IR spectroscopy of cigarette smoke

In this experiment the constituents of cigarette smoke in undisclosed brands A and B were analysed using Fourier infrared spectroscopy (FTIR). The smoke from the cigarettes of both brands were tested comparing both the levels of carbon monoxide and methane between both brands and the difference in concentration of these constituents in both the filtered and unfiltered of each of the cigarette brands. The results of this study showed that brand B filtered smoke had less carbon monoxide than brand B unfiltered smoke as well Brand A cigarette smoke which seemed to have relatively the same amount of carbon monoxide in both unfiltered smoke as well as having considerably more carbon monoxide than brand B.

Introduction

Fourier Transform Infrared Spectroscopy is a form of IR spectroscopy which is most commonly referred to as FTIR spectroscopy and is used in analysis of the molecular constituents in a sample that is being processed. Infra red radiation is passed through the sample which hits some of the molecular constituents in the sample which either absorbs the energy or is transmitted back while some radiation completely misses the molecules altogether. This then shows the presence of a substance with absorption peaks which are consistent with frequencies of vibrations between the bonds and the atoms that make up the substance as the data is collected and processed. The amount of the particular constituents can also be picked up using the size of each peak on the display. [4]

Infrared Spectroscopy has been used extensively over the past few years as a means of getting accurate data of samples that are being analysed for their chemical constituents. This software has the ability to recognise every single chemical constituent in a sample that has passed through a spectrometer which is held together by chemical bond, however this means that this particular method also has its limitations as it cannot process monoatomic gases as the atoms in the gas do not form a chemical bonds with each other given that IR spectrometer measures the vibrational energies of the bond lengths it will not show up on the final spectra.

IR spectroscopy has further limitations which involve the speed of the processing of the data where each was processed separately; Ft-IR spectroscopy was developed to address this problem by collecting all the frequencies simultaneously. This was achieved by adding a new device to the original IR spectrometer which is known as interferometer. This device is responsible for taking the signal picked by the IR radiation and converting it into a new signal which is now ‘encoded’. This process again is very quick as it is measured to an order of one second. [4] Unfortunately this signal cannot be interpreted until it is converted once more by the Inferogram, this is accomplished by a mathematical technique known as Fourier Transformation which is performed by the software which then displays the spectra.

Experimental

Before the experiment was carried out the FTIR machine was calibrated according to the measurement of the wavenumber to ensure the accuracy of each trial that was carried out. This was done by using ‘trace expansions’ where the band centres were estimated to be within ~0.1 cm-1 which is about a tenth of the resolution. [2]

Prior to the actual measurements were taken a background spectra was taken with a full cell of air as a control for the experiment. Once this had been done at least three times to ensure accurate data the vacuum line was connected to the cell by the quick fit adapter.

The process was commenced by ensuring all five taps on the pump were closed and turned all the way round, clockwise. Then glass wool was packed into the pipette bulb with care using tweezers to make a cigarette holder. The cigarette was inserted into the holder and the pump was switched on. Both taps one and two were opened (see figure 1). The chosen cigarette for that particular trial was then lit, (for unfiltered cigarettes both Cigarettes brands A and B filters were cut off with a pair of scissors). Tap three was then slowly turned so that it was only slightly opened for just one second which allowed air to flow through the machine and therefore causing the cigarette to burn much more energetically. To ensure that as much sample that could be obtained from the smoke was made possible, a boiling tube was placed over the burning cigarette to collect the smoke that was given off from the burning cigarette butt which is then trapped in the gas cell ready for analysis. Taps 1 was then closed and tap 2 was opened to allow cigarette smoke to pass into the gas cell. Tap 2 was then closed followed straight after that by tap 1. The cigarette was then stubbed out the cell was detached from the vacuum line. Once the sample was analysed by the FT-IR Spectrometer the gas cell was evacuated by being placed in a dessicator. The gas line was also evacuated by turning off the tap for the pump and then venting the gas by turning taps 1 and 4. [2]

This procedure was carried out four times to test both filtered and unfiltered brands A and B to obtain 1275 spectra for each trial.

