Accurate experimental determination of the isotope effects on the triple point temperature of water. II. Combined dependence on the 18O and 17O abundances

This paper is the second of two articles on the quantification of isotope effects on the triple point temperature of water. In this second article, we address the combined effects of O-18 and O-17 isotopes. We manufactured five triple point cells with waters with O-18 and O-17 abundances exceeding widely the natural abundance range while maintaining their natural O-18/O-17 relationship. The H-2 isotopic abundance was kept close to that of VSMOW (Vienna Standard Mean Ocean Water). These cells realized triple point temperatures ranging between -220 mu K to 1420 mu K with respect to the temperature realized by a triple point cell filled with VSMOW. Our experiment allowed us to determine an accurate and reliable value for the newly defined combined (18,) O-17 correction parameter of A(O) = 630 mu K with a combined uncertainty of 10 mu K. To apply this correction, only the O-18 abundance of the TPW needs to be known (and the water needs to be of natural origin). Using the results of our two articles, we recommend a correction equation along with the coefficient values for isotopic compositions differing from that of VSMOW and compare the effect of this new equation on a number of triple point cells from the literature and from our own institute. Using our correction equation, the uncertainty in the isotope correction for triple point cell waters used around the world will be <1 mu K.