Infrared diodes reveal cigarette smoke mysteries

17 Jun 2002

A device with two tuneable infrared laser diodes is helping to decode the complex mixture of chemicals in every puff of cigarette smoke.

Researchers at the tobacco manufacturer Philip Morris USA have used an optical smoke analyser to measure very low concentrations of gases like ethylene, ammonia and formaldehyde simultaneously. The analyser, developed by the US company, Aerodyne Research, works by infrared absorption spectroscopy.

"We found that 50% of the formaldehyde from a cigarette is delivered in the first puff. If we could do something about that first puff then we could eliminate a significant portion of the formaldehyde delivered," said Susan Plunkett of Philip Morris USA.

The team also hopes to determine whether hydrazine is present in what a smoker inhales. This highly reactive compound was detected in a 1974 study of smoke but this has never been confirmed in real time, with fresh smoke, by a tuneable laser diode system.

Plunkett says that smoke from tobacco is one of the most complex systems to study because it contains so many different chemicals. "When you have a system with about 3000 compounds which are spread across the gas phase, aerosol phase and solid state, you need good spectral resolution to analyse it."

A tuneable laser diode system gives 1000 times better resolution than that given by Fourier transform infrared spectroscopy. "In essence this spreads out the spectrum so that lines corresponding to different compounds are more free from interference." The laser source also gives a higher infrared intensity than the glow bars in Fourier transform systems. "Fourier transform isn't sensitive enough to see the small quantities of ammonia and formaldehyde present."

Another advantage of a tuneable laser diode system is that it can detect many species simultaneously if they absorb in similar regions of the infrared spectrum. With two diodes, the Philip Morris researchers can potentially study up to eight compounds at once. The system compares the results with those from a database of known parameters to identify the compounds.

Plunkett says that all tobacco companies have research groups but Philip Morris USA is the only one to have a tuneable laser diode system. Its system cost USD quarter of a million.

SH