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 breath Approximately 52.5 mL collected (1/40 of 2100 mL)

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

 The amount of potassium that is destroyed is measured Relates 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 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