Filtered Cigarette smoke A in (cm-1): CO (1985, 2325), CH4 (1275, 1675), OH (3000, 3625), CH3CHO (2250, 2525) Benzene (625) [5][7]

Unfiltered Cigarette smoke A in (cm-1): CO (2150, 2200), CH4 (1275, 1675), OH (3000, 3625), CH3CHO (2250, 2525) Benzene (625) [5][7]

Filtered Cigarette smoke B in (cm-1): CO (2150, 2200), CH4 (1275, 1675), OH (3000, 3625), CH3CHO (2250, 2525) Benzene (625)

Unfiltered Cigarette smoke B in (cm-1): CO (2150, 2200), CH4 (1275, 1675), OH (3000, 3625), CH3CHO (2250, 2525) Benzene (625) [5][7]

Discussion and Conclusion

It seems that the overall data that was produced shows that filtered cigarette B smoke was the most harmless cigarette smoke in comparison to its unfiltered counterpart and both the filtered and unfiltered brand A cigarette smoke as it had the lowest levels of carbon monoxide. Even though there were very small errors in the analysis of the data there are still limitations with FT-IR spectrometer such as the large stretches of water which strongly absorbs infra red radiation over other molecules and also the difficulty of pin pointing exactly what each of the chemicals were according to the complex stretches that were displayed on the spectra produced.

However the overall advantages are the speed at which the trials are run as all the frequencies are measured simultaneously rather than separately. The FT-IR is also self calibrating therefore so not have to be constantly calibrated by the user ensuring controlled data. [4] The Spectrometer also does not require a vacuum as the IR radiations is not absorbed by either oxygen or nitrogen.This is why this particular form of analysis is used worldwide in analysis of subastances as IR radiation can be absorbed in all three phases (Solid, Liquid and Gaseous states) therefore making it an accurate and versatile method.

Acknowledgements

My heartfelt gratitude extends to Sam Finlayanson, Lewis Alan Edwards5 for allowing me to use their spectra as part of my results so that I am able to write a complete analysis on the experiment. I would also like to thank Mr Douglas Hamilton for his helpful advice and kind support while carrying out the analysis on pgopher and finally the staff of Bristol Chem labs.

References

1. Intra-puff CO and CO2 measurements of cigarettes with iron oxide cigarette paper using quantum cascade laser spectroscopy, Danielle R.Crawforda, Milton E. Parrisha, Diane L. Geea and Charles N. Harward
2. DLM manual
3. Diagram produced on paint by Miss Abira Sri Satkunasingham
4. Thermo Nicolet pamphlet : Introduction to Fourier Transform Infrared Spectrometry
5. Sam Finlayanson, Lewis Alan Edwards: spectra
6. Abira Sri Satkunasingham: experiment calculations and results (spectra)
7. NIST Web book ( for identifying the stretches)
8. Formation and Analysis of Carbon Monoxide in Cigarette Mainstream and Sidestream Smoke Adams, J.D., Hoffman, D. Wynder, E.
9. Determination of Particle-Size Distribution and Concentration of Cigarette Smoke by a Light-Scattering Method TAKASHI OKADA AND KAZUKO MATSUNUMA Central Research Institute, Japan Monopoly Corporation, Midori-ku, Yokohama, Kanagawa 227, Japan
10. Puff-by-puff and intrapuff analysis of cigarette smoke using infrared spectroscopy by Milton E. Parrish, Jim L. Lyons-Hart and Kenneth H. Shafer
11. THE HITRAN MOLECULAR SPECTROSCOPIC DATABASE AND HAWKS (HITRAN ATMOSPHERIC WORKSTATION): 1996 EDITION
12. Fundamentals of Fourier transform infrared spectroscopy By Brian C. Smith