I think it realy depends on what you want to analyze. For example the methods I know for extracting acid-soluble metabolites from plants normaly use 10-20 % TCA, propably for enzyme-quenching reasons.

This is also the biggest difference, I think, depending on what you want to analyze, you should aim for 5 % TCA and higher for proper quenching.

Kind regards

Henryk Straube Henryk Straube I am extracting hydrogen peroxide and assaying its content with xyleniol orange. 5% extract gives notably higher values compared to 0.1% TCA extract ... so my question was does 5% TCA extract has different metabolites profile? ... thanks

I am not sure whether I get your question right, but a higher concentration of TCA could lead to better cell-rupture. It should not effect the composition of the metabolome.

I am also not familiar with your assay, but it seems as if it is pH depent, so higher ratios of TCA in your sample lead to a lower pH and could affect the outcomes.

Henryk Straube the leaf material was frozen and finally ground in liquid nitrogen so I think even 0.1% TCA would have a good cell rupture. Xylenol orange assay mixture is acidic but may be 5% makes pH even lower and affect colour intensity. do you know how much pH value of 0.1% and 5% TCA?

Thanks