Gas Bench Ⅱ-IRMS测定地下水中溴同位素新技术

摘要

建立了利用Gas BenchⅡ联用同位素比值质谱仪(Gas BenchⅡ-IRMS)用于测定地下水中溴稳定同位素的方法.基于溴比氯更容易被重铬酸钾氧化的性质,将Br-氧化成Br2,而氯残留在原溶液中,从而把溴与氯分离开；再利用AgNO3将溴以AgBr的形式沉淀下来,然后将AgBr转化成CH3Br进行溴稳定同位素质谱测定.反应中,CH3I用量为20 μL,AgBr用量为0.5 mg.本测试流程需溴4～10 mg,质谱测试时间由1.5h缩短为800 s,测试精度优于±0.1‰(2σ).该方法可以用于地下水中溴同位素测定,在水文地质研究中具有广阔的应用前景.%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. 20μL 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. L‰(2a). The method could be used to determine bromine isotope in groundwater, and have a wide application in hydrogeology.