Methods for the stable isotopic analysis of chlorine in chlorate and perchlorate compounds

Chlorate and perchlorate compounds, used as herbicides, solid fuel propellants, and explosives, are increasingly recognized as pollutants in groundwater. Stable isotope characterization would permit both environmental monitoring of extent of remediation and forensic characterization. Stoichiometric reduction to chloride (greater than 98% yield), by Fe(H) for chlorate and alkaline fusion-decomposition for perchlorate, allows analysis by standard methods to give highly reproducible and accurate delta Cl-37 results (0.05 parts per thousand, 2 x standard error). Analysis of various compounds from different suppliers yielded delta Cl-37 values for chlorate samples near to +0.2 parts per thousand (SMOC), but one has within-sample heterogeneity of 0.5 parts per thousand, possibly due to crystallization processes during manufacture. Results for perchlorate samples also are generally near +0.2 parts per thousand, but one is +2.3 parts per thousand (SMOC). The initial results suggest that both forensic and environmental applications might be feasible.