Re: [Ifeffit] Normalization of XANES spectra

-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit- bounces@millenia.cars.aps.anl.gov] On Behalf Of Jens Kruse Sent: Wednesday, October 29, 2008 1:31 PM To: ifeffit@millenia.cars.aps.anl.gov Subject: Re: [Ifeffit] Normalization of XANES spectra

Thanks for your replay and sorry for the confusing question. but I

it not getting better.

Scott, you are right LCF would be helpful but even with lot of standards it is hard to get a meaningful result from low concentrated samples at

Hi Jens, Here is my stab at pitching in. The x-ray fluorescence signal is a sum of the signals from all the N atoms in the sample that are in the x-ray beam. (Assume that the sample is not too thick so that all the fluorescent x-rays can get out of the sample.) The background slope of the spectra and the absolute signal values (detector gain, detector absorption, ect) are removed by normalizing the XANES signal. What this does is put your absorption signal on a relative scale rather than an absolute scale. Since the fluorescence signal is linear combination of the signals from each type of atomic environment of your sample, we can normalize the spectra and still get out the percentage of each phase based on its relative contribution. We can then compare spectra from different beamlines, and different detectors and come up with a relative percentage of each phase in the sample(s). We can not get the absolute concentration of that phase in the sample. HTH Shelly think the

N k-edge. I think my problem is than I don`t understand the physical meaning of a edge step normalized spectra. Is it the spectrum 1 x-ray photon would produce? Is it right that I loose the information of the absolute concentration after normalization so that I still can identify relative proportions of different compounds with in a sample but I can`t compare different spectra in an absolute way anymore? The extreme case would be a comparison of pure and a diluted spectra.

jens

ifeffit-request@millenia.cars.aps.anl.gov schrieb:

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Today's Topics:

1. Normalization of XANES spectra (Jens Kruse) 2. Re: Normalization of XANES spectra (Frenkel, Anatoly) 3. Re: Normalization of XANES spectra (Scott Calvin)

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Message: 1 Date: Wed, 29 Oct 2008 15:02:54 +0100 From: Jens Kruse Subject: [Ifeffit] Normalization of XANES spectra To: ifeffit@millenia.cars.aps.anl.gov Message-ID: <49086D0E.2000603@uni-rostock.de> Content-Type: text/plain; charset="ISO-8859-15"; format=flowed

Hi everyone,

I have a general question: I know Normalizing is something we do so that we can compare samples measured under different experimental conditions (removes the effect of

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gains ...) but I have problems in understanding and applying normalization when also quantitative conclusions are needed when comparing different spectra.

If I have two XANES spectra (a) and (b) measure under the same conditions but with different concentration of the absorbing atom with in different molecules.If both normalized spectra show a peak 1 , but this peak is higher in intensity in spectrum (a) than in spectrum (b), does this mean that compound which produced peak 1 is also absolute higher in concentration in sample/spectrum (a) or do I loose this information after normalization? Or can I just say: in the normalized spectrum (a) peak 1 is higher

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peak 2 suggesting that the compound leading to peak 1 is more abundant (just relative proportions).But I can't say: The intensity of peak 1 in the also normalized spectrum 2 is lower than in spectrum one, Therefore, the compound leading to peak 1 is less abundant in spectrum/sample

different than 2. ????

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I hope somebody can help me to understand this issue.

Thanks a lot,

jens

-- Jens Kruse Institute for Land Use Faculty for Agricultural and Environmental Sciences Rostock University Justus-von-Liebig-Weg 6 18059 Rostock GERMANY Phone: +49(0)381-498 3190

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