  Analysis and understanding of the role of hydrogen in metals is a significant
challenge for the future of materials science, and this is a clear objective of
recent work in the atom probe tomography (APT) community. Isotopic marking by
deuteration has often been proposed as the preferred route to enable
quantification of hydrogen by APT. Zircaloy-4 was charged electrochemically
with hydrogen and deuterium under the same conditions to form large hydrides
and deuterides. Our results from a Zr hydride and a Zr deuteride highlight
challenges associated to accurate quantification of hydrogen and deuterium, in
particular associated to the overlap of peaks at low mass-to-charge ratio and
of hydrogen/deuterium containing molecular ions. We discuss possible ways to
ensure that appropriate information is extracted from APT analysis of hydrogen
in a zirconium alloy systems that is important for nuclear power.
