Blood-alcohol measurement with dichromate

The suspect is required to exhale into a solution that wiU react with the unmetabolized alcohol in the breath. The partial pressure of the alcohol in the exhaled air has been demonstrated to be proportional to the blood alcohol level. The solution is an acidic solution of dichromate ion, which is yellow-orange. The alcohol reduces the chromium in the dichromate ion from +6 to +3, the Cr + ion, which is green. The intensity of the green color is measured, and it is proportional to the amount of ethanol that was oxidized. The reaction is ... 

The equation shows that alcohol in the form of ethanol reacts with an orange solution of potassium dichromate to produce a green solution of chromic sulfate. The source of alcohol is the suspect s breath. More alcohol produces a greater color change. The breath analyzer measures this color change and coverts this measurement into an amount of alcohol in the blood. 

Schematic diagram of a breathalyzer. The alcohol in the driver s breath is reacted with a potassium dichromate solution. The change in the absorption of li t due to the formation ofchromiumflll) sulfate is registered by the detector and shown on a meter, which directly displays the alcohol content in blood. The filter selects only one wavelength of light for measurement.

For the determination of ethanol in blood, the alcohol is oxidized with potassium dichromate in nitric acid. The excess of dichromate is measured polarographically. The method is claimed to determine 2-3 per cent ethanol with an accuracy of 0-05-0-3 per cent in the presence of less than 0-6 per cent acetone, provided that the excess of dichromate is not too large. 

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