Comment on “Freezing Point Mixtures of H216O with H217O and Those of Aqueous CD3CH2OH and CH313CH2OH Solutions”

In a recent article, Kiyosawa [J. Solution Chem. 33, 323 (2004)] reports that the freezing points of isotopic mixtures of ordinary water and ¹⁷O enriched water show an unexpectedly large linear dependence on the concentration of H₂¹⁷O. Surprisingly, the constant of proportionality to the H₂¹⁷O concentration is nearly five times larger than that of H₂¹⁸O found in earlier studies by Kiyosawa [J. Solution Chem. 20, 583 (1991)]. We show that the H₂¹⁷O result is not consistent with other data or models. For example, a recent determination of the triple point temperature dependence on isotopic composition in naturally and artificially depleted waters [White et al. in Temperature, Its Measurement and Control in Science and Industry, Vol. 7, D. C. Ripple, Ed., AIP CP 684, 221–226 (2003)] is consistent with the H₂¹⁸O and D₂O results from Kiyosawa (1991) [White and Tew in Report of the 22nd Meeting of the Consultative Committee for Thermometry, Document CCT/03-21, BIPM, Severes, France, 2003] but is inconsistent with the H₂¹⁷O results from Kiyosawa (2004). Additionally, the results from Kiyosawa (1991) are close to what would be found in ideal solutions for those isotopic forms, whereas the H₂¹⁷O proportionality from Kiyosawa (2004) is about 10 times larger than similarly predicted. One possible explanation is that the original ¹⁷O enriched water sample contained a small amount of D₂O, and the sample, if available, should be subject to isotopic analysis to help resolve these inconsistencies.