Development of a technique for mass spectrometric measurement of δ18O of aqueous sulphate

Application of stable isotopes of hydrogen and oxygen as tracers in hydrology for studying the origin of water is well established. δ18O of water molecule itself is used for identifying the source of water whereas δ18O of dissolved oxy anions (such as carbonate, phosphate, sulphate, nitrate and silicate) present in the same water reveal their source of origin. δ18O of SO4 finds applications in identifying the origin of sulfate i.e. marine, marine evaporite or non-marine in nature and as a geothermometer in determining subsurface temperature of geothermal waters. A vacuum line of glass was fabricated to measure δ18O of aqueous sulfate. This paper deals with the technique and results of a trial with NBS-127, Sea water barium sulfate