Gas BenchII-IRMS测定地下水中溴同位素新技术

The novel method of bromine stable isotope measurement by Gas Bench II -IRMS was developed. Based on the chemical properties that bromine is easier to be oxidized than chloride by K2Cr2O7 , Br¯ is oxidized to Br2 while chloride still leaves in the solution, so bromine could be separated from chloride; bromide is precipitated in the form of AgBr by AgNO3, and then AgBr was converted into CH3Br for bromine stable isotope mass spectrometry analysis. In the chemical reaction, 20 μL CH3I and 0.5 mg AgBr were used. For the whole experiment, 4-10 mg bromine was used, the time of mass spectrometry analysis decreased from 1.5 h to 800 s, and the precision is better than ±0. 1‰（2σ）. The method could be used to determine bromine isotope in groundwater, and have a wide application in hydrogeology.