Chromatography Forum

Hi
I have a refurbished Agilent GCMS 6890/5975. I am new to GCMS and ran an autotune, but realized I don't know what the various things on the report mean and that I also don't know what normal values are. For example the H2O is at 4%. Where I worked previously, 4% was not good, but I've tried to look for leaks and cannot get the 4% to go down. i tried to bake the oven at 250degC and that also did not do anything for lowering my water %. I do not know what to do so any help would be great. I do not have a transfer line though I did try to lower the temp on Aux 1 to see if that would help. It did not.
thank you for any help you can give me.

How long has the system been pumped down? When open water gets into the system and is slow to dissapate. It should go down over time.
Agilent claims air/water < 10% is fine.
Your Aux 1 temp is the transfer line heater.

The system has been pumped down since Thursday, so a little more than 3 days.

Could you tell me why the H2O value when down to 2% when I lowered the Aux 1 temp? I do not understand that.

Thank you for your comments.

Hi

What is your Nitrogen % when you change the transfer line temp? Also what was the temperature of the GC oven in both instances.

Normally small leaks tend to manifest themselves at lower temperatures ( GC oven and transfer line ), this is due to the graphite/vespel ferrule at the end of the transfer line shrinking with the lower temp. What you are seeing is the the other way around.

Having said that difference between 2 and 4% is not too much, personally I would not worry about it if the nitrogen is low as well.

If it does worry you I suggest trying several times at a lower and upper temp to get some hard data.

I have isolated the leak to the Agilent gasclean system that I bought to filter my He gas that I am running. It seems that the system introduces H2O (4%) and N2 (10%) to the system. with the Agilent GasClean system off my lines I get gas H2O at 0.8% and N2 at 0.6%.

I do not know why the GasClean system introduces so much troublesome gas into my system. Does anyone else know?

thanks for the suggestions.

I don't know much about the Agilent "GasClean" system but most gas traps/sorbents are packed in N2 and sealed for shipping. Usually you want to purge them with He for quite a while before connecting to the GC if they are NEW. Even after purging for a few hours we would still see N2 and H2O at larger than normal levels for a few days.

I would just connect the traps to the He bottle and set the regulator so you can feel a gentle flow of He coming out the end of the lines and through the traps. Leave it like this for a few hours maybe more and then connect it to your GC.

Ty

I took the gasclean system off and replaced it with a labclear filter and the problem went away. thanks.