Determination Of Halogens In Geological Reference Materials Using Neutron Irradiation Noble Gas Mass Spectrometry

We determined the heavy halogen (Cl, Br, and I) concentrations of fourteen powdered geological reference materials distributed by the Geological Survey of Japan (GSJ) and the US Geological Survey, and seven original blocks of GSJ geological reference materials, using neutron irradiation noble gas mass spectrometry (NI-NGMS). The halogen concentrations obtained from the powder and original blocks of geological reference materials are systematically lower than their reference values for low-concentration samples. This discrepancy can be explained by contamination on the sample surface during the preparation of the reference materials. Contaminated halogen-derived noble gases were, at least partially, removed before analysis during preheating of the samples under vacuum after sample loading. The presence of the contaminated component in the reference materials is not a matter for other analytical methods as long as the contaminated component is completely homogenized in the powder reference materials and not removed before analysis. However, the present results indicate that the standard materials used in NI-NGMS should be selected more carefully than those used in other methods. In addition, we propose an F-determination method using NI-NGMS based on Ne systematics of neutron-irradiated samples.