column bleed GC 7890A

[chromatonoob]

Hi! I don't have a lot of experience with GC maintenance. I just replaced the column and ran a few blanks through it. Blanks look good, but once I ran a standard through it, the baseline doesn't seem to settle.

It's a 60 m column, id: 0.250 mm, film: 0.15 um. DB-23

With a column this long, I'm going to condition it over night. (Whereas prior to this, I conditioned for 3.5 hours at a high temperature.) Hopefully the baseline settles at this point.

Would love any other suggestions? Thank you!

[cleh]

I like to condition my columns without connecting the detector end. Install it in the injector, make sure your flow rate is good, and make sure there are no leaks. Bring the injector up to temp. Heat the oven up to the max temp the column allows (I believe this one is 240) for a few hours (the longer, the better) and then cool it down to your initial temp. Now check to see if the injector ferrule is leaking and tighten it if necessary. Connect the detector end and when leak free, heat the detector to your desired temp. Heat the oven up to max temp again for 10 minutes or so. Cool it back down to your initial temp and make sure the injector and detector ferrules aren't leaking. New ferrules will expand when heated and contract when cooled so this is a break in for them. What you're seeing now may be due to a leak, not bleed. Good luck and please let us know how it goes.

[chromatographer1]

Please remember there are two maximum temperatures for any column.

One is for isothermal analysis. The other is for programed temperatures where the final temperature is not held constant.

Do not subject the column for an extended time at the programmed max temperature, as the expected lifetime of the column will be shortened.

best wishes,

Rod

[Peter Apps]

What are your blanks, and what is in the standard ? When you say that the baseline does not settle, does it rise steadily during a run or is it unstable before the injection ?

When did you last change the inlet liner and septum ?

I would advise against a lot of "conditioning" until other possible causes of baseline drift (if that is indeed what you are seeing) have been eliminated. If you have a leak or dirty carrier gas then holding the column at high temperatures for long periods can only damage it.

Peter

[James_Ball]

I like to condition my columns without connecting the detector end. Install it in the injector, make sure your flow rate is good, and make sure there are no leaks. Bring the injector up to temp. Heat the oven up to the max temp the column allows (I believe this one is 240) for a few hours (the longer, the better) and then cool it down to your initial temp. Now check to see if the injector ferrule is leaking and tighten it if necessary. Connect the detector end and when leak free, heat the detector to your desired temp. Heat the oven up to max temp again for 10 minutes or so. Cool it back down to your initial temp and make sure the injector and detector ferrules aren't leaking. New ferrules will expand when heated and contract when cooled so this is a break in for them. What you're seeing now may be due to a leak, not bleed. Good luck and please let us know how it goes.

For anyone new to doing column maintenance there is a trick here if you are using vespel/graphite ferrules that can save some headaches with this problem. Keep extra ferrules in a small beaker inside the oven(not in their plastic case of course) and the temperature cycling will pre-shrink the ferrules so that when they are used you will get little if any loosening after installation.

[Peter Apps]

Thanks James,

That sounds like a good plan.

Peter