Relative Sensitivity Factors of 2H and 16O2H relative to 18O in deuterium-implanted spinel-structured oxides

To allow the analysis of hydrogen in spinel-structured oxides (hereafter referred to as “spinels”) by secondary ion mass spectrometry, Relative Sensitivity Factors (RSFs), which are typically matrix-dependent, need to be determined. Matrices in natural spinels vary significantly due to the wide range of solid solutions that these nominally anhydrous minerals display. Previous work (Zellmer et al., 2025) has presented RSF values of 16O2H relative to 18O for five natural spinels of variable Al2O3 content. Using the same implanted crystals, we have here expanded this dataset with additional spinels, applying depth profiling under different conditions in a different laboratory. We provide the RSF values of 16O2H relative to 18O, which match the previously available data. We also provide the RSF values of 2H relative to 18O. This in principle allows analysis not only of the OH dimer, but also the H monomer for hydrogen analysis in spinels. However, we note that the significantly higher RSF values for 2H, here between 1.12 x 10^22 and 3.01 x 10^22 atoms per cm3, suggest dimer analysis is preferable because hydrogen monomer count rates will be low. For the RSF of 16O2H relative to 18O, our data confirm an increase with increasing Al2O3 content, here from 2.59 x 10^20 to 2.51 x 10^21 atoms per cm3. When we combine our new data and those of Zellmer et al. (2025), the increase of this RSF with Al2O3 follows a second order polynomial form: RSF = 1.52 x 10^17 Al2O3^2 + 2.12 x 10^19 Al2O3 + 2.76 x 10^20, yielding an r2 value of 0.974, where r is the correlation coefficient. The relative uncertainties in the RSF values based on repeat analyses are circa ±35% (2SE) for 2H relative to 18O and circa ±23% (2SE) for 16O2H relative to 18O, again suggesting that hydrogen analysis should target the OH dimer rather than the H monomer. One ilmenite sample gave RSF values of 3.40 x 10^22 atoms per cm3 (±39.2%, 1RSD) for 2H, and 8.11 x 10^20 atoms per cm3 (±0.5%, 1RSD) for 16O2H. This sample will, however, not be considered further here.