Small organic acids, lc/ms/ms, separation and detection limi

[RB]

I’m currently trying to analyse small organic acids. I know it has been discussed quite a bit already. However I haven’t been able to solve my problems by looking in this forum or searching the literature. I was thinking maybe some of you guys could help?

A brief introduction:
I would like to analyse (detect and quantify) 7 of the acids in the citric acid cycle (krebs cycle/tricarboxylic acid cycle)
So far I have been able to separate them quite well including citric acid and isocitric acid. In order to separate the last two, I used water (0.1% formic acid). Monitoring in negative ion mode I don’t obtain high sensitivity though. I believe this is a question of pH. However adjusting to a less acidic or neutral pH I’m unable to separate the citric acid and the isocitric acid.

For your information I’m using the following lc/ms/ms system:
‘Waters 2695’ separation module with a ‘Waters micromass Quatromicro™ API ‘ mass spectrometry system.

Regarding the problem (challenge?) with sensitivity:
In the following article “J. Agric. Food Chem, 2007, 55, 551-560â€

[mardexis]

Hi Rune,

What column are you using? Do you have MRM methods? I know your fragments are small but it ought to help.

Marc

[RB]

Hi Marc
I’m currently using a Discovery HS F5 column. Size 100mm x 2.1mm, 5um. I have other columns in house but I’m ready to buy whatever column needed to solve my problem.

I do have MRM methods.
I know the fragments are small but I have succeeded finding 2 good daughter ions for all (except pyruvic acid).
Thanks,
/Rune