Breath Analyzers

From Chempedia

Breath Analyzers Gary Hahn, Amber Esch, Matt Fawley, Nate Habben

Breath Analyzers were created in 1954 by Dr. Robert Borkenstein as an efficient way to determine if a suspected driver was driving impaired, under the influence or neither. Prior to 1954, police officers took blood samples or took urine tests. Both of these proved inefficient since the officer would need samples from the suspect, which is considered an invasion of privacy. Another reason why the breath analyzers where so badly needed was that drunk drivers, who could pass the sobriety tests were still breaking the law with exceeding the legal blood alcohol content (BAC) limit. The safety of the public was in desperate need of breath analyzers ("How Breathalyzers work").

Currently there are three common types of testing for blood alcohol content. The most common test is a breath analyzer, which uses a chemical reaction to test for a color change that corresponds to a respective BAC. Second is the Intoxilyzer which detects alcohol by Infared Spectroscopy. The third main type of alcohol analyzing is the Alcosensor. There currently are the Alcosensor III and the Alcosensor IV; both of which detect a chemical reaction in a fuel cell. This article will discuss the uses of the Breath Analyzer.

Breath analyzers have a pretty simple philosophy behind them. First of all, alcohol that a person may drink gets absorbed into the bloodstream from the mouth, stomach, throat, or intestines. According to Henry’s Law the concentration of gas dissolved in a liquid is proportional to the concentration of gas in the air surrounding the liquid. This can be applied in the bloodstream. The more alcohol there is dissolved into the bloodstream the greater the concentration of alcohol there will be in the air sacs of the lungs. Since ethyl alcohol is so soluble in water, it is absorbed into the bloodstream very easily when consumed. When the blood goes into the lungs, some of the alcohol moves into the air sacs because it is volatile and will evaporate from a solution. The concentration of alcohol in the air is proportional to the alcohol in the bloodstream. 2,100 ml of air has the same amount of alcohol in it as 1 ml of blood ("How Breathalyzers work"). The alcohol found in alcoholic beverages is ethyl alcohol or ethanol. Ethanol has a molecular structure like this:

Ethyl alcohol is a colorless liquid that will boil at 78 degrees Celsius and freezes at -114 Celsius. It is also a very flammable liquid. It has a very small molecular weight and because of this, it is very soluble in water

A breathalyzer is made up of silver nitrate, sulfuric acid, potassium dichromate, and water. Basically, it has two glass vials containing mixtures in each one and a system of photocells to measure the color change of the chemical reaction. The suspect will breathe into the device and the breath sample is bubbled through one of the vials containing the sulfuric acid, potassium dichromate, silver nitrate, and water ("How Breathalyzers work"). (Refer to the figure above for an example of this)

For one vial, the sulfuric acid takes the alcohol from the air into a liquid solution, and then the alcohol reacts with the potassium dichromate to produce chromium sulfate, potassium sulfate, acetic acid, and water. The sulfuric acid reacts as a catalyst, speeding up the process. The Potassium Dichromate ion changes from the reddish-orange to a green Chromium Sulfate. The amount of color change is directly related to the amount of alcohol in the exhaled air. The liquid that has changed colors is then compared to the vial of liquid that was untouched. An electric current is then run between the two liquids in the separate vials and the needle on the breath analyzer will move depending on how much of a difference there is in the two liquids. From the movement of the needle, one can tell how high of a blood alcohol content the person has in their system ("How Breathalyzers work").

Footnotes

Boggan, William, Ph.d. "Alcohol and You." Kennesaw State University. 22 Sept. 2005 <http://www.chemcases.com/alcohol/>.

Freudenrich, Craig C. "How Breathalyzers work." How Stuff Works. 22 Sept. 2005 <http://science.howstuffworks.com/breathalyzer.htm>.

"How Breathalyzers work." Camping Survival. 22 Sept. 2005 <http://shop.store.yahoo.com/campingsurvival/howbreatwor.html>.

Melethil, Srikumaran K. "Breath tests for Blood Alcohol Determination." University of Missouri at Kansas City. 22 Sept. 2005 <http://science.howstuffworks.com/framed.htm?parent=breathalyzer.htm&url=http://www.forensic-evidence.com/site/Biol_Evid/Breath_Tests.html>.