Why Nitrogen can not be detected by EDX?

Dear Rupa Chakraborty ,

you may share the elemental composition of your adsorbent.

There may be a peak overlap of N K-alpha (392eV) with one of the adsorbent elements such as e.g. Ti or Sn for example.

What is the detector material and excitation energy?

You also may share the EDX spectrum which should show the N.

Thanks in advance

Just take into account that the EDS detection efficiency for low-Z atoms is low, and if other heavier atoms contributions overlap (even partially) it will be very hard or impossible to quantify any Nitrpogen peak (as Dr Martens wrote).

Moreover, if your SEM/EDX equipment is a "standard" one, a significant fraction of the Kalpha X-rays coming from Nitrogen in your sample will be absorbed by the berillium window that separates the sample chamber from the analyser.

In few words, EDX is not a proper technique to detect Nitrogen, unless :

- you have a large fraction of N in your sample

- you do not have peaks from heavier components falling too close to an expected N peak (around 392 eV)

- your equipment is designed to minimise undesired X-ray absorption (e.g., very thin berillium window).

By the way, you says the measurements were done on an adsorbant containing organic radicals, if I have well understood. If that material is not an elctric conductor, it will possibly be locally over-heated by the primary electrons, that in turns may easily cause dissociation and loss of volatile by-products (that could involve Nitrogen!), or even local fusion.

Dear Giuseppe Curro,

Thank you for sharing your opinion and I have used chicken feather as an adsorbent material it is a biological material not any conducting material.

Dear Rupa Chakraborty ,

thanks for the info.

I think your chicken feather will mainly contribute to the C and O peaks.

The position of the N peak ( N- K-alpha) will lie between the C and the O K-alpha. If the total concentration of N is much lower than that of C and O you will not see the peak because of the limited resolution of 136eV of the detector system.

C K-alpha = 277eV, N K-alph a= 392eV and O K-alpha = 525eV.

Dear Rupa Chakraborty,

You could not find your N because of its low-Z number and its overlapping with the C and O K-alpha. You could try manually to add N to your spectrum. The microscope will find a certain amount of N though low.

Good luck!

Maria

Dear Gerhard Martens

May be you are right. Thank you for the suggestions.

Dear Maria Plamenova Nikolova,

Thank you for the information.

Dear Maria Plamenova Nikolova,

Do you have any research paper related to this reason? If you have please send me. Thank you for advance.

Rupa

From your FTIR analysis you may estimate the expected concentration of N ( e.g the upper limit of N) and compare the data with the EDX findings of C and O and draw your conclusions with respect to the things said above.

Dear Gerhard Martens

Thank you for the suggestions

Dear Gerhard Martens

FTIR analysis is not quantitative but qualitative analysis. Therefore how can she estimates the nitrogen amount?

FTIR analysis is not quantitative but qualitative analysis.

Dear all, you are right that FTIR is a not a quantitative analysis technique. But it is not the first time that feathers were analyzed. So it should be possible to gather any informations on estimations of elemental compositions the feathers, at least on how much N should roughly be present compared to C or O.

If the expected N concentration is in the same order as C and O, the N peak should clearly show up in the EDX spectrum, even when there is limited energy resolution of about 130eV. If N/C and N/O is small than the superposition by the feet the neighbouring C and O peaks will burry the N peak.

Fortunately I found the following link on composition of hair, which mainly contains keratine, such as the feathers.

https://www.cesareragazzi.com/en/structure-and-chemical-composition-of-hair

It is stated there:

" The main chemical elements present in hair are composed of carbon (45%), oxygen (28%), nitrogen (15%), hydrogen (6.7%) and sulphur (5.3%) ."

So from this info one should expect an N peak at at roughly 1/3 of the C peak and about 1/2 of the O peak.

Be careful in saying FTIR is not a quantitative analysis. Arthur Braun is right.

The following links are just few examples in a plethora of reported cases:

... and many more

Dear Reza Fotohi

Thank you so much. It is really helpful for me.

Nice reference Reza Fotohi ,

in a former information (is somehow deleted) Rupa Chakraborty showed her spectrum and mentioned the energy resolution of about 130eV.

Your spectrum is showing a resolution of about 50eV. So the N peak is not really affected here by the C and O peak.

Dear Gerhard Martens

Thank you so much for the information of hair keratin. Please explain to me C and O not affected to N peak so what is the reason of N is disappeared?

Dear Rupa Chakraborty ,

there is above a nice hint of Giuseppe Curro , who mentioned that the N could 'disappear' due to locally overheating the sample by the electron beam.

