With the concentrations you are dealing with this might be an issue. Indirect methods are more plentiful such as the below articles:

Article Examination of hydrogen embrittlement in FeAl by means of in...

Article Examination of hydrogen embrittlement in FeAl by means of in...

Or if you come up with a novel way then you would be able to publish the method. I assume the atomic concentration is a challenge to detect. You could always try XPS or some surface technique but hydrogen atoms are in general considered poor at scattering x−rays so that might not work in the end. If resources allow you might possibly try performing x−ray diffraction at low temperatures in which the thermal motion of the atoms are significantly reduced and might detect hydrogen. Or try neutron diffraction as hydrogen scatters neutrons more effectively and hence the M−H bond distances can be measured more accurately. A limitation of neutron diffraction method is that large sized crystals are required for this kind of study. Good luck.