Reduction of OH contamination in quantification of water contents using NanoSIMS imaging

Quantification of water content is relevant in various topics in geology and planetary sciences. NanoSIMS has capabilities for high spatial resolution imaging and offers opportunities to accurately quantify water contents at fine scale on small surface areas. The main concern using ion microprobe techniques is to estimate and minimize contribution of water contamination, from residual gas in the sample chamber, sticking onto the surface of the sample. Here we tackle a set of sputtering/analytical parameters and we evaluate their relative influence on the OH−/Si− ratio. We demonstrate that a high erosion rate, reached using a primary beam intensity of ~ 25 pA, is sufficient to lower this OH contamination for basaltic glass. This leads us to describe a procedure to correct for OH contamination and thus determine accurate values of OH/Si ratio in order to quantify water contents in silicate materials using NanoSIMS imaging.