Background effects on Faraday collectors in gas-source mass spectrometry and implications for clumped isotope measurements
Background effects on Faraday collectors in gas-source mass spectrometry and implications for clumped isotope measurements
复制标题
DOI：
10.1002/rcm.6490
复制
发表时间：
2013-03-15
影响因子：
2
通讯作者：
Rutz, Tanja
中科院分区：
文献类型：
--
作者：
Bernasconi, Stefano M.;Hu, Bin;Rutz, Tanja
原理通过质谱法测量次要同位素体的丰度需要校正质谱仪中的细微非线性，这些非线性会导致实际同位素比与测量同位素比之间的关系出现偏差。在这里，我们表明，负背景的法拉第杯记录的次要离子束的CO2同位素的测量中观察到的非线性的原因，并提出了一个新的校正程序成团的同位素测量。方法对两种质谱仪测定CO2微量同位素13 C18 O 16 O（m/z 47）丰度时产生非线性效应的原因进行了研究。通过使用不同组成的气体与接近随机和非随机分布的同位素，我们证明了过量丰度的m/z 47的CO2的散装同位素组成的明显依赖性是由于背景干扰，这是线性依赖于在质谱仪的源中的气体的分压。结论：本底测定与气体流入源的质谱仪是必要的准确测量CO2的凝聚同位素。如果m/z 44法拉第杯的狭缝宽度显著超过m/z 47的狭缝宽度，则可以使用m/z 44信号强度与m/z 47背景中的相应最小值之间的相关性来精确地执行背景校正。我们提出了两个新的校正方案，减少了耗时的测量不同的散装同位素组成的气体。这些发现也可能与质谱法测量其他稀有同位素有关。版权所有（c）2013约翰威利父子有限公司
RATIONALE The measurement of the abundances of minor isotopologues by mass spectrometry requires correction of subtle non-linearities in the mass spectrometer that cause deviations in the relationship between actual and measured isotope ratios. Here we show that negative backgrounds on the Faraday cups recording the minor ion beams are the cause of the observed non-linearities in the measurement of CO2 isotopologues, and propose a new correction procedure for clumped isotope measurements. METHODS We carefully investigated the cause of non-linearity effects in the measurement of the abundance of 13C18O16O, a minor isotopologue of CO2 with m/z 47, on two different mass spectrometers. By using gases of different composition with close to stochastic and with non-random distribution of isotopes we demonstrate that the apparent dependence of the excess abundance of the isotopologue of m/z 47 on the bulk isotopic composition of CO2 is due to a background interference that is linearly dependent on the partial pressure of the gas in the source of the mass spectrometer. CONCLUSIONS Background determination with gas flowing into the source of the mass spectrometer is necessary for accurate clumped isotope measurements of CO2. Background corrections can be performed accurately if the slit width of the m/z 44 Faraday cup significantly exceeds that of the one for m/z 47, using a correlation between m/z 44 signal intensity and the corresponding minimum in m/z 47 background. We propose two new correction schemes that reduce the time-consuming measurement of gases of different bulk isotopic compositions. These findings may also be relevant for the measurement of other rare isotopologues by mass spectrometry. Copyright (c) 2013 John Wiley & Sons, Ltd.