Chromatography Forum

Hello

I have a contamination on my GCMS THERMO DSQII... I'll try to sum up my issues, help appreciated

It began after an important maintenance : MS, foreline pump, column and PTV port injection (I know that it is a lot in the same time but it was quality obligation...)
The first day the tune was allright but at the third injection no more signal...and the MS was very dirty.
After other MS maintenance it was badest, impossible to tune the MS. So I thought the problem came from the GC. Thince thermo came the week before to change the PTV pressure control card (the second in 6 months....) we thought we had a contaminant in the split line... so we decided to use the second SSL port of the GC : signal come back and tune was not too bad (but not the best I ever had).
So I made new qualification injections (to try ) and, again, signal decreased a lot and, in the chromatograms : high baseline and a big and long peak of alkane (especially beetween 10 and 18 minutes on 35 min injection)... so, again, MS maintenance, new column conditionning and SSL injector cleaning...
and today : chromato are even worst...

helium is oK thince others GCMS on the same line are ok.

do you think it could be a contamination from the foreline pump?
If it is that, how can I resolve this?
If not: a glove contamination (new references)?

please help me I'm turning mad

and sorry for my bad english

It is very likely, that the issue is related to the foreline pump.

hello
thank you for your answer.
I think so... What can I do by myself to resolve that?
thanks for your helps

hello

to go back on my problem, do you think that it is possible than a foreline pump contamination can be more important with one of the two lines of the GC (with the PTV line, contamination is so important that it is impossible to tune the MS whereas tune is realizable with the ssl line)

thank a lot for your help

What maintenance did you perform for the foreline pump? Do you have alternative foreline pump in the lab?

If you have a hydrocarbon peak in the chromatogram, the hydrocarbons would have to come through the column - the only way that the forline pump could be involed is for oil to have been transfered from the pump (dirty hands) to inlet parts or GC plumbing - particularly if the peak is repatable from injection to injection. Note other posts about hydrocarbon background on this site (there are many).

Plug off the mass spec and look at the tune profile. Do yo usee hydrocarbon peaks? If, with no column flow in to the MS, you see no hydrocarbon peaks, you do not have hydrocarbon contamination of the mass spec.

While you have the column pulled, it would not be a bad idea to put the end of the column into a small bottle of solvent and look for a stream of bubbles coming from the column (with column flow on) to be sure that you actually have flow through the column. (I assume you ran the k value test on column installation? This should indicate correct column flow - but let's be sure the flow is coming out in the right place!)

Do you have traps between in the gas lines and the back of the GC? If there is hydrocarbon contamination in the gas system, it will break through the traps as they become full - and it will be at a different time for each instrument because it is a function of gas flow through the traps.

If the mass spec checks out as clean, I would suggest you start with a bottle of clean helium, a known good regulator and tubing fresh out of the box (cleaned for GC operation by the vendor) and plumb up the system. You can also take the inlet end of the GC column into an adapter and hook it to the plumbing coming from a regulator. Set the regulator to a pressure as similar a possible to the pressure setting for the inlet when the inlet is close to room temperature. With flow from the gas cylinder through the column you bypass the inlet system - and this can demonstrate a lack of hydrocarbon peaks. Hook up through the inlet and see peaks or hydrocarbon background with thet inlet parts and oven close to to room temperature and you have demonstrated the location of the hydrocarbons. (I've seen this done by a service engineer to demonstrate to a customer that the gas source was indeed contaminated wiht hydrocarbons -- and not from the newly installed instrument. The customer was left with an instrument running off a good bottle of gas and a declining hydrocarbon background as ghe hydrocarbon contamination was allowed to purge from the inlet system.)

I will add - if you try hooking the column up to a regulator, use great care! If you set the pressure too high, you will introduce far more helium into the mass spectrometer than you want. If you are not confident of your abilites to do this, call your service engineer and see if he/she has a better idea.

The fact that you lost the hydrocarbon contamination when you first switched inlets, then it returned, would indicate it is coming from your gas supply. It simply took time for the hydrocarbons to flood into the new inlet when first using it.

Since other instruments run off the same gas supply line but are ok, I would think it is either as Don mentioned a saturated hydrocarbon trap just prior to the instrument or during the maintenance work someone disconnected a gas line and touched it with some of the pump oil on their hands which introduced the hydrocarbons into the gas line.

If there is a hydrocarbon trap(or moisture/oxygen traps) just before the instrument, I would replace that and all the tubing between it and the instrument and see if the contamination goes away. It may take a little time for it to completely flush from the system, but you should start seeing a reduction soon.

Thanks a lot for your help

Column connections not implied: leak Check and Kfactor ok

I did an acquisition without injection : same contamination, So no seringue implied

I try to remoove contaminants from the inlet with different solvants and heat : no decrease...

I looked at the filters : no saturation (color ok) but they are old (3 years!!!)
So I changed them,... Answer tomorrow!

And thermo field engineer come tomorrow to fix the PTV...pressure regulation out of order... I hope hé will help us with the contamination

I Will let you know