Methods for the Stable Isotopic Analysis of Chlorine in Chlorate and Perchlorate Compounds

Abstract

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(II) for chlorate and alkaline fusion-decomposition for perchlorate, allows analysis by standard methods to give highly reproducible and accurate delta37Cl results (0.05/1000, 2 x standard error). Analysis of various compounds from different suppliers yielded delta37Cl values for chlorate samples near to +0.2/1000 (SMOC), but one has within-sample heterogeneity of 0.5/1000, possibly due to crystallization processes during manufacture. Results for perchlorate samples also are generally near +0.2/1000, but one is +2.3/1000 (SMOC). The initial results suggest that both forensic and environmental applications might be feasible.

Microbial Isotopic Fractionation of Perchlorate Chlorine

“…Isotopic analysis of the perchlorate and residual chloride contents of the samples was performed as previously described (2). Briefly, chloride was separated from the perchlorate by precipitation as AgCl 2 , and the perchlorate content of the samples was then quantitatively reduced to chloride by alkaline fusion-decomposition as previously described (2). As before, stoichiometric conversion of the perchlorate to chloride (Ͼ98% yield) was achieved (data not shown).…”

“…Cells were removed by filtration through sterile 0.2-m-pore-size filters under an N 2 -CO 2 -H 2 (75/20/5, vol/vol/vol) atmosphere in an anaerobic glove bag (Coy Laboratory Products, Inc.) and dispensed into previously prepared, clean, sterile, sealed 10-ml serum vials filled with N 2 . Isotopic analysis of the perchlorate and residual chloride contents of the samples was performed as previously described (2). Briefly, chloride was separated from the perchlorate by precipitation as AgCl 2 , and the perchlorate content of the samples was then quantitatively reduced to chloride by alkaline fusion-decomposition as previously described (2).…”

In-Situ Bioreduction and Removal of Ammonium Perchlorate

“…Flashpowders were prepared by the standard analytical method (Ader et al, 2001) outlined below where perchlorate is stoichiometrically reduced (greater than 98% yield) to chloride using alkaline fusion-decomposition. To avoid any misinterpretation with potential intrinsic heterogeneity of some samples, chlorate and perchlorate solutions were prepared using a large aliquot of sample, at least six times bigger than the minimum quantity of powder required to perform one analysis.…”

“…The resulting salt was dissolved in water and acidified with nitric acid. After Ader et al (2001), this technique is quantitative and gives stable isotopic composition measurements with a reproducibility of ±0.10 ‰. Some steps of the procedure were carefully refined to ensure good yields, to avoid any contamination and to reduce a potential isotopic shift during the evaporation step.…”

“…The mixture was heated at 80°C for 10 minutes, and allowed to cool to ambient temperature. After Ader et al (2001), this technique is quantitative and give stable isotopic composition measurements with a reproducibility of ±0.18 ‰. The alkaline fusion method used to reduce perchlorate (Ader et al, 2001) was tested to reduce chlorate as well.…”