multiplier voltage of 2500V with an undefined gain. As I mentioned, it has a new multiplier (but both the new and the old multipliers produce the same result).
2. All diagnostics pass.

Any suggestions on next steps would be very much appreciated!

Regards,

Dave

I am not familiar with this model but from what you describe it sounds like you have a problem either with the high voltage getting to the detector or the signal coming from the detector. If you have a volt meter capable of reading 2500v DC then you can test the power supply at the point where it passes through the analyzer chamber to the detector. You could check the return signal where it passes through also. After the signal leaves the detector it probably (if similar to most other models) will pass through an amp somewhere, which could also be a problem.

Just a few things to check that I can think of.