Petrizzo Daniel A, Young Edward D
Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, CA, 90095-1567, USA.
Rapid Commun Mass Spectrom. 2014 Jun 15;28(11):1185-93. doi: 10.1002/rcm.6888.
Rapid development of the CO2 'clumped-isotope' temperature proxy (Δ47 ) has involved both resource- and labor-intensive analytical methods. We report strategies for measuring Δ47 on a conventional mass spectrometer, with the usual CO2 set of three Faraday collectors while reducing the time devoted to standardization with temperature-equilibrated CO2.
We measured Δ47 in CO2 on a mass spectrometer using only three Faraday cups by 'multicollector peak hopping', directing (46)CO2(+) and (47)CO2(+) ion beams into the Faraday cups normally used for m/z 44 and 45. Δ47 was calculated from the previously measured δ(13) C and δ(18) O values and we then measured (47)CO2(+)/(46)CO2(+). We invoke a protocol for correcting ion-beam intensities for secondary electrons to address common problems with compositional non-linearity and both long- and short-term measurement stability.
Our method eliminates the need for six Faraday cups for measuring Δ47, a possible advantage for many laboratories. In addition, by using a correction based on removing the effects of secondary electrons, we remove the Δ47 dependence on δ(47)CO2. As a result, our methods are robust against mass spectrometer operating conditions.
Δ47 can be precisely measured on mass spectrometers currently employed for measuring δ(13) C and δ(18) O values without significant resource investment. Accounting for ion scatter during measurements of CO2 results in improved external precision and long-term stability, while significantly increasing the machine time available for sample analysis.
二氧化碳“聚集同位素”温度代理（Δ47）的快速发展涉及资源和劳动密集型的分析方法。我们报告了在传统质谱仪上测量Δ47的策略，使用通常的由三个法拉第收集器组成的二氧化碳装置，同时减少了用温度平衡的二氧化碳进行标准化所花费的时间。
我们在质谱仪上仅使用三个法拉第杯通过“多收集器峰跳跃”测量二氧化碳中的Δ47，将(46)CO2(+)和(47)CO2(+)离子束导入通常用于m/z 44和45的法拉第杯中。根据先前测量的δ(13)C和δ(18)O值计算Δ47，然后我们测量(47)CO2(+)/(46)CO2(+)。我们采用一种校正离子束强度以校正二次电子的方案，以解决成分非线性以及长期和短期测量稳定性方面的常见问题。
我们的方法无需六个法拉第杯来测量Δ47，这对许多实验室来说可能是一个优势。此外，通过使用基于消除二次电子影响的校正方法，我们消除了Δ47对δ(47)CO2的依赖性。因此，我们的方法对质谱仪的操作条件具有鲁棒性。
无需大量资源投入，就可以在目前用于测量δ(13)C和δ(18)O值的质谱仪上精确测量Δ47。在二氧化碳测量过程中考虑离子散射可提高外部精度和长期稳定性，同时显著增加可用于样品分析的机器时间。
