I lost my father to lung cancer. I have a certain hatred for tobacco, in any form. I was therefore pleased to read a recent article in the American Chemical Society’s Journal of Agricultural and Food Chemistry that outlined a rather scathing report on “alternative” tobacco products. The researchers, a group from Indiana, used head-space sampling / GC-MS to obtain their results. I first used head-space sampling for GC-MS as a first year graduate student, fourteen years ago. It’s a powerful technique for analyzing any product that has volatile components.
Organic molecules are those which are largely comprised of carbon atoms linked to each other. Natural materials such as tobacco plants are organic in nature, and are therefore full of organic molecules. If the molecule is relatively small – say, less than 20 carbon atoms in size – it isn’t “heavy” enough, in terms of it’s intermolecular attractions, to avoid evaporating into the air. Chemists such as myself call these small moleculars VOCs, or volatile organic components / compounds. Nicotine is a VOC and is the molecule primarily responsible for tobaccos addictive nature. There are hundreds of other volatile organics present in a sample of tobacco, of course. There are also many hundreds of “heavy” organic components in tobacco that don’t easily volatilize into the air above them. Attempting to analyze a sample of dry tobacco is difficult because of all the plant fibrous components that don’t have an appreciable vapor pressure.
The primary technique used by chemists to analyze an unknown sample is something called mass spectrometry (MS). I’ve analyzed thousands of compounds using MS over the years, and I’m always impressed by the wealth of knowledge you can obtain. Mass spectrometry gives you an extremely accurate and precise value for the molecular weight of a compound. With that data, you can then accurately assign a chemical formula to the compound, and by using the various fragmentation peaks you can also make educated guesses as to the precise molecular skeleton. However, MS has it’s limitations. You have to introduce a single compound at a time into the instrument, otherwise you just have multiple spectra overlying each other, which can be incredibly confusing. Also, most mass spectrometers can only analyze a compound if it’s in a vapor state; liquids and solids aren’t useable. Therefore, most MS instruments use a sample injection point that’s red hot. The injected samples immediately volatilize and then are carried on a flow of helium through something called a chromatography column. This technique is known as GC, or gas chromatography. It separates different chemicals that are present in a stream of vapor and lets them filter into the MS instrument one at a time, so that pure spectra are obtained.
With tobacco and other solid products, there is always a concern that the sample that is injected does not accurately represent the solid from which it was obtained. If you take a plug of tobacco and swish it around in a water or some other solvent, chances are it won’t completely dissolve. If you then analyze that liquid using GC-MS, you may obtain some results but you have no idea what might be present in the residual solid that you leave behind. To avoid this difficulty, chemists have developed a technique called headspace sampling. The material is gently heated on a hot plate, and the volatile organic chemicals that rise up from the sample into the “headspace” above the material are collected in a gas-tight syringe. This vapor is then directly injected into the gas chronograph. Since the small, light molecules are the ones of interest to chemists analyzing for organic components, this method of sampling accounts for all the important compounds and also is very easy to perform. I’ve used it dozens of times and it’s attractive both for it’s power and for it’s ease of use. In the journal article I read that discussed tobacco alternatives, chemists from Indiana obtained “alternative” tobacco products such as sticks and “tabs” and heated them over a hot surface. The vapors were then collected and injected into a GC-MS.
The results were very interesting. Many organic flavoring agents were seen such as cinnamaldehyde and ethyl citrate. These are low molecular weight aldehydes and esters and are common in consumer food products. Also present, not surprisingly, was nicotine. It was present in high amounts, in some cases higher than found in most tobacco products. While an argument could be made that these materials were an alternative to tobacco (in that they were an alternative way of obtaining nicotine to feed an addiction), they are not in any way safer over the long run. The levels of nicotine (which is itself a powerful poison) were high enough to ensure a continuing tobacco addiction. A consumer who viewed these products as a “safer” tobacco, something they could use instead of cigarettes and perhaps to lessen their addiction and quit, would be in for a nasty surprise. The article was a classic example of how chemistry can cut through the marketing hype and popular misconception surrounding such products.
The source of this article can be found at:
Rainey, C.L. “Chemical characterization of dissolvable tobacco products promoted to reduce harm”. Journal of Agricultural and Food Chemistry 2011, 59, 2745-2751.