Oxidation on SPE

[Mattias]

After giving up on the derivatisation of my peptide (other thread in this forum), I tried to concentrate the solution with SPE (Oasis-MCX).

To my surprise the peptide was oxidised after the SPE treatment. Does anyone know if there are oxidants in the SPE material??

Thanks!

[HW Mueller]

O2 + maybe metal catalysts.

[Mattias]

Thanks,

Maybe a good rinse with EDTA could help? I will test to see if it helps.

I doubt that O2 alone will cause the problem, havn't seen it so far with the stronger solutions.

[Uwe Neue]

No there is no oxidant in the Oasis MCX. If indeed you get oxidation, I would look for another source.

[Mark Tracy]

Cysteine can oxidize in air at mildly alkaline pH. By any chance, are you sucking the cartridge dry at some stage in the prep? Keep the pH moderately acid or add an anti-oxidant like dithiothreitol.

[Mattias]

That could be the case! I was drying the cartridge before the elution step to avoid dilution of the sample.

I'll lower the pH first and see what happens.


I tried a "home-made" SPE also, by doing several injections of the sample with water as mobile phase, before increasing the acetonitrile content and eluting it to the detector. It should work in principle but I got split peaks. Maybe that could work if I use a "stronger" reversed phase column (as Hypercarb)? It is always nice to keep it automated!