Signal correlation in isotope ratio measurements with mass spectrometry: Effects on uncertainty propagation

Here the authors argue that the traditional approaches to uncertainty propagation of isotope ratios in mass spectrometry neglect the statistical dependence (correlation) of isotopic signals. It is shown that, in general, mass spectrometric signals of isotopes are correlated. Hence, the uncertainty of isotope ratios can be accurately propagated from their intensities only if signal correlation (covariance) is considered. The discrepancy between the conventionally propagated (with no correlation included) and observed isotope ratio uncertainties is demonstrated using MC–ICP–MS, ICP–TOF–MS and ICP–Q–MS data. This manuscript describes the uncertainty propagation of isotope abundance ratios and ratios of isotope measurements.