Transcript The Chemistry Behind the Breathalyzer

The Breathalyzer™
Presented By Lauren Mercier
What Happens to Alcohol in My
Body After I Have a Drink?
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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
Relating Breath Alcohol to Blood
Alcohol
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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 =
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g Ethanol
x
52.5 mL Breath
2100mL Breath x 100%
1mL Blood
BAC of 0.08 means there are 0.08 g alcohol per
100 mL of blood
The Breathalyzer™
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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
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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…
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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…
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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™
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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
Quartz Lamp
Photocell
Lenses
Filter Wheel
Microprocessor
Examples of Alcohol Detecting
Devices
Intoxylizer® 8000 uses
IR spectroscopy
Intoxylizer® 400 uses
electrochemical fuel cells
Fuel Cell Detectors
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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…
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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
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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). 259261.