Hydrogen isotope fractionation in aqueous alkaline earth chloride solutions

Abstract

The D/H ratio of hydrogen gas in equilibrium with aqueous alkaline earth (Mg, Ca, Sr or Ba) chloride solutions measured at 25°C using a hydrophobic platinum catalyst, was found to be higher than the D/H ratio equilibrated with the applied pure water. The hydrogen isotope effect between such solutions and pure water changes with the molality of the solutions. The order of the D/H ratios in alkaline earth chlorides is found to be BaCl2 > SrCl2 ≥ CaCl2 > MgCl2. The hydrogen isotope effect in the aqueous chloride solutions of Mg, Ca, Sr or Ba ions is significantly larger than that in the aqueous chloride solutions of Li, Na, K or Cs ions. For MgCl2 and CaCl2 solutions, the hydrogen isotope effect is opposite to the oxygen isotope effect. The results are compared with the free energy change of transfer from H2O to D 2O, and are discussed for the vapour pressure ratio of H2O and D2O of CaCl2 solutions. © 2007 Verlag der Zeitschrift für Naturforschung.