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Intoxilyzer and IR Spectroscopy

Page history last edited by Yemen Yang 9 years, 4 months ago

Table of Contents

I. Introduction

II. IR Spectroscopy

III. Intoxilyzer and How It Works!

IV. Intoxilyzer Inaccuracies

V. Further Applications of IR Spectroscopy 

VI. References


I. Introduction

     The infrared (IR) region of the electromagnetic spectrum is the region of light that has a longer wavelength and lower frequency than visible light. This region, which is of lower energy than the visible spectrum, can be divided into the near-infrared, mid-infrared, and far-infrared regions. The near-IR is highest in energy and closest to the visible region, while the far-IR is lowest in energy and farthest from the visible region. The mid-IR region, which falls in between these two ranges, is the range most used by chemists for infrared spectroscopy.1 Infrared spectroscopy is often used for determining the structural properties of chemical compounds but has also become useful for more common applications.


Above is a picture of the electromagnetic spectrum, showing the position of the infrared region relative to visible light.2


Above is a picture of the three divisions of the infrared region: the near-IR, mid-IR, and far-IR.3


     IR spectroscopy can be utilized in various ways in current society, one of which happens on a daily basis on the University of Michigan campus, but is probably not known to most people. The Intoxilyzer breath tester uses IR spectroscopy to test for the amount of alcohol in a person's body. Cool, huh? Regular breath testers can be very sensitive to temperature and very miniscule differences in breathing pattern. Furthermore, there are many common sources of error that could render the tester inaccurate. Countering these problems to a certain degree, Intoxilyzers, which utilize IR spectroscopy to determine the blood alcohol concentration, have been developed. Not only is this far more accurate due to the much greater reduction of error, but Intoxilyzer results are also admissible in court, increasing the ability of our police force to catch drunk drivers. The basics of IR spectroscopy and the way Intoxilyzers work will be discussed further. 


II. IR Spectroscopy

     Molecular vibrational frequencies of molecules lie in the IR region of the electromagnetic spectrum, and they can be measured using IR spectroscopy. In this technique, light of different frequencies is passed through a sample, and the intensity of the transmitted light is measured for each frequency. Infrared spectroscopy is used to measure the vibrations of atoms, from which the structure of molecules can be determined.

     When molecules absorb infrared radiation, the electrons absorb photons of infrared light. The energy from the photons is then transferred to the electrons, which allows them to transition from a ground state to an excited vibrational state. Depending on its structure, molecules absorb different frequencies of IR radiation. In general, stronger bonds and light atoms vibrate at a higher frequency.4 In vibrational, or IR spectroscopy, molecular transitions must follow two selection rules. First, molecules must experience a change in dipole moment. Second, the vibrational transitions can only occur with Δν = ±1, meaning they can only experience a change in vibrational quantum number of 1. A molecule must follow the first selection rule (a change in dipole moment) in order to be IR active because a change in dipole moment occurs as a result of the vibrations caused by absorption of IR radiation.



     There are two types of molecular vibrations: stretching and bending. A molecule can vibrate in many ways within these two categories, and these different vibrations represent the vibrational degrees of freedom for molecules. For molecules with N atoms, linear molecules will have 3N-5 vibrational degrees of freedom, while nonlinear molecules will have 3N-6. For example, a three-atom molecule can vibrate in six different ways: symmetric and asymmetric stretching, scissoring, rocking, wagging, and twisting. For a linear molecule, 2 degrees are rotational and 3 are translational, while the remaining degrees correspond to fundamental vibrations. For a nonlinear molecules, 3 degrees are rotational and 3 are translational, with the remaining also corresponding to fundamental vibrations. For each fundamental vibration, a band will appear in the IR spectrum for a molecule.


Above is a picture of the vibrational energy levels.


Above is an example of an IR spectrum for ethanol. Each peak on the spectrum represents a different type of vibrational transition that occurs in the molecule, and the % Transmittance shows the amount of light that is absorbed and transmitted through each transition. Wavenumbers are a measure of energy, and the peaks occur at different wavenumbers, showing the different types of  vibrational transitions occur at each amount of energy.5


III. Intoxilyzer and How It Works!



     The CMI Intoxilyzer 5000 is a new breathalyzer that uses infrared (IR) spectroscopy, as opposed to the more common redox breathalyzer. The Intoxilyzer works by passing a beam of light through a sample of breath and measuring how much light comes back compared to how much was sent out; light is absorbed by alcohol molecules, so the more light that is absorbed, the higher the BAC level.

