Hydrogen and D/H analysis of apatite by Elemental Analyzer-Chromium/High-Temperature Conversion-Isotope Ratio Mass Spectrometry (EA-Cr/HTC-IRMS)

Abstract

Hydrogen and δD measurements of the mineral apatite have been used to measure volatile contents of planets and planetesimals and to infer the sources and evolution of water throughout the solar system. All of these studies use Secondary Ion Mass Spectrometry (SIMS) which necessitates the use of apatite mineral standards to correct for matrix effects, which have previously been measured by mass spectrometry for hydrogen isotopes. Here we present a new technique of Elemental Analyzer-Chromium/High Temperature Conversion-Isotope Ratio Mass Spectrometry (EA-Cr/HTC-IRMS) for the measurement of hydrogen and hydrogen isotopes of apatite. This technique presents greater technical advantages over TC/EA due to ability of chromium to bind with phosphorus in the high-temperature reactor, and prevent this elemental P from clogging the instrument components. We also show that removal of adsorbed moisture of nominally hydrous minerals and glasses becomes increasingly important with decreasing grain size of materials and present experiments on moisture removal from nominally anhydrous quartz. We report hydrogen and hydrogen isotope results of five fluorapatite and two hydroxylapatite samples, including Durango apatite. We show that our results of hydrogen content of Durango apatite are similar to published values using the TC/EA technique. Our recommended values for hydrogen using a Cr reactor for H2O and δDVSMOW-SLAP for Durango apatite are 608 ± 102 ppm H2O and δDVSMOW-SLAP = −86 ± 4‰ (2σ).