gamma aminobutyric acid (GABA) tailing peak or contamination

[Jen]

Recently purchased Intrada amino column 150x3mm for separation of gamma-aminobutyric aic(GABA) and betaaminobutyric acid by LC/MS/MS. The separation are good. the peak shape of GABA (MRM: 104.1 -->87.1) are tailing badly. however, the internal standard of GABA-d6 (MRM:110->93) peak shape is beautiful. make 0 volume injection, see a big bump at GABA retention time. suspect the bump is part of the tailing peak. Clean MS capillary, all fresh mobile phase, could not solve the problem, could not get ride of the bump. see hugh background at 104.1--> 58.1 also.
mPhaseA : H2O with 1mM Ammonium acetate
mPhase B: MeOH with 1mM ammonium acetate

Is this a Intrada amino column problem?

Any suggestion?

Thanks,

Zhen

[MSCHemist]

I'd do GC/MS by derivatization with methyl, ethyl (I'd recommend), or propyl chloroformate (Phenomenex EZFAAST). Simple, sensitive, less problems than LC/MS. That's what I do for amino acids.

http://www.ncbi.nlm.nih.gov/pubmed/22677651 Here's a link though I disagree with the SPME. I just extract with chloroform and inject.

[Jen]

Thanks for the suggestion.
I am working on a method with 17 compounds including GABA. In order to keep all 17 compounds in one run, I have to derivatize them. I also use ethyl chloroformate (ECF) with pyridine and ethanol. The reaction are simple and react at room temperature. All sixteen compounds match with other lab reference interval. Unfortunately, GABA results is not matching with our GABA -NFPA ion pairing method results. majority of the results are matching, but some are much higher. I can't figuer out why?

What is your GABA reference range? I would love to go back to the ECF derivatization method.

[MSCHemist]

I've never done GABA I do the amino acids (except arginine) and some of the TCA acids (pyruvic, succinic, malic, fumaric, lactic, and citric) in the range of about 10ppm to 500ppm injected (I can go lower on SIM as I occasionally do trace glutamate) and I normally do 10:1 split when I could go splitless for higher sensitivity. Try varying the protocols. Some analytes need a fair ammount of NaOH ( at least 0.1N for glutamate) in the reaction media to prevent or reduce side reactions, others like 0.1N NaHCO3 as in the method of Jia/Qiu, some like two doses of ECF, others prefer minimal water in the reaction media and do best in acetonitrile with a small ammount of pyridine and corresponding alcohol.

Weird you have having issues. With an isotopically labeled standard you should be able to get away with murder analytically as seen with many of those quechers methods.

[Yazawa]

Hi Zhen,

Intrada Amino Acid column require pH and ionic strength gradient under normal phase elution mode.
Please refer to the following application:

http://www.imtakt.com/TecInfo/TI741E.pdf

Regards,

Yazawa