Compound specific carbon, hydrogen, and nitrogen isotope analysis of nitro- and amino-substituted chlorobenzenes in complex aqueous matrices

Compound specific isotope analysis (CSIA) is an established tool to study the fate of legacy groundwater contaminants but is only emerging for non-conventional contaminants, e.g., nitro- and amino-substituted chlorobenzenes. Both chemical groups are widely used as feedstock for numerous industrial applications and often found as a mixture in contaminated sites. However, major bottlenecks to apply CSIA for these heteroatom-bearing chemicals are analytical complexities requiring special considerations and potential matrix interferences in environmental samples. We validated CSIA methods for δ13C, δ2H, and δ15N of several analytes from these chemical groups and developed a solid phase extraction (SPE) method to minimize matrix interferences during preconcentration of complex aqueous samples. Method quantification limits of SPE-CSIA for δ13C, δ2H, and δ15N were 0.03-0.57, 1.3-2.7, and 3.4-10.2 μM aqueous-phase concentrations, respectively, using 2 L water. The SPE-CSIA procedure showed negligible isotope fractionation for δ13C, δ2H, and δ15N. In addition, solvent evaporation, water sample storage up to 7 months, and SPE extract storage for 1.5 years did not change analytes’ original isotope signatures. However, to avoid significant δ2H and δ15N fractionation of aminoaromatics, cartridge breakthrough should be avoided and SPE preconcentration must be conducted at pH>pKa+2. Finally, the method was applied at a contaminated site and the measured δ13C, δ2H, and δ15N values showed excellent precision. The methods validated here are the first necessary step towards the application of SPE-CSIA to understand the environmental fate of nitro-and amino-substituted chlorobenzenes in complex aqueous samples.