High-precision measurement of chlorine stable isotope ratios

We present an analysis procedure that allows stable isotopes of chlorine to be analyzed with precision sufficient for geological and hydrological studies. The total analytical precision is ≤±0.09%., and the present known range of chloride in the surface and near-surface environment is 3.5‰. As Cl⁻ is essentially nonreactive in natural aquatic environments, it is a conservative tracer and its δ³⁷Cl is also conservative. Thus, the δ³⁷Cl parameter is valuable for quantitative evaluation of mixing of different sources of chloride in brines and aquifers.