Dear Jessica,

I am not familiar with your XRF system.

So I can give only general hints:

Na K-alpha is at about 1 keV; that's a quite low photon energy. So x-ray attenuation of the sample (especially in the presence of medium to high Z material) is quite large with respect to Na K-fluorescence .

Your Na may be too far away from net sample surface and even too low in concentration.

You should check your system via a sample, which definitely is containing Na up to the surface (e.g. NaCl from your kitchen).

For excitation of Na the 15kV setting is quite enough.

Vacuum is necessary for preventing Na K-alpha attenuation by air. Setting of 'No filtration' is ok for exciting radiation and is a must for Na K-fluorescene.

Your detector window (if a window is present at all at that low photon energy) might be 'dirty' giving rise to significant Na K-fluorescence attenuation.

You mention that you have 'optimized the settings for other metals'; does it mean that you have got metals in your sample? What further metals are being present in your sample(s)?

The fluoresence lines ( L-lines) of some of these metals my burry your Na K-fluoresecne your are searching for.

According to the x-ray line table*) in the attachment you will see that L-lines of atoms having atomic numbers around Z= 30 (Zn) are very close to Na K-alpha. I do not know the energy resolution of your detector. So in addition to Zn even L-lines of Ni (Z=28), Cu (Z=29), Ga (Z=31) and Ge (Z=32) may interfere with your Na K-alpha.

*) taken from the J. A. Bearden table in CRS Handbook of Chemisty and Physics.

The range of 1 keV in water is only 1 micrometer. At this point, self-absorption in the samples is very dominant and I would think that it is maybe worth the effort to think on (reproducible) sample preparations/geometries than just machine settings.

Gerhard Martens had a great explanation. Further Gerhard Martens information, I would like to say that this p-ED-XRF device has very low efficiency to detect low Z elements (

Elton,

thanks for sharing more details about the XRF system.

Two windows are over-kill for Na K radiation.

If you have access to an ion beam accelerator, you may use particle induced X-ray emission (PIXE) and particle induced gamma ray emission (PIGE) techniques. They both can provide valuable information regarding sodium determination in your samples.

Thank you everyone. Gerard, thank you for such a thorough response. To answer your question, I have separate samples with copper, zinc, cadmium, strontium and lead which I am also analyzing separately. I am using different conditions for each metal as recommended by Bruker and an MIT document, which worked beautifully, but I couldn't find any recommendations for Na.

Elton, thank you also. That was my suspicion but I wanted to ask others for recommendations just in case.