Recommendations and Protocols for the Use of the Isotope Ratio Infrared Spectrometer (Delta Ray) to Measure Stable Isotopes from CO₂: An Application to Volcanic Emissions at Mount Etna and Stromboli (Sicily, Italy)

Figure 3

Raw signal (1 Hz) and overlapped Allan deviation using a fixed range dilution system (yellow tube) obtained for 1800 s of measurements for δ¹³C (a) and δ¹⁸O (b) and with an additional flushing time of 600 s before the measurements of δ¹³C (c) and δ¹⁸O (d). Red values and lines represent the theoretical signal expected from the analyzed sampling bag. “Pop.” represents the gas population defined by the sample gas targeted (with 99% of confidence) whereas “Mix.” represents the gas mixture within the cell and the tubes measured at the beginning of the acquisition (see text for explanations). Dashed square represents the subset of measurements (on a time required to obtain 99% of the precision) used to calculate the average value used for the test of accuracy. Box-and-whisker plots for the deviations of δ¹³C (e) and δ¹⁸O (f) measured values from theoretical values of reference gases used in this study (see Methods and Appendix 1). “MLE” refers to the accuracy of the subset of measurements (with the dilution system) belonging to the population of interest (Pop.) obtained using the maximum likelihood estimator.

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