Validated method for overcoming nitroaromatic thermolability in unmodified GC/MS using molecular isotope dilution mass spectrometry.

Nitroaromatic explosives are frequently detected in soils, sediments, and other environmental samples. Accurate GC/MS quantitation of these thermally labile compounds is a challenge for laboratories that cannot install cold-injection hardware or alter standard instrument configurations (e.g., radiological, hazardous-waste, and many forensic labs). This work presents a validated molecular isotope dilution (m-IDMS) method that both corrects for thermally induced degradation and accounts for deuterium isotope effects on fragmentation by leveraging diverse methodologies and standardized instrumentation for 2-nitrotoluene (2-NT), 2,6-dinitrotoluene (2,6-DNT), and 2,4,6-trinitrotoluene (2,4,6-TNT). Method validation incorporated laboratory prepared spikes, certified reference materials (CRM), and third-party proficiency tests. The CRM and proficiency tests returned acceptable values for all reported nitroaromatic compounds in soil, overlapping with the certified values (95 % CI). Validation achieved parts-per-billion limits of detection, linearity across 3 orders-of-magnitude, 7.8 % (95 % CI) relative mean uncertainty, and no statistically significant bias across the linear range. Compared to calibration curve quantitation, m-IDMS improved sensitivity and uncertainty by 7x and 3x (respectively), expanded the linear range by two orders of magnitude, and decreased mean percent error across the linear range by 2.5x. An isotope effect of 6.46 ± 1.1 (95 % CI) was observed and accounted for in the M+ fragmentation of deuterated 2,6-dinitrotoluene. This work presents an efficient, optimized, and validated method to accurately quantitate thermolabile analytes in constrained operational environments without instrument modification.