In fact I have googled for 'pryolysis of feathers' and found a hint for turkey feathers pyrolized at high temperatures *). They claimed that HCN would show up. Boiling point of HCN is at 26°C; so the HCN will go off in the vacuum system of your SEM and will remove the N from your sample.

You should check your sample with an optical microscope whether there is a damage of your sample from the SEM.

*) I will try to find this paper again.

Here it is:

Dear Rupa Chakraborty , next idea:

I do not know whether your SEM is going to do that.

In oder to avoid a material removement during EDX acquistion you should perform the spectrum acquisition not at a fixed point of the sample, but during a quick scan across the sample. The overheating will not be completely prevented, but there will be almost no time for any arising gas to remove from the electron spot at the instants of EDX acquisition.

If a scan of the electron beam is not possible during EDX acquisition, you may alternatively scan the sample by the sample stage relative to the electron beam (but this will be a quite 'low speed' alternative).

Good luck

Dear Gerhard Martens

Thank you so much for the information of "pyrolysis of feather" and good suggestions for future research work

Dear Rupa,

what Gerhard sir said is right FTIR is not quantitative analysis for estimation of the element. you can confirm the amount of N in your material by AAS or ICP-OES analysis.

what is your sample thickness for EDX? If N is in a deeper region it might not see by EDX analysis. the penetrating energy in EDX analysis also important for how much deeper it can penetrate.

Dear Sadanand Pandey,

Thank you for the information

Dear S Kalaiselvan,

Thank you for the information.

Nitrogen x-ray line is absorbed be Be ( window material) and some contaminant which could be around making its detection very difficult. However, there are techniques to ensure the nitrogen detection. Please look for references in the literature.

The cause its associated to your low atomic weight.

Dear Rupa

Try to use WDS (wavelength dispersive spectroscopy)rather than EDS(energy dispersive spectroscopy)because of the low atomic number of the N. It is well known that WDS is a slower technique than EDS, but WDS is more accurate than EDS for detecting elements with low atomic numbers,i.e., O & lower than O.

The reason is very simple. EDX is related to the K-shells which are not the valence shell. Nitrogen does not have a K shell, or , better to say, it has only a K shell in covalent bonding and this only electron is shared. In energy dispersion SEM you can be reliable signal from about Na on, in wavelength dispersion SEM you can see the second row elements too.

Thank you so much all of you for your valuable suggestions, information & opinions.

Hi,

Nitrogen produces a very weak response and also limited by the detector design, a unreliable detection is observed for N2 for most materials. X-ray absorption is a function of the energy of X-rays. Low energy peaks will be more strongly absorbed than high energies ones. Instead prefer to use WDS it will give better results in this case. For more details refer to http://crf.coe.drexel.edu/LinkClick.aspx?fileticket=mHznLUuMkv0=

Dear friends, pleas stop this idiocy about non-detecting light elements. C and O were detected. Try to comment on things you do know.

Hello Prof Dusevich, please avoid negative comments. Young researchers are using this platform to discuss their doubts. If you feel some answer/ information is wrong please correct it. Regards.

Even B can be detected with conventional EDX. The problems start at quantitative level... But quantitative EDX is a tricky and not very reliable technique itself.

Just a comment to the 'new' readers of the question and the answers here.

In a quite early stage of the answers Rupa Chakraborty has shared the spectrum but unfortunately she has withdrawn it. It indeed exhibits a strong C as well as a strong O signal as Vladimir Dusevich mentioned above. So the lack of N is not due to the disability of the detection of low elements in that energy regime here. Energy resolution, as I have seen, is/was quite good, so that N with a concentration larger than about 15 to 20% of C or O should be clearly visible in the spectrum.

... and eventually we came to a conclusion, that may sound (at least in my opinion) really promising.

In the Rupa's sample the at. concentration of N is well below C and O values in a subsurface volume comparable with the EDS depth resolution, This may happen in two alternative cases.

case1 : it is so since the very beginning, that is the native unperturbed sample composition is already lacking of significant amounts of N in te subsurface,

OR

case2 : N content in the EDS-probed region is strongly affected by the same SEM analysis (volatile by-products?)

An FTIR analysis on the virgin sample might help in deciding between the two cases above, just reminding that FTIR is not appropriate for a reliable "absolute" quantitative analysis, but may perform very well as a "relative" quantitatitive analysis, as Gerhard Martens and Artur Braun (and myself) have suggested several answers above.

I hope Rupa Chakraborty had the opportunity to take a step forward in her experiments and analyses in the last month

Thank you very much for your valuable suggestions.