Analysis of pyrolysis component variations in three azo compounds using headspace gas chromatography-mass spectrometry (HS-GC-MS).

As industrial explosive hazardous chemicals, 2,2'-azobis(2-methylpropionitrile) (AIBN), 2,2'-azodi(2-methylbutyronitrile) (AMBN) and 2,2'-azobis(2,4-dimethyl)valeronitrile (ABVN) have caused multiple explosion accidents. In this study, headspace gas chromatography-mass spectrometry (HS-GC-MS) was used to analyze the differences in pyrolysis products of these compounds under gradient temperatures from 60 to 150 °C and aerobic conditions, aiming to provide methodological support for microphysical evidence identification in forensic science. The results showed that with the increase of temperature, the chromatographic peak areas and numbers of the three compounds generally increased. Violent reactions occurred at 80-90 °C, and the reactions ended at approximately 150 °C. Through mass spectrometry matching, retention index (RI), and fragment ion verification, 40 pyrolysis products (including nitriles, ketones, etc.) were identified, among which some products appeared specifically in certain temperature intervals. Twelve differential components (VIP ≥ 1, p < 0.05) were screened out by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA), and the Fisher discriminant model constructed based on these components achieved a 100% classification accuracy for unknown samples. This study reveals the temperature dependence and species specificity of the pyrolysis behavior of azo compounds, provides a novel pyrolysis product fingerprint-based analytical method for the forensic identification of trace evidence at explosion scenes, and is expected to improve the traceability accuracy of hazardous chemicals in complex scenarios.