High Precise Determination of Bromine Isotopic Ratios by Positive Thermal Ionization Mass Spectrometry Using Static Multicollection Based on Cs2Br+ Ions

A high precise determination of stable bromine (Br) isotopic ratios was achieved by thermal ionization mass spectrometer (TIMS) triton with 8 kV accelerating voltage using static multicollection of Cs2Br+ ions. The effect of B and Cl content on the measurement of Br isotope was studied. The static multicollection method had many advantages, such as high precision ( external accuracy lies between 0.09 parts per thousand-0.18 parts per thousand), small amount of sample loading ( 10-20 mu g Br) and short acquisition time (just 8 min for 100 cycles). The results showed that the effect of co-existing Cl on the measurement of Br isotope ratio increased with the increase of Cl content, and that the presence of B made the determined bromine isotope ratio lower than that without B. The effect of the sample loading sequence on the results of the determined Br isotopic ratio was insignificant. Meanwhile, the four bromide of Br isotopic composition were determined, its delta Br-81 was between 0.61 parts per thousand-1.68 parts per thousand, showing a significant Br isotope fractionation.