In situ oxygen isotope analysis with an excimer laser using F-2 and BrF5 reagents and O-2 gas as analyte

In situ oxygen isotope analysis of silicate minerals has been validated by interlaboratory calibration using an excimer laser (KrF fill gas, 248 nm), F-2 gas fluorinating reagent, and O-2 gas as mass spectrometer analyte. A value of delta(18)O(SMOW) = 5.82 parts per thousand (+/-0.03, 4 analyses) was obtained for almandine UWG-2 compared to a recommended value of 5.8 parts per thousand (Valley et al., 1995). The interhalogen BrF5 was tested by comparing in situ analyses made alternatively with either BrFS or Fa gas on crystals of almandine, epidote, forsterite, tourmaline, and zircon. Results for different pressures of BrF5 (20 to 40 ton) in the reaction chamber show that delta(18)O values decrease by 1 permil for an increase of 10 ton in BrF5 pressure. In strong contrast, delta(18)O values measured with purified F-2 gas are precise and accurate over a range of from 15 to 150 ton F-2 gas pressure. Use of F-2 gives higher yields of O-2 than with BrF5. Values of delta(17)O and delta(18)O measured in situ on a variety of silicates all plot on the terrestrial mass fractionation line, provided that NF3 contamination is eliminated from the O-2 gas analyte. Copyright (C) 1997 Elsevier Science Ltd.