By Durk on Friday, April 4, 2003 - 05:25 am:
Who has any experience analyzing ascorbic acid in cosmetic products. We now extract with water at 60 °C for 10 minutes. After cooling the extract will be analyzed using capillary electrophoresis. We have problems with stability of the ascorbic acid.
Durk
By Anonymous on Friday, April 4, 2003 - 06:48 am:
It depends of what base your cosmetic products have.
If its an oily base, you can add about 5 ml chloroform, xyleen, THF, ... until the cream has suspend, and then add water and let stirr for a few minutes.
Dont use temperature to dissolve ascorbic acid, but the stability of ascorbic acid will always be a problem unless you use a preservative in the sample and standard solution.
By HW Mueller on Friday, April 4, 2003 - 07:08 am:
Ascorbic is quite stable in acidic (pH 2) solutions if air is the only oxidant present. This may not hold for very small amounts on HPLC columns. I would be very interested to hear about what it does on CEC columns.
By Anonymous on Friday, April 4, 2003 - 09:35 am:
mix sample with sulphuric acid eluent and a suitable solvent to solubilise your sample ...
dilute and inject. As above, ascorbic acid stable in acid conditions. on the link is an application using ion exclusion with direct conductivity detection.
http://www.metrohm.ch/docs/app/notes/pdf/o7.pdf
By Anonymous on Friday, April 4, 2003 - 10:22 am:
as above but you can use UV detection too.
By Fabiano on Thursday, April 10, 2003 - 03:56 am:
Dithiothreitol is used to reduce the dehydroascorbic to ascorbic for total vitamin C activity. It also stabilize the stock solution avoiding the oxidation of the pure standard.
I used in juice analysis, NH2-HPLC, UV @245, RSD of 3.0% between 2 calibration curves, first in the begining and the second in the end of batch(same day).
This conditions are used by NIST for food-matrix Standard Reference Materials analysis.