TEMPERATURE-DEPENDENCE OF FRACTIONATION OF HYDROGEN ISOTOPES IN AQUEOUS SODIUM-CHLORIDE SOLUTIONS

The D/H ratios of hydrogen gas in equilibrium with aqueous sodium chlo ride solutions of 2, 4 and 6 molalities were determined within the ran ge 10 to 95-degrees-C, using a hydrophobic platinum catalyst. With eac h of the different sodium chloride concentrations, the hydrogen isotop e effect between the solution and pure water changes linearly with the square of the reciprocal temperature. On the basis of the results for hydrogen isotope fractionation observed in this study, and those of h ydrogen isotope fractionation between pure water and vapor, it is conc luded that the structure of the aqueous sodium chloride solution does not change significantly with temperature. The hydrogen isotope effect is evidently different from the results of vapor pressure isotope eff ects (VPIE) on sodium chloride solutions measured on separated isotope s. The difference between the present work and the VPIE studies is pro bably due to a non-ideal behavior in a mixture of isotopic water molec ules and/or to a H-2O-D2O disproportionation reaction in sodium chlori de solutions. The distinction between the latter two mechanisms can no t be differentiated at present.