SIMS simultaneous measurement of oxygen–hydrogen isotopes and water content for hydrous geological samples

In this study, we developed two new SIMS (secondary ion mass spectrometry) analytical protocols to simultaneously measure oxygen–hydrogen (O–H) isotopic compositions and water content for hydrous geological samples. These two protocols involve the measurement of two sets of secondary ion contents: (1) 1H, 2H, 16O, 18O; and (2) 16O, 16O1H, 18O, 17O1H, 16O2H. Both measurements utilize a hybrid dynamic multi-collector system of CAMECA IMS 1280-HR, which benefits from both the static multi-collector mode and peak-hopping mono-collector mode. These new methods can simultaneously measure (with high-precision) the 18O/16O ratio in static multi-collector mode without trading off its analytical precision, and 1H/16O (or 16O1H/16O) and 2H/1H (or 16O2H/16O1H) ratios in conventional peak-hopping mono-collector mode. Three glass samples (LBS7H, LBS5H and LBS6H-) with known water contents and two apatite samples (Kovdor, Durango) with known oxygen–hydrogen isotopes and water content were measured to verify the protocols' reliability. The olivine crystal San Carlos with ∼1 ppmw water content was used for background monitoring. For the apatite samples, the external precision (spot-to-spot reproducibility) for δ18O and δD is better than 0.56‰ (2SD) and 54‰ (2SD), respectively. After eliminating the outlier (beyond 3SD error), the external precision of 16O1H/16O or 1H/16O ratio improves to 10.27% (2SD). For the glass samples, the water content calibration curves, which were constructed by comparison of the known water content with the SIMS measured 16O1H/16O or 1H/16O ratios, yielded good correlations. It is noteworthy that the apatite and glass samples can have a uniform water content calibration curve for protocol 1, but not for protocol 2, indicating different matrix effects for the two protocols.