Hydroxyapatite via EPMA

[BenjaminWade]

Hi all
I have a student who wants to measure Ca concentrations in shark vertebrae, and it is predominantly composed of HAP. I have come up with a basic list of major and minor elements having done wavescans on the vertebrae, and picked some background locations. I was wondering if anyone has had any tips or experience with analysing HAP via EPMA with regards to what standards were used, beam conditions, expected totals (and how to enter the O-H stoichiometry into the Probe for EPMA software...)

Cheers

[qEd]

Ben,
Here is a paper published a few years back regarding an approach to quantitative analysis of a beam sensitive mineral.
Ed Vicenzi

Edit by John: Ed is too modest. It was his idea to implement a method for calculating excess oxygen as H2O/OH in PFE.

The idea is simply to measure all your cation elements plus oxygen (which is a whole other topic that we can go into another time), and then calculate your stoichiometric oxygen using the Display Results As Oxides checkbox seen here (assuming your cation valences are sufficiently known).



The program will take your measured oxygen and subtract from it the calculated oxygen, based on the specified cation formulas in the Elements/Cations dialog, to obtain the actual excess (or deficit!) oxygen.

Then using the Hydrogen Stoichiometry To Excess Oxygen feature, specify the H to O ratio and let 'er rip!

[BenjaminWade]

Awesome, thanks for the tips. I will give it a go.
Sorry for the late reply. Had my wisdom teeth out last week. Great fun..

[John Donovan]

Ugh, not too much fun if I remember my experience!

You might want to check this thread on the TDI correction in Probe for EPMA for beam sensitive samples:

http://probesoftware.com/smf/index.php?topic=62.0

[jon_wade]

Awesome, thanks for the tips. I will give it a go.
Sorry for the late reply. Had my wisdom teeth out last week. Great fun..

Now thats dedication to the cause, but I'm sure theres a less painful way to get hold of a standard or two!

(Ben - we're not related are we? )

[BenjaminWade]

Thanks John. Yep I have/had the TDI on. Just on the TDI is there any reason to ever NOT enable it? I just leave it on even if the elements I am analysing are historically seen as "stable" under the beam. I know that enabling the TDI probably adds to the acquisition time slightly, but not too much.

Edit by John: it doesn't hurt anything to leave the TDI acquisition enabled as you say, just a slight overhead.

Jon, I didn't even think of that! But I was planning on doing some 3D reconstructions of them and lasering them. Perhaps I will probe them too....

[Probeman]

Another paper related to water in EPMA by Diana Roman showing how important it to include water by difference in the matrix correction (see attached below). See graph comparing water by difference to water by FTIR.

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