The peroxynitrite anion (ONOO-), a major product of the gas-phase interaction between the superoxide radical and nitric oxide, has been detected by ion chromatography (IC) for the first time. IC analyses of cigarette whole mainstream smoke collected in deionized water (DiW), using a Dionex 4500i IC, a Dionex AS11 column, an aqueous sodium hydroxide linear gradient with conductivity suppression from 1-20 mMNaOH, and conductivity coupled with diode array detection, revealed an unknown singly charged anion I incompletely resolved from nitrite. Gradient modification produced baseline resolution of I from nitrite and from a number of additional, previously undetected anions associated with smoke samples. Possible candidates for the unexpected smoke sample anion, including bromide, cyanide, and hydrogen hyponitrite were rejected for possible correspondence with the new smoke species on the basis of concentration range and chemical behavior. Chemical, chromatographic, and spectroscopic evidence supported the assignment of this smoke component as ONOO-. Mineral acid immediately destroyed I in the collected aqueous smoke medium. Both the retention time and the ultraviolet spectrum (UV) maximum at 302 nm for I were identical to those for synthetic peroxynitrite. The smoke from full flavor [28.5-30.4 mg total particulate matter (TPM)] filter cigarettes contained 2.4-3.3 µg/cig of this species. Levels were 4 to 5 times higher, up to 13 µg/cig, in cigarettes with the filters removed.
The low-temperature catalytic oxidation of CO has been reviewed, targeting its possible application to cigarette smoke. The treatment of CO in smoke by using a filter-packed catalyst is extremely complicated by the presence of a variety of chemically active gaseous compounds, a particulate phase, the high velocity of pulsing smoke flow, and ambient temperature. The relevant mechanisms of catalysis and the catalyst preparation variables that could help to overcome these problems are considered. Possible contributors to the overall kinetics that must include variety of diffusion processes were briefly discussed. The chemisorption of O2, CO and CO2 on Pd, Pt and Au and on partially reducible supports, surface reactions and oscillations of the CO oxidation rate were analyzed. The effects of the surface structure and electronic properties of the catalyst support, preparation conditions and presence of a second transition metal on the projected CO oxidation activity of the catalysts in smoke are also discussed. The reviewed catalyst preparation approaches can solve the low-temperature catalyst activity problem. However, more work is required to stabilize this activity of an air-exposed catalyst to provide a necessary shelf life for a cigarette. The greatest challenge seems to be a particular phase - exclusive selectivity that would not contradict with the necessary fast diffusion of gases through the catalyst pores.
AJ Dyakonov, RT Walker, CA Brown, FR Perini, DS Passer, J Guan and EA Robinson
Processes involving or forming phenols during combustion of tobacco were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), mass-spectrometry (MS), X-band electron spin resonance (ESR), and thermocouple (TCT) and infrared thermography (IRT) methods. Thermochemical properties of polyhydroxybenzenes, polynuclear aromatic hydrocarbons (PAHs), and carbohydrates were investigated both individually and when the compounds were embedded in combustible or non-combustible matrices; the compounds were studied in an O2/He atmosphere at temperatures up to 800 °C, with a heating rate up to 60 °C/min. ESR of the mainstream smoke ‘tar’ was performed at temperatures down to -253 °C. The radicals found differed in their magnetic behavior depending on the material studied; this difference was attributed to the presence of relatively unstable isolated semiquinone and/or PAH-type molecules and the more stable quinone-hydroquinone-semiquinone redox complex.
Phenols themselves were found to affect combustion by radical scavenging and initiation. Added carbohydrates introduced diffusion limitations to oxygen. They also affected the combustion temperatures and could intensify the formation of phenols via quinone. Oxidation of PAHs was investigated and enthalpies were determined. These enthalpies decreased from benzo[a]pyrene (BaP) to anthracene, naphthalene and phenanthrene.