[Ifeffit] Linear Combination Fitting using ATHENA

[Edmund Welter]

Dear Teck Kwang Choo,

it is the ratio of the number of (in your case) iron atoms. This ratio
has no unit. You will therefore get the same number if you calculate
molar % ratio or weight % (Except you consider the weight of the missing
electron in Fe3+... :-). Now, if you weigh your standards and want to
calculate the "number of Fe atoms" you have to consider the weight of
the oxygen. That means, the ratio you get from LCF fitting of your XAS
spectra is NOT the ratio between mol of FeO and Fe2O3, but mol FeII+ to
mol FeIII+! However, if necessary or usefull you can always calculate
the latter from the FeII/FeIII ratio using the molar weights.

So, as a chemist I would say, stay consequently with the molar ratio and
you are on the safe side. You can always multiply the number of mol with
the molar weight, but you would only make things more complicated and
end up with the same ratio or, after multiplying with 100, percentage.

Concerning the deviation between your result and your expectation: I
would be more nervous about the choice of reference substances. If you
only use FeO and Fe2O3 your result is only "correct" if your sample
contains no other Fe component than these two. If it contains
significant amounts of any other Fe component (even other oxides) you
would better not draw any important conclusions from the result of your
analysis.

Best regards
Edmund Welter



On 09.08.2013 05:37, Teck Kwang Choo wrote:
> Hello,
>
> I have been using ATHENA to perform Linear Combination Fitting (LCF)
> on my XANES spectrum to quantify the amounts of Fe (II) and Fe (III)
> in my samples using only FeO and Fe2O3 as standards. The results
> showed a majority of Fe (II), which is contrary to what was expected.
>
> This made me wonder if the LCF results from XANES is a molar
> percentage (mol %) or weight percentage (wt%).
>
> Could anyone enlighten me on this matter?
>
> Thanks!
>
> -- 
> Teck Kwang Choo
> PhD Student
> Department of Chemical Engineering
> Room 225, Building 36
> Monash University
> Mobile No.: 04-11489904
>
>
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