Chromatography Forum

I recently had to replace the MS fan, which I did and it worked but afterwards the system tunes were showing a high abundance (100) of mass 69. The manual said this was characteristic of pump fluid and I did notice splashes in the chamber before so I had to turn it off and open it up again to clean it. But after that I just can't get it to pump down for some reason. With the column connected it would only get to around ~2000mTorr. I tried connecting a column nut with a no hole ferrule installed and it only just gets below 300mTorr for a short while before climbing back above it. I've tried cleaning the door seal and and replacing the vent valve o-ring, and I also applied some high-vac grease to them.

One thing worth mentioning is when I turned off the MS to replace the fan I forgot to vent. Which I know can hurt the pump but as mentioned I was able to pump it down after that and was able to do tunes and use the instrument. The next time I shut it down to clean the oil I did the venting procedure first, so I find it strange that the pump would work once then not work after that.

Another thing worth mentioning is the diff pump fluid seems to be low too, although the mark has mostly rubbed off it seems to either be at the low mark or below it. Could that possibly have anything to do with it?

Some questions:
1- MS fan?....MS fan or Diffusion pump fan?....are the rotation of the fan is ok? air must be push on the diffusion pump heater
2- Check if Diffusion pump heater is operationnal?
3- Door seal....withdraw it, apply vaccum grease and reinstall it

One thing to be wary of is if someone left the rear retaining screw for the side plate inserted. If it was tightened down you probably would not be able to open the analyzer but if it was slightly threaded in and you open the door it can bend that corner of the plate and cause it to leak.

We have also had one instrument where the interface broke just behind the column nut and we couldn't find it until it broke completely off when trying to remove the nut.

The diffusion pump itself rarely backstreams unless you break vacuum at the roughing pump or outlet of the diffusion pump. They are designed to handle a sudden power outage without backstreaming into the analyzer chamber, but you will often see a few droplets near the pump entrance in the chamber. As for the level marks, I can't remember if there is only a level mark for when the fluid is hot, or if there are two, one for hot and one for cold. If it is at least 1/4 of the way up the glass when hot then it is ok.

Depending on the age of the instrument, there were also problems with the seal around the sight window of the diffusion pump leaking. This was in a service bulletin I believe. Newer ones don't have that problem.

As for mass 69 being high, if the calibration gas valve is open, that is one of the major peaks of the PFTBA and should be near 100% on a standard autotune. If you are tuning for BFB or DFTPP then it will be 100% and 219 should be in the 30-70% range.