Determination of Boron Isotope in ZrB₂ by Positive Thermal Ionization Mass Spectrometry with Direct Fusion

Positive thermal ionization mass spectrometry (PTIMS) method was used to determine boron isotope in ZrB₂ for Na₂BO₂⁺ with m/z 88(²³Na₂¹⁰BO₂⁺) and m/z 89 (²³Na₂¹¹BO₂⁺) as analytical ion. Imported high purity tantalum belt was used as sample filament. The isotope interference, coating technology, pretreatment of the ZrB2 sample were researched. There is no interference of strontium and yttrium in the background by mass peak scanning and analysis, while the effect of oxygen isotope was deducted by formula. The graphite was attached to the sample filament with diluent graphite slurry instead of graphite turbid liquid as emission reagent. The method of which used Cs₂BO₂⁺ as analytical ion was reproduced by samples coating with graphite slurry, and using diluent graphite slurry instead of graphite turbid liquid. Enhanced effect of graphite on Na₂BO₂⁺ emission was proved by comparison with the direct coating method. Although the effect was inapparent about the enhanced effect of graphite on Cs₂BO₂⁺ emission, the reduction of ion beam was inhibited effectively in analysis after adding graphite. The phenomenon shows that graphite coating method is propitious to gain stabler ion beam and improve the precision of analytical results. The value of boron isotope standard substance was reproduced, and the analytical value was consistent with the standard value. When sample quantity was 8.0 μg, acid dissolution sample application and direct fusion sample application were compared. The results show that the direct fusion sample application is not easy to introduce interference ions, and the precision is less than 0.020%. This method can shorten the time of sample pretreatment and improve the detection efficiency.