The Chemistry Behind the Breathalyzer

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Drunk Or Sober???
The Breathalyzer
Presented By Lauren Mercier
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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
• 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

CH3CH2OH
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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

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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 BACs above
  legal limit of 0.08
• Involves a wet chemistry reaction, modern
  models employ Infrared spectroscopy and fuel cells

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Breathalyzer Apparatus

• Mouthpiece and thermostat set at 50C /- 3C
• 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

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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

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Chemical Reaction

2 K2Cr2O7 3 CH3CH2OH 8
H2SO4 2 Cr2 (SO4)3 2 K2SO4 3 CH3COOH 11
H2O
AgNO3
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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

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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
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Examples of Alcohol Detecting Devices
Intoxylizer 400 uses electrochemical fuel cells
Intoxylizer 8000 uses IR spectroscopy
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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

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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

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References

• http//science.howstuffworks.com/framed.htm?parent
  breathalyzer.htmurlhttp//nydwi.com/dwiqanda/
• http//www.occid.org/legislation/bac-priority.pdf
• http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
  BioBookRESPSYS.htmlThe20Human20Respiratory20Sy
  stem
• http//science.howstuffworks.com/framed.htm?parent
  breathalyzer.htmurlhttp//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/s
  5p4.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.
•