UncorK - A Monte Carlo simulation tool for calculating combined uncertainties associated with mass bias calibration factors for isotope ratio measurements

A complete uncertainty budget including all relevant uncertainty contributions is one of the requirements for an unbroken traceability chain to the International System of Units (SI). Measured ion intensity ratios need to be corrected for any mass bias effects. Correcting the measured ratios is usually done with mass bias correction factors (K-factors). These can be derived from gravimetric isotope mixtures. The resulting absolute isotope ratios are traceable to the SI, provided the uncertainty contribution stemming from the calibration is also considered. Since the computation of K-factors for even small systems containing only a small number of isotopes is challenging, the uncertainty evaluation is also not a straightforward task. This paper presents a way of calculating the uncertainty associated with calibration factors by applying the Monte Carlo method. An EXCEL-based tool is presented that is capable of performing such uncertainty calculations for systems with up to 12 isotopes. Additionally, two examples are given to demonstrate the application of this tool and to validate it.