Thanks for your reply Edmund.
I agree with you that I might have not chosen the right standards for my
sample. In fact, XRD analysis have confirmed that Ferrite is the main form
of Fe in my sample but I did not have any ferrite standards during XANES
analysis. Was wondering if you happen to have any Ferrite XANES spectra by
any chance?
Thanks and kind regards.
Teck Kwang
On 9 August 2013 16:53, 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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-- Teck Kwang Choo PhD Student Department of Chemical Engineering Room 225, Building 36 Monash University Mobile No.: 04-11489904