10.3 Notes

Breath Test Instruments

Objectives

Understand the concepts of infrared and fuel cell breath-testing devices for alcohol testing.

Why not draw blood at the scene?

Drawing blood from vein is not convenient

Transporting suspect to have blood is costly and time-consuming

Breath analysis is useful, rapid, and accurate

The Breathalyzer

Developed in 1954 by R. F. Borkenstein

(of the Indiana State Police) Phased out during the 1990’s Collects and measures content of

alveolar breathApproximately 52.5 mL collected (1/40 of 2100 mL)

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How does it work Individual breathes into tube that passes to a

glass ampoule Ampoule contains potassium dichromate and

silver nitrate in sulfuric acid and water Alcohol dissolves dichromate solution and is

oxidized to acetic acid

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The amount of potassium that is destroyed is measuredRelates to the amount of alcohol

present in breath Beer’s Law is employed =

quantity of light absorbed by potassium dichromate is directly proportional to its concentration Potassium dichromate is yellow

absorbing light in the 420 nm range

Breathalyzer is basically a spectrophotometer

Breathalyzers – Recent Technology

Using infrared light absorption and/or fuel cell Passes breath into a chamber

Must capture deep lung breath and therefore collects 1.1-1.5 liters of breath blown for minimum of 6 sec.

Contain a slope detector to ensure the breath is alveolar by sampling breath concentration of alcohol continuously

Infrared light aimed through filter selected at a wavelength of light that alcohol will absorb

Light interacts with alcohol thereby diminishing its intensity Measured by photoelectric detector

Signal proportional to concentration of alcohol in breath

Can be used to direct a second infrared beam for detection of substances that are not alcohol

Fuel cell

Converts alcohol (fuel) and an oxidant (air) into an electrical current which converts alcohol to acetic acid and generates a current

Current proportional to quantity of alcohol in the breath