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The Chemistry Behind the Breathalyzer

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The Chemistry Behind the Breathalyzer Powered By Docstoc
					  The Breathalyzer™

Presented By Lauren Mercier
         What Happens to Alcohol in My
          Body After I Have a Drink?
   Ethanol is immediately absorbed into the
    capillaries of body tissues and organs
   When it enters the blood stream,
    ethanol is not metabolized and
    remains a separate component in blood
    flow                                           + CH3CH2OH

   As blood flows across alveoli in the lungs,
    carbon dioxide molecules are exchanged
    for oxygen molecules
   Ethanol evaporates from the blood into the
    breath since it is volatile, and is released
    with CO2 upon exhaling
Relating Breath Alcohol to Blood
            Alcohol
   The ratio of breath alcohol to blood
     alcohol is 2100 : 1, so 2100 mL of
    alveolar air contains the same amount
     of alcohol as 1 mL of blood
   Blood alcohol content (BAC) can be calculated
    from the content of alcohol in the breath
    % BAC =     g Ethanol    x   2100mL Breath x 100%
              52.5 mL Breath       1mL Blood
   BAC of 0.08 means there are 0.08 g alcohol per
    100 mL of blood
The Breathalyzer™
   Measures concentration of alcohol in
    breath sample and determines BAC
   Invented by Dr. Robert F. Borkenstein
    of Indiana State Police Department and has been
    on the market since 1954
   Used to prosecute drunk drivers with BAC’s above
    legal limit of 0.08
   Involves a “wet” chemistry reaction, modern
    models employ Infrared spectroscopy and fuel
    cells
Breathalyzer™ Apparatus
   Mouthpiece and thermostat set at 50°C +/- 3°C
   Sample chamber, contains piston that traps 56.5mL
    breath and delivers 52.5mL breath to reaction mixture
   Two sealed glass vials containing reaction mixture
         H2SO4 (50 % by volume)
         K2Cr2O7 (0.025 %)
         AgNO3 (0.025 %)
   Light bulb between glass vials and photocells on either
    side
   Meter connected to electrical output
   Alcohol scale
Collecting the Sample…
   The suspect blows into the mouthpiece and
    their breath travels to a sample chamber
   One glass vial neck is broken (test vial) and
    a glass tube, called a “bubbler”, is inserted
   The operator turns a control knob to
    release the piston and force the sample
    through the bubbler into the test vial
     Chemical Reaction


2 K2Cr2O7 + 3 CH3CH2OH + 8 H2SO4
                                          AgNO3

2 Cr2 (SO4)3 + 2 K2SO4 + 3 CH3COOH + 11 H2O
If the Suspect Is Drunk…
   Ethanol in the breath reduces dichromate ion to
    chromium ion
   The test vial lightens from pale yellow to a
    bleached yellow colour, like weak lemonade
   More light passes through the lightened test vial
    and hits a photocell causing electrical needle on
    meter to move
   The operator turns a knob to balance needle and
    light moves away from test vial
   When the needle is centered the operator reads
    alcohol meter to determine BAC
The Intoxylizer™
   Uses Infrared spectroscopy to detect ethanol (C-O, O-H, C-H, C-C
    bonds)
   IR energy passes through sample chamber containing breath
    sample and then through narrowband IR filter
   Filtered energy focused on photocell detector which converts it to
    electrical pulses
   Microprocessor interprets pulses and calculates BAC
                   Breath Sample In       Breath Sample Out




                              Sample Chamber
                                                                             Photocell

     Quartz Lamp                 Lenses
                                                              Filter Wheel          Microprocessor
        Examples of Alcohol Detecting
                  Devices




Intoxylizer® 8000 uses      Intoxylizer® 400 uses
   IR spectroscopy       electrochemical fuel cells
          Fuel Cell Detectors
   Apparatus consists of two platinum electrodes
    with acidic electrolyte material between them
   Ethanol in breath oxidized at surface of anode
    to give acetic acid, protons, and electrons
   Atmospheric oxygen reduced at cathode to
    give two oxygen atoms
   Protons and electrons from anode travel to
     the cathode and combine with oxygen to
    form water
   Movement of electrons produces a current
    that is proportional to the amount of alcohol in the breath sample
   Microprocessor measures the current and calculates BAC
In Conclusion…
   There are several methods available for forensic
    alcohol testing
   Now there are hand held breath alcohol testers to
    take on site or to parties to decrease the number
    of people who drink and drive
   Results provide evidence in DWI trials
   Results can be inaccurate because of
    temperature changes and varying blood to breath
    ratios
   Tests are non-invasive and fairly accurate but
    require a trained operator
References
   http://science.howstuffworks.com/framed.htm?parent=breathalyzer.
    htm&url=http://nydwi.com/dwiqanda/
   http://www.occid.org/legislation/bac-priority.pdf
   http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookRESPS
    YS.html#The%20Human%20Respiratory%20System
   http://science.howstuffworks.com/framed.htm?parent=breathalyzer.
    htm&url=http://nydwi.com/dwiqanda/
   http://www.craigmedical.com/Breathalyzer_FAQ.htm
   http://www.alcoholtest.com/ecfuel.htm
   http://www.alcoholtest.com/ir.htm
   http://www.druglibrary.org/schaffer/Misc/driving/s5p4.htm
   http://www.lion-breath.com/serv01.htm
   Labianca, Dominick A. “The Chemical Basis of the Breathalyzer: A
    Critical Analysis”, Journal of Chemical Education. (1990). 67(3). 259-
    261.

				
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posted:4/7/2010
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