Compound specific carbon, hydrogen, and nitrogen isotope analysis of nitro- and amino-substituted chlorobenzenes using solid phase extraction

Compound specific isotope analysis (CSIA) is an established tool to study the fate of traditional groundwater contaminants but is only emerging for non-conventional heteroatom-bearing chemicals. We validated an accurate and precise CSIA technique for carbon, hydrogen, and nitrogen isotope analysis of nitro- and amino-substituted chlorobenzenes. The compounds are widely used as feedstock chemicals for numerous industrial applications and found as transformation products of larger molecules, e.g., pesticides and explosives. We developed a solid phase extraction preconcentration and separation method to apply CSIA to complex aqueous samples. The SPE-CSIA procedure showed negligible isotope fractionation for most compounds. Accurate and precise carbon, hydrogen, and nitrogen isotope analyses were obtained down to aqueous-phase concentrations of 0.03-0.48, 1.3-2.7, and 3.4-10.2 mM, respectively using 2 L water. However, only the amino-substituted chlorobenzenes showed significant deviations of δ2H (>10‰) and δ15N (>0.5‰) from the reference values during SPE if the extraction was conducted at pH below pKa+2 due to the protonation of NH2- functional group. Using a systematic approach, we showed that solvent evaporation, water sample storage for up to 7 18 months, and SPE extract storage for up to 1.5 years did not change analytes’ original isotope signatures. Finally, the method was applied at a contaminated site and the obtained δ13C, δ2H, and δ15N values showed excellent precision. The methods validated in this study are the first necessary step toward the application of SPE-CSIA to understand the environmental fate of nitro-and amino-substituted chlorobenzenes in complex aqueous samples.