Transcript The Chemistry Behind the Breathalyzer
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 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 CO 2 upon exhaling + CH 3 CH 2 OH
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 H 2 SO 4 (50 % by volume) K 2 Cr 2 O 7 (0.025 %) AgNO 3 (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 K 2 Cr 2 O 7 + 3 CH 3 CH 2 OH + 8 H 2 SO 4 2 Cr 2 (SO 4 ) 3 + 2 K 2 SO 4 + 3 CH 3 COOH + 11 H 2 O AgNO 3
If the Suspect Is Drunk…
Ethanol in the breath reduces dichromate ion chromium ion to 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 Quartz Lamp Sample Chamber Lenses Filter Wheel Photocell Microprocessor
Examples of Alcohol Detecting Devices
Intoxylizer ® 8000 uses IR spectroscopy Intoxylizer ® 400 uses 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 ” , 261. Journal of Chemical Education . (1990). 67(3). 259-