Compound-specific nitrogen and carbon isotope analysis of nitroaromatic compounds in aqueous samples using solid-phase microextraction coupled to GC/IRMS

Solid-phase microextraction (SPME) coupled to gas chromatography/isotope ratio mass spectrometry was used to determine the delta N-15 and delta C-13 signatures of selected nitroaromatic contaminants such as the explosive 2,4,6-trinitrotoluene (TNT) for derivation of isotopic enrichment factors of contaminant transformation. Parameters for efficient extraction of nitroaromatic compounds (NACs) and substituted anilines from water samples were evaluated by SPME-GC/MS. delta C-13 signatures determined by SPME-GC/IRMS and elemental analyzer IRMS (EA-IRMS) were in good agreement, generally within +/- 0.7%, except for 2,4-dinitrotoluene (2,4-DNT) and TNT, which showed slight deviations (< 1.3%). Limits of detection (LODs) for delta C-13 analysis by SPME-GC/IRMS were between 73 and 780 mu g L-1 and correlated with the extraction efficiencies of the compounds determined by SPME-GC/MS. Nitrogen isotope measurements by SPME-GC/IRMS were of similar precision (standard deviations < 0.8%) for all NACs except for TNT. delta N-15 signatures matched the reference values obtained by EA-IRMS within +/- 1.3% (+2.5% for TNT), but no systematic trend was found for the deviations. LODs of delta N-15 measurements ranged from 1.6 to 9.6 mg L-1 for nitrotoluenes, chlorinated NACs and DNTs (22 mg L-1 for TNT). The SPME-GC/IRMS method is well suited for the determination of isotopic enrichment factors of various NAC transformation processes and provides so far unexplored possibilities to elucidate behavior and degradation mechanisms of nitroaromatic contaminants in soils and groundwaters.