Simultaneous Determination of Twenty-Nine Monocyclic Nitrogen-Containing Heterocyclic Compounds in Particulate Matters of Mainstream Cigarette Smoke by Gas Chromatography-Tandem Mass Spectrometry

Nitrogen heterocyclic compounds in tobacco are an important type of alkaline flavor substances in mainstream cigarette smoke. More than 1 600 nitrogen-containing heterocyclic compounds have been identified in tobacco smoke. Among them, the main monocyclic nitrogen-containing heterocyclic compounds include 116 pentacyclic pyrroles, 365 hexacyclic pyridines, and 106 pyrazines, etc. These semi-volatile monocyclic nitrogen-containing heterocyclic compounds play a significant role in the flavor of the smoke. Therefore, the qualitative and quantitative analysis of monocyclic nitrogen-containing heterocyclic compounds in cigarette smoke is of great significance for the sensory quality evaluation of cigarettes. A new analytical method based on ultrasonic solvent extraction coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) was established for the simultaneous determination of 29 volatile and semi-volatile monocyclic nitrogen heterocyclic components (including pyridines, pyrazines, pyrroles, etc.) in the particulate matters in mainstream cigarette smoke. Under the standard smoking mode, monocyclic nitrogen heterocyclic components in the particulate phase of mainstream cigarette smoke were captured using Cambridge filters. After adding 3,5-dichloro-2-fluoropyridine and 2,5-dibromopyrazine as internal standards, the particulate matters captured by Cambridge filter pads were subjected to ultrasonic extraction with methanol and analyzed by GC-MS/MS using a polar capillary chromatographic column (60 m×0.25 mm, 0.25 μm) under the selective reaction monitoring (SRM) mode. The results showed that the excellent linear relationships (R²≥0.999) were observed over the linear range. The limits of detection (LODs) and the limits of quantification (LOQs) of 29 analytes were 1.0-7.8 ng/cig and 2.0-15.6 ng/cig, respectively. The recoveries and the relative standard deviations (RSDs) of the 29 analytes were 91.9%-108.8% and 0.3%-6.9%, respectively. This method was used to determine 29 single-ring nitrogen heterocyclic components in the total particulate matters of mainstream cigarette smoke from 12 different cigarette brands. Consistent with the analytical purpose, the target analytes were successfully quantified in all tested samples. There are certain differences among the 29 monocyclic nitrogen-containing heterocyclic compounds in the mainstream smoke particles of different cigarette brands, mainly due to the influence of cigarette types, cigarette blending and designs of cigarette auxiliary materials. The contents of 29 monocyclic nitrogen heterocyclic components in the mainstream smoke particulate phase are positively correlated with their tar content of the cigarettes. Eleven components, including pyridine, 2-methylpyridine, 2-methylpyrazine, 3-methylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, 3-ethylpyridine, pyrole, 2-acetylpyrole, pyrro-2-formaldehyde and indole, account for about 80%. Among them, pyridines account for about 60%, pyrroles account for about 15%, and pyrazines account for about 10%. The proposed method is simple, efficient, sensitive, making it suitable for the determination of the release amount of the 29 monocyclic nitrogen-containing heterocyclic compounds in the particulate phase of mainstream smoke from different types of cigarettes. This method provides new technical support for the evaluation of tobacco leaf internal quality, the flavor characteristics of tobacco flavors, the style features of cigarettes, and the optimization of cigarette material design.