Nitrogen Isotope Analysis of Aliphatic and Aromatic Amines by GC-C-IRMS and the Application for Tracing Atmospheric...

Compounds-specific stable isotope analysis (CSIA) is an advanced tool for assessing the sources and fates of organic amines in environments. The use of gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) remains constrained by the thermal stability, high polarity, and the typically low environmental concentrations of organic amines.

The development of suitable derivatization strategies for polar organic amines can broaden the applicability of GC-C-IRMS. To establish a nitrogen stable isotope analytical method for polar organic amines in the atmosphere, derivatization with isobutyl chloroformate (IBCF) reagent was adopted. Method performance was evaluated using six aliphatic amines and three aromatic amines.

The derivatization method demonstrated good reproducibility, high linearity, and no detectable isotopic fractionation. Accurate and precise nitrogen stable isotope measurements were achieved using the IBCF derivatization reagent. Deviations of δ¹⁵N values from reference measurements obtained by elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) were small (< 0.3‰) and within the typical uncertainty of GC-C-IRMS (< 0.6‰). Method detection limits (MDLs) for the nine organic amines ranged from 2.06 to 4.12 nmol N injected on column.

The applicability of the developed method was demonstrated through analysis of atmospheric methylamine (MA). The measured δ¹⁵N values of MA varied significantly across sources, ranging from -11.6‰ to -9.1‰ for vehicular exhaust, -20.2‰ to -15.7‰ for coastal samples, and -26.7‰ to -22.2‰ for municipal solid waste sanitary sources, indicating that δ¹⁵N values effectively distinguish MA sources.