When the Intoxilyzer produces a beam of infrared light, it splits that beam into two beams and passes one through the sample containing your breath, and the other through a control (usually a pure form of solution containing no alcohol). The difference between the reports sent back to the detector from the two beams is how the machine calculates alcohol concentration. The Intoxilyzer specifically analyzes how much energy was absorbed at each wavelength.6


The following diagram shows the components of the Intoxilyzer:




A)   Lamp – IR source

B)   Breath input

C)   Breath outlet

D)   Sample Chamber

E)    Lenses

F)    Filter wheel

G)   Photocell

H)   Microprocessor


     A lamp generates an IR beam that passes through the sample chamber and is focused by a lens onto a spinning filter wheel. The filter wheel filters light for the three wavelengths used by the Intoxilyzer.The filter wheel contains narrow band filters specific for the wavelengths of the bonds in ethanol. The light passing through each filter is detected by the photocell, where it is converted to an electrical pulse. The electrical pulse is relayed to the microprocessor, which interprets the pulses and calculates the BAC based on the absorption of infrared light.


IV. Intoxilyzer Inaccuracies with the old and new Intoxilyzer

      Lung Capacity: This has a lot to do with the result reported by the Intoxilyzer. The Intoxilyzer is measuring how much light comes back through a sample of air from your lungs, but alcohol enters the lungs through tiny sacs, which are located in the lower end of the lungs. So the that comes from the top of your lungs has a lower alcohol concentration than the air at the bottom of your lungs. The bigger your lungs, the more air comes from the top of your lungs. The smaller your lungs are, the more you have to dip into the bottom of your lungs. Therefore, people with smaller lungs generally end up with higher Intoxilyzer results. Because women have smaller lungs than men, they usually end up with higher Intoxilyzer results.

     Body Temperature:Temperature can affect Intoxilyzer results. The higher your body temperature, the higher the reading on the Intxoxilyzer will read. This means that women, whose body temperatures can fluctuate during menstruation as much as 7 degrees Fahrenheit, can raise their breath results by up to 25%.

     Diabetics: Diabetics can have in their breath a substance known as ketone bodies. Ketone bodies are naturally occurring molecules in humans, but sometimes diabetics have excess quantities, as do individuals with eating disorders or high fat diets. Ketone bodies absorb light quite similarly to the way alcohol molecules do. Thus, diabetics can have Intoxilyzer test results that read higher than their breath alcohol concentration.7


V. Further Applications of IR Spectroscopy

     While infrared spectroscopy is most commonly used as a technique to determine the structures and properties of molecules in chemistry, it can also be used for a number of other purposes. For example, it is also used in forensic analysis and crime investigation, chemical analysis of pills, and measurement of CO2 concentrations in greenhouses.

     IR spectroscopy can be used to identify substances, which can aid in the identification or location of criminal offenders. For example, it can be used to find a specific car model by subjecting a small piece of chipped off car paint to infrared spectroscopy. Infrared spectroscopy can be used to ensure that the correct balance of ingredients is present in a pill, because an imbalance of chemicals in drugs can be lethal in some cases. In addition, infrared gas analyzers are commonly used to measure the levels of CO2 in growth chambers or greenhouses.

     Infrared spectroscopy is one of the most important techniques in both organic and inorganic chemistry, and its usefulness has been expanded to purposes outside of chemistry. Infrared spectroscopy is beneficial even to those who have never heard of it!



VI. References

1. Infrared Spectroscopy: Theory, http://orgchem.colorado.edu/hndbksupport/irtutor/IRtheory.pdf

2. Visible-Invisible, http://bigfootproof.com/groups/visible-invisible-d2-ranges.html

3. Far Infrared Technology, http://moodmastersauna.com/faq/farinfraredtechnology.html

4. Infrared Spectroscopy, http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Infrared_Spectroscop

5. Introduction to Chemical Bonding: Molecules and the Properties of Bonded Atoms,  http://www.chem1.com/acad/webtext/chembond/cb01.html

6. How Things Work, http://electronics.howstuffworks.com/gadgets/automotive/breathalyzer4.htm

7. The Intoxilyzer 5000EN and You, http://kanslaw.com/intoxilyzer-500en.html.




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