Peak distortion in DB-17MS column

Chromatography Forum: GC Archives: Peak distortion in DB-17MS column
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Hubert on Thursday, October 24, 2002 - 05:44 pm:

Dear all members,

I am wondering if anyone has the experience using DB17MS column. Recently I installed it in my GCMS system and injected the standard solution containing about 30% BSTFA in toluene. The injector was set at 200C. The initial oven temperature was set at 90C. The compounds were some derivatized beta-blocker drugs. I found that peak distortion (not tailing) was observed. Initially I guessed that was the problem of injection of dis-similar solvents and thus I evaporated the BSTFA after derivatization and reconstituted the dry residue with toluene. However, the same pattern still appeared. As such, I tried to install a guard column of about 1.5m and re-inject the derivatized standard (in 'mixed' solvent) and the peak shape resumed normal. I understand that guard column is used here for "space focussing" but I am just queried why the solvent and temperature focussing doesn't work in my first attempt, as toluene is pretty much "like" the stationary phase of the DB17MS column. Is it the column's problem? Please advise.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By BSTFA experience on Friday, October 25, 2002 - 07:48 am:

At my company we derivative with BSTFA routinely, and have published papers detailing some of its applications. However, we never use toluene as solvent, mostly DMF or (2nd choice) pyridine. DB-17 should be fine for this. What do you mean by distortion; if triangular-shaped with slanted front, sounds like overloading. You might want to re-install just the column, at the inlet end, maybe the amount of column protruding through the ferrule is incorrect, or capillary end not perpendicular and straight.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Jason Ellis on Friday, October 25, 2002 - 10:09 am:

Toluene sometimes shows peak shape problems if you have your initial oven temperature too low and you are doing a splitless injection. This is caused essentially by "excessive focusing" on the front of the column. Try doing an injection at 100C initial oven temp instead of 90C. I have had this same problem before, and it was solved by adjusting the initial oven temp to about 100C (only 10C below the bp of the solvent).

See the following reference for greater info on the "excessive focusing" phenomenon:
"Classical Split and Splitless Injection in Capillary GC", 2nd edition, Konrad Grob, Hüthig, 1988, page 158.

Jason Ellis
Tech Support Engineer
Agilent/J&W


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Hubert on Friday, October 25, 2002 - 11:58 pm:

Thank you very much for all your suggestions.


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