Hi guys, I have done SEM-EDX analysis of microalgae biomass. I have done the elemental analysis. However, the result also mentioned the value of apparent conc.,intensity correction, standard level and factory standard. But i could not figure out how to discuss it. I look forward to hearing your suggestion regarding EDX.
Thank you.
Nazia
As I understand, you got results of "quantitative" analysis. I bet they are wrong results. EDS quantification is very bad for organic specimens. If you are looking for some heavier elements in your specimens, then with help of EDS you can check whether you can detect them and range your specimens in order of amount of said elements.
You need qualified operator and good standards to try quantification of such elements as O and C, and even then it will be inferior to other analytical methods. Use them instead.
Thank you Valadimir. Here I am attaching the EDX result, may you please check and confirm me what is the wrong with the result please?
It's much better than I thought - actual standards were used. But it looks like analysis was performed by geologist, because oxide-oriented software package was used and carbon was ignored. But carbon is the main component of your sample, without it quantification makes no sense. And again, EDS is a poor, unreliable method in quantitative analysis of bulk biological specimens.
As for interpretation of your results, you should only pay attention to wt%, but not for results you have now (because carbon is missing). Do not use atomic% because hydrogen is not detected by EDS at all, and it can be a substantial part of atomic% composition (but it has low weight).
In your current results the most interesting parameter is "apparent concentration" Do not know this specific software, but it looks like not normalized wt%. It is the most real numbers you have for now. So, according to it your specimen has 7.9% of O, 0.09% of Mg and so on. And the rest is C. A lot of C... Carbon coating? Then standards should have the same coating. Did they? You have to talk to operator.
Hi Nazia,
In general, EDS is just a method of COARSE ESTIMATION. There are at least three fundamental limitations:
1. Depth. Only few micrometer-thick layer is examined. Obviously, there are a lot of artifacts - oxides (for inorganic samples), contamination, heterogeneity (for biological samples), etc.
2. Spatial resolution. The "X-rays source" on the surface is more than the beam spot. Typically, it is few cubic micrometers (well known bulb looking pictures from student books).
3. Concentration. The method is not so sensitive in comparison with quantitative analytical methods.
These limitation must be kept in mind. Especially, when you work with biological samples.
Good luck!
Thank you very much for your very useful replies. Vladimir, u r ryt about the C thing. I have repeated the sample run again today without carbon-coating of the sample what gave the real result of C (30.30 wt%) and O(40.87 we%) now. The machine maintained the vaccum process and for that case, H could not be measured. May you please let me know how to discuss the apparent conc.Currently the standard is without coating since i have done the work without coating.
Is concentration can be illustrated as limitations/error? @denis..may you please elaborate little more?
Thanks
nazia
You may want to check how close the sum of apparent concentrations is to 100%. If it is too far from 100% then something wrong with analysis. Otherwise use wt%.
Reminder: EDS is not good for full quantification of biological specimens.
It is very difficult to estimate the systematic error of the method. This task is more difficult than conventional statistical error calculations. Especially, for biological objects. Just for a tough illustration, I have painted this picture.
Just use more suitable methods for analysis of chemical composition: chromatography, mass spectroscopy, methods of classical analytical chemistry, etc.
Good luck!
Thank you very much Korneev. Your explanation is very helpful. I really appreciate your effort and explanation :)