both negative and positive peak in my chrom

[julietinmay]

I am doing method development for chloride leucine and lactate. the column is metro sep anion dual 2. My condition is 4mM NaHCO3 and 0.4mM Na2CO3 without suppressor. Right now the leucine and lactate peak are positive but choride peak is negative, how can I make them all positive?

[tom jupille]

Actually, the cloride peak is positive and the other two are negative. Chloride has a higher equivalent conductance than does bicarbonate, while leucine and lactate have lower equivalent conductances. In ion chromatography, the polarity of the signal is flipped as necessary to make the peaks go in the "proper" direction.

The only thing you can do with this system is to reverse the polarity while the chloride peak is eluting.

The alternative is re-develop a system using a buffer system whose equivalent conductance is lower than those of leucine and lactate (p-hydroxybenzoate, for example). Then all of the peaks will go the same way.

[julietinmay]

thank you very much, Tom. Is suppressor will make any difference, since the paper I read with the similar condition, their peaks are all positive with suppressor.

[tom jupille]

Yes, the suppressor will make a difference. It replaces the sodium counterions with hydronium. That converts bicarbonate to carbonic acid, which has a very low equivalent conductance.

[julietinmay]

Maybe I should buy a suppressor, is that expensive? Our HPLC is waters, where can I find one?
Thank you very much.

[tom jupille]

Dionex, Metrohm, or Grace/Alltech would be three possibilities.

[Markus Laeubli, Metrohm]

Without having experience analysing leucine with IC, I doubt whether you will see leucine sensitively after suppression as it will be converted into the zwitterionic form which most probably shows only little conductivity. Therefore non-suppressed might be the better solution.