Chromatography Forum

Hi there.
I recently replaced an inlet glass liner, that I broke trying to resolve i different problem (When it rains it pours). The other problem resolved a new one arose. After the replacement, when running under the same conditions i have a loss of resolution. Notice specifically the first peak which is a methane peak 1% balance He, is significantly tailing. The conditions are the same. No clue what's going on, though it obviously seems like more of the sample gas is being injected into the GC.

Thank you guys for your help

The conditions
1.1 ml/min carrier gas flow
50C -7 min - 15 Cel/Min -- 190 - dwell 4 min

Things I've tried:
1)Cut a foot off the column
2)Replaced Liner
3)Replaced gold seal and washer
4)Cleaned inlet with air and methanol after taking it apart
5)Replace septum at top of injector

Here are the chromatograms,

When replacing the liner, did you cut of a piece of the column?
Maybe when inserting the liner you broke a part of the column?

Was the old liner silanized? How about the new one?

Worst possibility - method was developed on GC w/ really nasty, dirty old liner so that it played an important part in acheiving the separation. Having broken that, you won't be able to reproduce the chromatography.

If it's just a case of needing to clean up the new liner, you should be fine - otherwise, you may benefit from the above suggestion (check your column/liner connection, column inlet etc.).

Thanks for the quick response!!

When replacing the liner, did you cut of a piece of the column?

- - I cut the ends of the column off, made sure they were straight, maybe about two millimeters off, just to get rid of any junk that might have been there.

Maybe when inserting the liner you broke a part of the column?

--I don't think this is case, I had already tightened the column in place.

Was the old liner silanized? How about the new one?

-- Tell you the truth, I don't know if the old liner was silanized, it was there when i got the GC which was used by others in our lab. It had some quartz wool which i don't know if it was salinized either. The new one i got from agilent is silanized.

-- I find it interesting that a dirty old liner could have such a beneficial affect on my chromotagrams. It does look like there is a considerably higher amount of sample entering the column. My line of thought is to change the 1ml sample loop and inject less sample.

Thanks again

- - I cut the ends of the column off, made sure they were straight, maybe about two millimeters off, just to get rid of any junk that might have been there.

Maybe when inserting the liner you broke a part of the column?
--I don't think this is case, I had already tightened the column in place.

I suspect that you have inadvertently changed the split or septum purge ratios. Perhaps by not screwing the injector top ( not septum cap ) down completely?.

I'd also be surprised if cutting 2mm from the front of the column is much use, I usually cut about 15-20 mm off the column - especially with easily-friable ferrules.

Also, I always reinstall the column AFTER replacing the liner, just to ensure that the liner doesn't cause the column to break/crack at the ferrule.

Please keep having fun,

Bruce Hamilton

Did you break the old glass liner when it was still in the injection port? If so, did you make sure all the fragments were removed from the injection port?

I broke the old liner at the top when pulling it out with tweezers. I took apart the inlet apparatus a few times so i don't think there are any fragments left over. I will check again, though, do you think a fragment would cause tailing like i am seeing?

At first pass, it would appear that your column flow is slower than previously (or a leak is present). Have you verified the linear velocity from historic. Your methane peak is significantly later than it was prior.

If your compounds are short hydrocarbons, I would be surprised if you are having a problem with active sites.

Greg

Thanks greg,
If you notice, the methane peaks begin to elute at the same time, but since one is so broad the program i'm using gives it a different retention time. The He flow to the column is set by a MFC and has not been toyed with. It is possible there is a leak somewhere in the inlet, I'm guessing that would mean replacing the inlet port completely?
AD

I broke the old liner at the top when pulling it out with tweezers. I took apart the inlet apparatus a few times so i don't think there are any fragments left over. I will check again, though, do you think a fragment would cause tailing like i am seeing?

How much did you take apart? Did you replace the gold seal and washer? Maybe a piece of broken liner gouged the seal, or the new liner doesn't mate up to the gold seal as well as the old liner did, causing a leak.

I usually replace the gold seal every 2/3 liner changes.

Schmitty, have you ever tried the seals Restek sell with the Vespel sealing rings? Its a great idea in theory, I'm looking for somebody who has actually tried them.

Nope, I stick the gold ones from Agilent. I will use a stainless one if my supplies of gold are out, however.

Just ordered some gold seals.
Thanks

Just ordered some gold seals.
Thanks

Did the one that was in there look beat up/scratched/dirty? Could you tell if there were multiple "rings" imprinted on it from different liners?

There was one circular line on the gold seal. No scratches. It looked fairly clean.
Thanks.