Determination of deuterium in brines and in hypersaline aqueous solutions by mass spectrometry using zinc as reducing agent

Abstract

A procedure was developed for the determination of deuterium concentration in brines and in hypersaline aqueous solutions, without the removal of alkaline earth metal cations. Aqueous salt solutions of nine salts, LiCl, NaCl, Nal, Na₂CO₃, KCl, K₂SO₄, CsCl, CaCl₂ and Mg(ClO₄)₂, with molalities ranging from 0.5 to 11.8 mol kg^–1 were prepared by dissolving the dry anhydrous salts in de-ionized water of known isotopic composition. Only 8 µl of sample were required to be reduced with zinc metal at 460 °C in a special glass container equipped with a Teflon stopper, to prepare hydrogen for isotopic analysis. The salts NaCl, Nal, Na₂CO₃, KCl, K₂SO₄ and CsCl required 0.25 g, LiCl and CaCl₂ 0.75 g and Mg(ClO₄)₂ 1.00 g of zinc for complete reduction. Deuterium concentrations in brines containing large amounts of Ca²⁺, Mg²⁺, Cl^– and SO₄^2– ions were measured with an accuracy of ±1‰(1σ). In addition, the deuterium content in Dead Sea water was determined with the same method and gave δD =+ 5.4 ± 0.3‰ using 1.50 g of zinc.