Alcohol Breathalyzer
Breathalyzer is a device for estimating blood alcohol content (BAC) from a breath sample. Breathalyzer is the brand name of a series of models made by one manufacturer of these instruments (originally Smith and Wesson, later sold to National Draeger),
but has become a genericized trademark for all such instruments. In Canada, a preliminary non-evidentiary screening device can be approved by Parliament as an approved screening device, and an evidentiary breath instrument can be similarly designated as an approved instrument. The U.S. National Highway Traffic Safety Administration maintains a Conforming Products List of breath alcohol devices approved for evidentiary use, as well as for preliminary screening use.
but has become a genericized trademark for all such instruments. In Canada, a preliminary non-evidentiary screening device can be approved by Parliament as an approved screening device, and an evidentiary breath instrument can be similarly designated as an approved instrument. The U.S. National Highway Traffic Safety Administration maintains a Conforming Products List of breath alcohol devices approved for evidentiary use, as well as for preliminary screening use.
Breath analyzers do not directly measure blood alcohol content or concentration, which requires the analysis of a blood sample. Instead, they estimate BAC indirectly by measuring the amount of alcohol in one's breath. Two breathalyzer technologies are most prevalent. Desktop analyzers generally use infrared spectrophotometer technology, electrochemical fuel cell technology, or a combination of the two. Hand-held field testing devices are generally based on electrochemical platinum fuel cell analysis and, depending upon jurisdiction, may be used by officers in the field as a form of "field sobriety test" commonly called PBT (preliminary breath test) or PAS (preliminary alcohol screening) or as evidential devices in POA (point of arrest) testing.
Chemistry
When the user exhales into the breathalyzer, anyethanol present in their breath is oxidized to acetic acid at the anode:
CH3CH2OH(g) + H2O(l) → CH3CO2H(l) + 4H+(aq) + 4e-
At the cathode, atmospheric oxygen is reduced:
O2(g) + 4H+(aq) + 4e- → 2H2O(l)
The overall reaction is the oxidation of ethanol to acetic acid and water.
CH3CH2OH(l) + O2(g) → CH3COOH(l) + H2O(l)
The electrical current produced by this reaction is measured, processed, and displayed as an approximation of overall blood alcohol content by the breathalyzer.
source:
http://en.wikipedia.org/wiki/Breathalyzer
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