Revealing the Spatial Distribution of Chemical Substances Intercepted by Filter Rods in Flue Gas Based on Laser Ablation-Carbon Fiber Ionization Mass Spectrometry Imaging

Cigarette filter rods play a critical role in trapping harmful chemical components in mainstream smoke. However, conventional analytical methods such as gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) require destructive sample extraction and can only provide average concentration data, failing to reveal the in situ spatial distribution of retained chemicals, which is essential for understanding complex filtration mechanisms and optimizing filter design parameters. Computational fluid dynamics (CFD) simulations, while offering visual insights into airflow patterns, often deviate from actual experimental results owing to inherent simplified assumptions. To address these limitations, this study presented a novel analytical approach based on laser ablation-carbon fiber ionization-mass spectrometry imaging (LACFI-MSI) to visualize the molecular-level spatial distribution of smoke components within filter rods. The LACFI-MSI system integrates a 450 nm laser ablation unit, a carbon fiber ionization source with dual ionization mechanisms, and a Waters SYNAPT XS quadrupole time-of-flight high-resolution mass spectrometer. A neural network-based data fusion algorithm was developed to fuse low-resolution mass spectrometry images with high-resolution optical images, markedly improving the spatial resolution of MS imaging from 250 μm to 50 μm while maintaining quantitative accuracy (average relative error <5%, R²>0.9 for key components such as nicotine). Laser-perforated filter rods with four ventilation rate gradients (22.14% to 70.37%) and specially-shaped hollow filter rods were analyzed following ISO 3308:2012 standard smoking conditions. A total of 34 characteristic smoke constituents belonging to 10 chemical classes (i.e., alkaloids, pyridines, pyrroles, pyrazines, terpenes, aromatics, amides, phenols, organic acids, and furans) were successfully identified and imaged. The results demonstrated that laser perforation profoundly altered both the retention efficiency and distribution patterns of smoke chemical constituents. With increasing ventilation rate, the overall retention density of target analytes decreased significantly, especially at ventilation rates above 50%. A distinctive “ring-shaped enrichment” phenomenon was observed along the edges of laser perforations for pyrroles, terpenes, pyridines, and phenols, which can be attributed to the combined effects of material structural changes and local airflow eddies. In contrast, specially-shaped hollow filter rods exhibited a more uniform chemical distribution with reduced ring-shaped enrichment, indicating improved filtration efficiency through optimized airflow pathways. This method features simple sample preparation, high stability, and excellent spatial resolution. It provides a powerful tool for evaluating the performance of novel filter rods and elucidating their retention mechanisms, offering valuable guidance for the design of next-generation cigarette filters with enhanced capacity for removing harmful components.