In order to investigate the puff-by-puff release characteristics of mainstream cigarette smoke, a photo-ionization-time-of-flight mass spectrometry (PI-TOF/MS) method was developed for on-line analyzing seven organic compounds (acetaldehyde, 1, 3-butadiene, acetone, isoprene, 2-butanone, benzene and toluene) in mainstream cigarette smoke. The constant volume sampling of mainstream cigarette smoke was achieved by a constant flow orifice, the smoke was directly introduced into the ion source of PI-TOF/MS through a sampling tube with a heating unit. The results showed that: 1) The intra-day and inter-day repeatabilities were good with the relative standard deviations (RSDs) less than 15%, exclusive of the first and the last puffs, where the deviations were larger due to cigarette lighting and variable puff volume, respectively. 2) The RSDs between the results of 1R5F and 3R4F reference cigarettes determined by this method and the mean test values of CORESTA collaborative experiments were less than 10%. 3) The deliveries of different compounds in single puff differed obviously, as did the deliveries between different puffs. This method is simple, fast, accurate, and suitable for the on-line puff-by-puff analysis of mainstream cigarette smoke.%为了考察卷烟抽吸过程中主流烟气的逐口释放特征，建立了在线分析卷烟主流烟气中乙醛、1,3-丁二烯、丙酮、异戊二烯、2-丁酮、苯和甲苯7种有机物的光致电离飞行时间质谱（PI-TOF/MS）方法。通过标准恒流孔实现卷烟烟气的定量取样，烟气经带加热装置的采样管引入PI-TOFMS离子源内进行分析。结果表明：①方法日内重复性、日间重复性良好，除第1口和最后1口由于点火过程及抽吸容量不同而导致变异较大外，其他口的RSD均小于15%；②1R5F和3R4F参比卷烟的测试结果与CORESTA共同实验测试平均值的相对偏差在10%以内；③不同化合物的逐口释放量存在较大差异，逐口之间的释放规律也不一致。该方法操作简单、快速准确，适合于卷烟主流烟气的逐口在线分析研究。
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