I've regulary measured sodium ascorbate on a silica based organic acids column (Prevail C18 from Alltech)using 0.08% aqueous formic acid or 25mM phosphate buffer pH 2.5. When I tried this system to analyse ascorbic acid 2-phosphate magnesium salt I go no retention and very poor peak shape. I lowered the pH to about 2 by using 0.1% TFA. I got a better peak shape but still no real retention. Does anyone have any suggestions for getting decent chromatography with this compound?
Thanks
John

The phosphate group has made the analyte more polar and most likely reduced the pK of the acid, requiring a much lower pH to protonate the acid. I would try lowering the pH to 1 or 1.5 and see if it will retain longer. It will require a lot more acid but you should be able to get the pH down that low. The column should be stable down to pH 1. If the analyte does not retain longer, then the compound may just be too polar and need to be separated by some other means such as ion exchange. Of course you could try a longer column if you have not done so allready.

You might want to try an ion pair reagent. Something like tetrabutyl ammonium phosphate or sulfate may help to retain it longer. 0.1% might work.

Thanks a lot for your help I will try what you suggest.
John

Your analyte looks like it would be been separated via anion exchange chromatography. While you can probably accomplish the separation using ion pair, anion exchange will give you much better results for an analyte of this polarity.