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RATIONALE 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. METHODS We measured Δ47 in CO2 on a mass spectrometer using only three Faraday cups by 'multicollector peak hopping', directing 46CO2+ and 47CO2+ ion beams into the Faraday cups normally used for m/z 44 and 45. Δ47 was calculated from the previously measured δ13C and δ18O values and we then measured 47CO2+/46CO2+. 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. RESULTS 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 δ47CO2. As a result, our methods are robust against mass spectrometer operating conditions. CONCLUSIONS Δ47 can be precisely measured on mass spectrometers currently employed for measuring δ13C and δ18O 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. Copyright © 2014 John Wiley & Sons, Ltd. |
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