[gilly]

Could someone please clarify for me: I am testing Vitamin A palmitate (retinyl palmitate) by the USP method for multi vitamins. For any of these methods the std is retinyl acetate and a conversion factor of 0.872 is used to convert to it's retinol equivalents. The molar responses of the acetate and palmitate forms are equivalent and all methods say to use the acetate as std. However, the products I am testing state the amount of retinyl palmitate with an equivalent retinol equivalents amount also listed. The difference between these two values is 1RE=1.83 retinyl palmitate. I am a little confused here as saying that you can use the acetate as standard for both forms (acetate and palmitate) would indicate the same conversion factor to the retinol equivalents however it is stated on product labels as this not being the case. I hope this is clear enough. Could someone please help me out.

[JGK]

Retinol mw = 286.45
Retinyl Acetate mw = 328.49
Retinyl palmitate mw = 524.86

The conversion factors are calculated from the molecular weights:

Retinol mw (286.45)/Retinyl Acetate mw (328.49) = 0.872

So X equivalents of Retinyl Acetate is converted to X x 0.872 equivalents of  Retinol.

The result generated by your assay will be in terms of "Retinol" equivalents which you then have to convert to Retinyl Palmitate

Retinyl palmitate (524.86) / Retinol mw (286.45) =1.83


So X equivalents of Retinol is converted to X x 1.83 equivalents of  Retinyl Palmitate.