Quantum cascade infrared laser spectroscopy for real-time cigarette smoke analysis

A compact, fast-response, infrared spectrometer using pulsed quantum cascade (QC) lasers has been applied to the analysis of gases in mainstream and sidestream cigarette smoke. QC lasers have many advantages over the traditional lead salt tunable diode lasers, including near-room-temperature operation with thermoelectric cooling and single mode operation with improved long-term stability. The instrument uses a 36-m, 0.3-L multiple pass absorption gas cell to obtain a time response of 0.1 s for the mainstream system and 0.4 s for the sidestream system. A precision of 10(-4) absorbance units in 1 s is achieved using pulse normalization to reduce pulse-to-pulse intensity variations. Laser line widths (hwhm) of 0.006 cm(-1) at 967 and 0.010 cm(-1) at 1900 cm(-1) are obtained in pulsed operation. With this instrument, we have measured the concentrations of ammonia and ethylene using a QC laser at 967 cm(-1) and nitric oxide using a laser at 1900 cm(-1) in both mainstream and sidestream smoke from two types of cigarettes. A data rate of 20 Hz provides sufficient temporal resolution to reveal the concentration profiles for these gas components during each 2-s puff in the mainstream smoke. In addition, the concentration profiles before, during, and after the puffs are observed in the sidestream smoke. Simultaneous measurements of CO2 are obtained using a nondispersive infrared analyzer, and the emission ratios of the analyte gases relative to the amount of CO2 produced during combustion are calculated using two types of reference cigarettes.