Breathalyzer

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in the blood ... 

C19-0108. Breathalyzers determine the alcohol content in a person s breath by a redox reaction using dichromate... 

The reaction of alcohol with orange dichromate ions to produce blue-green chromium(III) ions is used in the Breathalyzer test, a test that measures the presence of alcohol in a person s breath. How could a colorimeter be used in this analysis ... 

The police may pull over a driver weaving erratically on the highway on suspicion of drunk driving. A police officer must confirm this suspicion by assessing whether the driver has a blood alcohol concentration over the "legal limit." The "Breathalyzer" test checks a person s breath using a redox reaction to determine blood alcohol concentration. This test was invented in 1953 by Robert Borkenstein, a former member of the Indiana State Police, and a professor of forensic studies. 

In the Breathalyzer test, the subject blows into a tube connected to a vial. The exhaled air collects in the vial, which already contains a mixture of sulfuric acid, potassium dichromate, water, and the catalyst silver nitrate. The alcohol reacts with the dichromate ion in the following redox reaction. 

Figure 3.3 A breathalyzer measures the amount of infrared (IR) energy absorbed by alcohol molecules. In this illustration, IR energy from a lamp (1) travels through a chamber (2) holding the subject s breath. As the IR energy exits the chamber, it is focused by a lens (3), passed through IR filters (4), and then converted into electrical signals (5). A computer (6) receives the electrical signals and computes the blood alcohol concentration.

In Australia there have been discussions as to how to make evidential breathalyzer measurements traceable to national or international standards. The amount of ethanol in a motorist is required by law to be less than a prescribed concentration, for many countries between 0.0 and 0.08 g per 100 mL blood. Recently there has been a move to change legislation to a limit of a given mass per 210 L of breath to avoid arguments about the blood/breath partition coefficient. As with any forensic measurement, metrological trace-ability is a key component of a successful prosecution. At present police buy standard solutions of ethanol in water from certifying authorities, with... 

Figure 7.8. A possible metrological traceability chain for the result of a breathalyzer measurement of a motorist s breath alcohol.

When suspected drunk drivers are tested with a Breathalyzer, the alcohol (ethanol) in the exhaled breath is oxidized to acetic acid with an acidic solution of potassium dichromate ... 

The color of the solution changes because some of the orange Cr2072- is converted to the green Cr3+. The Breathalyzer measures the color change and produces a meter reading calibrated in terms of blood alcohol content. 

Oxidation-Reduction in Blood Analysis Demonstrating the Reaction in a Breathalyzer," J. Chem. Educ., Vol. 67,1990, 263. The oxidation of a primary alcohol by the orange dichromate ion is shown to first form an aldehyde, then a carboxylic acid, and green chromium(III) ion. The use of this reaction, principles of spectrometry, and gas laws in a commercial device for measuring blood-alcohol content are discussed. 

The lungs are the primary site of elimination for gaseous anesthetics and any other compounds that are volatile. For example, certain aromatic hydrocarbons are largely eliminated in the expired air. The major pathway for the elimination of ethanol, of course, is metabolism by the liver. However, approximately 2 percent is eliminated via the lungs. The equilibrium partition coefficient for ethanol between blood and alveolar air in humans is approximately 2100 1. Therefore, the ethanol concentration in end-expiratory air can be measured and multiplied by 2100 (e.g., by the Breathalyzer machine) to provide a fairly accurate estimate of ethanol concentration in the blood. 

LG designs cellular phone that has a built-in breathalyzer for sobriety testing this application is also tested as standard equipment for future automobiles... 

One type of breathalyzer detects whether ethanol is in the breath of a person. Ethanol is oxidized to acetaldehyde by dichromate ions in acidic solution. The dichromate ion in solution is orange, while the Cr + aqueous ion is green. The appearance of a green color in the breathalyzer test shows that the breath exceeds the legal limit of alcohol. The equation is... 

Chemicals present in blood that are gases or possess a high degree of volatility diffuse passively into the alveolar air of the lung until they reach equilibrium. The concentration of these chemicals in the air phase is directly proportional to their concentration in blood, and the latter in turn is in equilibrium with the concentration of the chemicals in the tissues. This phenomenon can be applied to noninvasively monitor the presence and the concentration of gases and volatile substances in blood. A practical example of such application is the indirect measurement of alcohol present in blood by analyzing for ethanol in exhaled air with an instrument known as the Breathalyzer. 

Alcohol determinations at the roadside or at home are typically done with a breath analyzer or breathalyzer. Because of rapid gas exchange and the vapor pressure of ethanol, the concentration exhaled is directly related to the blood alcohol concentration. The blood alcohol concentration is widely used as a criterion for determining whether a person is under the influence of alcohol. Many states have ruled that a blood alcohol level of 0.1% or greater indicates intoxication. 

Many breathalyzers have been developed over the years. This model has proved to be effective. 

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