Iron (III) Chloride in Ubidecarenone Sample Solutions

[syx]

Dear Members,
When I read USP monograph for ubidecarenone capsules, I found FeCl3 solution is added to the sample solution but not to the standard solution. Could anyone give me explanation for the function of FeCl3 in this solution?

Best regards,
SYX

[sarex]

Ubidecarenone assays often involve oxidised and reduced forms of Ubidecarenone. FeCl3 is probably acting as an oxidant in the USP method.
I am not sure why you would not treat the standard in the same way though.

Sarex

[syx]

I do not find the instruction to add FeCl3 solution to the standard solution in the monograph… You fell it is weird enough, don’t you?