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Hi Natalie,

I have not had your problem but I might be able to help.  Which derivatization method are you using, and which isotope system is your focus?

On the nominally-polar phases like DB1 and DB5 (and equivalents), those two are likely to be elution sequence neighbors.  One very low-effort solution would be to tweak your oven program to improve separation without any hassle.  If you're dating H isotope analysis the best answer is to reduce analyze concentration for a list of reasons too long to explain here (except 'Marilyn says so').

A cheater's way out is to note that Tyr has an hydroxyl group that makes is slightly sketchy as a derivative; prosthetics added during esterification of carboxyl groups also modify hydroxyl moieties but are less chemically stable.  That means, in addition to any fractionation induced by derivatization of the carboxyl, there's an extra one that has to be accounted for during the hydroxyl modification, and there's YET ANOTHER ONE  associated with decomposition.  In other words, it's not the best thing to be measuring anyway.  (The caveat is if you're interested in N isotopes, in which case there's no backdoor excuse to crawl through.)

Please contact me off list if more boring, gory details may be helpful.

-patrick

Indiana University
Department of Earth and Atmospheric Sciences
1001 East 10th St.
Bloomington IN 47405

On Apr 5, 2017, at 5:08 PM, Natalie Wallsgrove <[log in to unmask]> wrote:

Aloha All, 
I was wondering if anyone else has observed trouble with separation between tyrosine and lysine on newly purchased columns? Our aging column in one of our Trace GCs is starting to show its age, but we've tried several new columns and consistently get bad separation between tyr and lys (all other AAs look fine). We have historically used SGE BPx5 (60m x 0.32mm x 1.0um) columns with success, but we've tried multiple new BPx5 columns as well as an Agilent DB5 (also 60m x 0.32mm x 1.0 um) with the same results. 

Has anyone else had this trouble? The old columns were purchased in 2011/2012, and all the troublesome columns have been purchased since late 2015. 

Thanks! Natalie 

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Isotope Biogeochemistry Laboratory
University of Hawai'i at Mānoa
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