Generation of O2 from BaSO4 using a CO2-laser fluorination system for simultaneous analysis of δ18O and δ17O

With the observation of mass-independent isotopic anomalies in numerous atmospheric molecules, the ability to measure both delta(17)O and delta(18)O in a range of samples is needed. Sulfate oxygen isotopic studies conventionally report only delta(18)O values. Recent findings indicate that sulfate delta(17)O and delta(18)O values, particularly the Delta(17)O value (= delta(17)O - (0.52)(delta(18)O)), provide independent information on the origin, mixing, and transformation of sulfate in the atmospheric and surface environments, which is not resolvable by only delta(18)O measurements. Existing methods for analyzing sulfate delta(17)O and delta(18)O are extremely laborious and demand high-purity BrF5. Here we report a novel method of generating O-2 directly from Barite (BaSO4) for simultaneous analysis of delta(18)O and delta(17)O by isotope ratio mass spectrometry (IRMS). The method utilizes a CO2-laser fluorination system that can also be used to quantitatively generate O-2 from silicates and oxides. Partial but consistent oxygen yields from BaSO4 are obtained for samples >4 mg. Correction factors of +9.4 parts per thousand for delta(18)O and 4.89 parts per thousand for delta(17)O are obtained, and there is no deviation in the Delta(17)O value due to the nonquantitative O-2 generation. The system may process more than a dozen samples per working day, with analytical error of +/-0.05 parts per thousand and +/-0.8 parts per thousand for Delta(17)O and delta(18)O, respectively. This new method is ideal for studies emphasizing an accurate sulfate Delta(17)O value.