Standard addition

[grzesiek]

This is not my field but this article seems interesting:
Simultaneous determination of ascorbyl palmitate and nine phenolic antioxidants in vegetable oils and edible fats by HPLC
Journal of the American Oil Chemists' Society Volume: 80, Issue: 2, February 2003, pp. 115 - 118
Perrin, Christian; Meyer, Liliane

I can touch a bit more about the response curves but would have to see raw data, but sure for now you have other problems to think of

Maybe some chemometrics could be useful (PCR) at t=0, but that is a question for someone who know this stuff better

[CSV]

Yes, of course it's an antioxidant!

The problem is not that ACP degrades during analysis, but that it degrades in the product. In the mentioned product it is 10-50% of label and I want to know what the content was at the time of manufacturing (0% degraded). In other words I want to be able to show that the right amount of ACP was added during manufacturing. Since about half the amount is degraded to several products I'm not able to do this by analysing the ACP itself.

Regards
CSV

[Peter Apps]

There is no way to distinguish fatty acid that was once part of an ester from fatty acid that has been free all along (so you have an irresolvable interference in the analysis). Therefore the only circumstances under which this analysis is possible is the original content of ester being such a high fraction of all other sources of free acid that its measured contribution to the total free acid is significantly larger than the variation in the total free acid.

On in other words how much antioxidant is in the formulation, and how does this compare to the original free acid ?

Peter

[HW Mueller]

Hopefully, we know all the relevant facts by now. If we do and you don´t know how much palmitate was in the sample before asc.-palmitate was added there is no way to find out what you want via palmitate analysis. If you don´t have any idea how much or to what products ascorbic acid degraded you can not use the analysis of ascorbic + asc.-palmitate either. The only possibility I see is that you get a sample immediatly after manufacture, stop the hydrolysis and ananlyze for asc.-palmitate + asc.

[Alex Buske]

[quote] If we do and you don´t know how much palmitate was in the sample before asc.-palmitate was added there is no way to find out what you want via palmitate analysis.[/quote]

I don't think that's true. Isotop analysis could work, depending on the palmitate sources. It's just a little bit more expensive.

Btw: Is there any way to reduce dihydroascorbic acid back to ascorbic acid?

Alex

[HW Mueller]

Isotope analysis in a Mixture of different sources?

A lot of reducing agents (thiols, etc.) will convert dehydroasc. to asc. That´s not the problem, rather the high instability of dehydro is the culprit here, it will give gulonic acid, etc., etc., quite quickly. Those can not be reverted to asc. Also, I have seen good chemists bite out their teeth on trying to figure out how this degradation goes.