A thoroughly validated spreadsheet for calculating isotopic abundances (2H, 17O, 18O) for mixtures of waters with different isotopic compositions

Rationale Oxygen and hydrogen stable isotopes are widely used tracers for studies on naturally occurring and laboratory mixtures of isotopically different waters. Although the mixing calculations are straightforward to perform, there are ample possibilities to make mistakes, especially when dealing with a large number of mixed fluids. To facilitate isotope mixing calculations and to avoid computational mistakes, a flexible tool to carry out these calculations is in demand. Methods We developed, in three independent efforts, spreadsheets to carry out the mixing calculations for a combination of waters with different isotopic compositions using the isotope mass balance equation. We validated our calculations by comparison of the results of the three spreadsheets for a large number of test calculations. For all the cases, we obtained identical results down to the 12th to 14th significant digit. Results We present a user‐friendly, thoroughly validated spreadsheet for calculating 2H, 17O and 18O stable isotopic abundances and respective isotope delta values for mixtures of waters with arbitrary isotopic compositions. The spreadsheet allows the mixing of up to 10 different waters, of which up to five can be specified using their isotopic abundances and up to five others using their isotope delta values. The spreadsheet is implemented in Microsoft Excel and is freely available from our research groups' websites. Conclusions The present tool will be applicable in the production and characterization of singly and doubly labeled water (DLW) mother solutions, the analysis of isotope dilution measurements, the deduction of unknown isotope values of constituents for mixtures of natural waters, and many other applications. Copyright © 2015 John Wiley & Sons, Ltd.