Need help, splited peak and SDS

[Fabiano]

OK you got me there. My comment was a bit to premature. If you have a well worn amino column with plenty of silanols, it is possible that ascorbic acid elutes. Since you got spectra, was there a difference in the spectrum for both peaks?

This was long time ago at college, but I remember there was a minimal difference between peaks, some 5-10 nm shift at max., If memory don't fail.

[Uwe Neue]

Well, with a mobile phase of straight water or organic solvent without any ions in the mobile phase, one can do some strange things with the right stationary phase. I remember publications by Blasius using crown ethers as the packing. You can separated a series of salts with the same anion, but different cations, or a series of salts with the same cation, but different anions. With other words, if you would inject a solution of sodium chloride and potassium bromide, you could get 4 peaks: sodium chloride, sodium bromide, potassium chloride and potassium bromide.

However, this all goes belly up, when you add a salt to the mobile phase.

I will scratch my head a bit more about your observation, and the possible reason for it.

[HW Mueller]

There is no reason to scratch ones head. It is not possible to separate ascorbic acid from ascorbate, it is not possible to have a different ratio of ascorbic to ascorbate in an identical solvent. It could be possible to have different ratios if the mobile phase in which the two peaks were seen was different, as it could be at tm (to) if coinjected junk came through without retention. Also, if ascorbic was separated from ascorbate the spectra should be more than a few nm apart.

[Peter Apps]

I begin to get a strong sense of deja vu ...
viewtopic.php?t=5549&postdays=0&postord ... s&start=15

Peter

[XL]

Hi zeq,

I was wondering if you had solved the problem. I have been thinking about this puzzle, and here is my suggestion.

The challenge: the analytical column fouling by sample matrix (0.5% SDS)

Possible solution one - use a SCX trap (guard) column before the RP analytical column at pH 3. This way the drug molecule is positively charged and retained by cation-exchange mechanism while the SDS is exluded via electro-static repulsion. You can concentrate the analyte and devert the SDS to the waste before switched in lime with the analytical column. You can replace the trap column periodically.

Possible solution two - probably a strong cation-exchange column only will serve the purpose without a RP column using buffer concentration, pH, and/or organic solvent gradient.