Chromatography Forum

Hello,

I have to analyze a base with an impurity which is a base also.

Sometimes, the base is tailing very intensive and I can use the column only for about 50 injections and then the SST fails.

On the same instrument as I perform this analysis, also the parabens of a zinc containing cream are determined.

Thus, I thought that eventually zinc ions might be left back in the system and I intend to try a rinsing with a chelating agent.

I am not sure whether there are better possibilities than EDTA. Could you recommend one? And which concentration should I use?

Thank you very much.

Florian

You could also use phosphate or acetylacetone (below 100 mM perhaps?) Check first the compatibility of your column.

Dear Carlo,

thank you for you reply; I will try it.

Florian

if you are using regular RP column and any ions in the mobile phase, Zinc ions are not accumulating anywhere. The only way they can stuck to the column is if you run pH above 5 and it is trapped by silanols, but if you have any significant amount of buffer even this is not happening. There is a chance that something else from the cream is trapped on the column. Zinc should not cause any problem for basic compound, unless compounds has several basic and several acidic groups and can chelate.

If you molecule is hydrophobic enough yo can use mixed-mode in reversed-phase cation-exclusion mode and you would not see any tailing associated with silanols or anything esle.