激光共振电离质谱法测量锡的同位素比

采用实验室研制的激光共振电离质谱仪,建立了锡(Sn)同位素的激光共振电离质谱分析方法.测量了锡原子的自电离态光谱,确认了锡的一条三色三光子共振电离路径,其各步激发/电离的激光波长分别为λ1=286.4 nm、λ2=811.6 nm、λ3=823.7 nm;通过将样品与氧化石墨烯溶液混合制样,有效提高了锡样品的电热原子化效率,1μg锡的总探测效率达到3×10-5以上,是直接滴样方式的4.5倍左右.采用本方法对锡、锑、硫(1:1:1,m/m)混合模拟样品进行测试,实现了锡的选择性电离,有效避免了测量过程中锑、硫对锡的同量异位素干扰,样品中主要同位素比116 Sn/120 Sn,117 Sn/120 Sn,118 Sn/120 Sn和119 Sn/120 Sn测量的相对标准偏差均°1%.结果表明,本方法能够有效解决TIMS、ICP-MS等商业质谱仪在锡同位素质谱分析过程中的同量异位素干扰难题,有望应用于反应堆乏燃料中裂变产物121m Sn、126 Sn的测量.

Measurement of Tin Isotope Ratios by Laser Resonance Ionization Mass Spectrometry

A preliminary method based on the laser resonance ionization mass spectrometer ( LRIMS ) developed in the laboratory was established to determine tin isotope ratios. By measuring the auto-ionization spectrum of tin atoms, a three-color-three-photon resonance ionization scheme was confirmed, and the laser wavelengths of each excitation/ionization step were λ1=286. 4 nm,λ2=811. 6 nm and λ3=823. 7 nm. More effective electrothermal atomization of tin was implemented by mixing the samples and grapheme oxide solution, and the total detection efficiency of 1μg of tin sample was above 3×10-5, which was about 4. 5 times as high as the method of directly dropping samples. A tin-antimony-tellurium mixture at a ratio of 1:1:1 ( m/m) was prepared as a simulant sample, and the major tin isotope ratios in the sample were determined. Results showed that the isobaric interference from antimony and tellurium was effectively avoided, and the relative standard deviations for 116 Sn/ 120 Sn, 117 Sn/ 120 Sn, 118 Sn/ 120 Sn, 119 Sn/ 120 Sn were all better than 1%. This work indicated that LRIMS could effectively avoid the isobaric interference in the measurement of tin isotope ratios, and could be applied to measure the fission product 121m Sn and 126 Sn in the reactor spent fuel.