A comparison using Faraday cups with 10(13) amplifiers and a secondary electron multiplier to measure Os isotopes by negative thermal ionization mass spectrometry
A comparison using Faraday cups with 10(13) amplifiers and a secondary electron multiplier to measure Os isotopes by negative thermal ionization mass spectrometry
复制标题
使用带有 10(13) 放大器和二次电子倍增器的法拉第杯通过负热电离质谱法测量锇同位素的比较
DOI：
10.1002/rcm.7943
复制
发表时间：
2017
影响因子：
2
通讯作者：
Xu Jifeng
中科院分区：
文献类型：
--
作者：
Wang Guiqin;Sun Tiantian;Xu Jifeng
根据约翰逊-奈奎斯特噪声方程，电子噪声值与电阻值的平方根成正比。这种关系给出了理论上的改进， 方法在负热电离质谱（NTIMS）中，采用1013 Ω放大器的静态法拉第杯，测量Os同位素，并与1011Ω放大器和单二次电子倍增管（SEM）跳峰法测量结果进行比较。我们在187 OsO 3的强度范围内分析了大负载的Os（1 μg）（0.02-10 mV），外加少量Os负载结果使用1013Ω放大器，在187 OsO 3强度为0.02 mV和10 mV时，Merck Os测定的长期重现性为187 Os/188 Os = 0.1211 ± 0.0086和0.120229 ± 0.000034。同时，分析的5和500 pg的JMC Os载量显示187 Os/188 Os = 0.10669 ± 0.00036和0.106807 ± 0.000023。相比之下，通过SEM测量的值为187 Os/188 Os = 0.10704 ± 0.00056和0.10690 ± 0.00013。结论1013Ω放大器和扫描电镜在10-50 pg范围内测定Os的准确度和精密度相同，但前者的分析时间可缩短约2/3。对于<10 pg的Os量，SEM测量仍然是最精确的方法，但使用1013Ω放大器的分析表明，对于>50 pg的Os量，它们明显优于SEM。
RationaleAccording to the Johnson‐Nyquist noise equation, the value of electron noise is proportional to the square root of the resistor value. This relationship gives a theoretical improvement of in the signal/noise ratio by going from 1011Ω to 1013Ω amplifiers for Faraday detection in thermal ionization mass spectrometry (TIMS).MethodsWe measured Os isotopes using static Faraday cups with 1013Ω amplifiers in negative thermal ionization mass spectrometry (NTIMS) and compared the results with those obtained with 1011Ω amplifiers and by peak‐hopping on a single secondary electron multiplier (SEM). We analysed large loads of Os (1 μg) at a range of intensities of187OsO3(0.02–10 mV) in addition to small loads of Os (5–500 pg) to compare the results of the three methods.ResultsUsing 1013Ω amplifiers, the long‐term reproducibility determined from Merck Os was187Os/188Os = 0.1211 ± 0.0086 and 0.120229 ± 0.000034 at 0.02 mV and 10 mV of187OsO3intensities. Meanwhile, the analysed JMC Os loadings of 5 and 500 pg showed187Os/188Os = 0.10669 ± 0.00036 and 0.106807 ± 0.000023. In comparison, the values measured by the SEM were187Os/188Os = 0.10704 ± 0.00056 and 0.10690 ± 0.00013. All errors are in 2 standard deviation (SD).ConclusionsBoth the accuracy and the precision determined using the 1013Ω amplifiers and the SEM are identical when the Os amounts are within 10–50 pg. However, the former analysis time can be shortened by approximately two‐thirds. The SEM measurement is still the most precise method for Os amounts <10 pg, but the analyses using 1013Ω amplifiers suggest they are significantly better than the SEM for Os amounts >50 pg.