Alcohol Testing

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Detection of alcohol A person who has a 100 mg/100 mL of alcohol in blood (1 g/L, 1 ppt) is seven times more likely to have a car accident than a sober person (statistically). Deterioration of the ability to drive starts with 30 mg/100 mL (0.3 g/L, 300 ppm). Alcoholics: regularly carry 150-300 mg/100 mL (1.5 – 2 ppt). 400 mg/100 mL: could be fatal. Canada and England: permitted level is 80 mg/100 mL (0.08) Detectability of ethanol occurs 2 min. after ingesting a drink.

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Determination of blood alcohol content (BAC) Alcohol evaporates from the blood passing through the lungs Into the air of the alveoli. Concentration of alcohol vapour in alveoli is about 2100 lower than It is in blood. i.e.: 80 mg of EtOH in 100 mL blood produces 35 ug of EtOH in 100 mL of air.

Alcohol in urine by GC-FID

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Breath alcohol content

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Based on fuel cell technology.

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Fuel cells (in general) 2 electrodes, coated by a finely divided platinum (Pt =catalyst) in an electrolyte • Hydrogen supplied at one electrode, and oxygen at the other • A current is created between electrodes Fuel + oxygen Æ electricity

Fuel cells (cont’d) •Hydrogen is oxidized at anode 2H2 → 4H+ + 4e•+ve Ions travel through electrolyte to combine with oxygen at Cathode •Electrons Travel through an external circuit to reach oxygen O2 + 4H+ + 4e- → 2H2O Net Reaction: 2H2 + O2 → 2H2O

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Fuel cell Anode side: 2H2 → 4H+ + 4eCathode side: O2 + 4H+ + 4e- → 2H2O Net reaction: 2H2 + O2 → 2H2O

Application for BAC and BrAC •1960’s: first reports of application with EtOH as fuel •1970’s: start of commercial use

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Fuel cells for BrAC •Ethanol (breath) =Fuel •O2 from atmosphere •Oxidized to form Acetic Acid

•e- produce electric current proportional to alcohol concentration

BrAC fuel cells – sampling 1) Passive samplers, aka “sniffers” •qualitatively determine presence or absence of ethanol in an area •Pump used to draw in a sample •Possible uses: •schools, unconscious individual, and passenger compartment of car

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BrAC fuel cells – sampling 2) Active sampler – quantitative •Constant sample size, 1mL; controlled by a pump/piston, variance by no more then 0.3% •Amount of ethanol present determines readout

Then

Now (portable)

personal

Coin Operated

BrAC fuel cells – active samplers •successive positive readings likely to cause error in BAC reading •to maintain evidential accuracy, an average instrument allows only 5 positive readings per hour

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BrAC fuel cells – active sampling How accurate are results?? •Breath ~2100x less concentrated than in blood •Standard partition ratio of 2100 •Ratio of ethanol in blood and breath can very between persons, and an individual’s own samplings (range: 1900 2400)

Other factors affecting accuracy •Body temperature •Increase of 1°C increases BAC by 7% •Small difference can put someone over the limit •Exercise •exercise, or hyperventilation will underestimate BAC by ~15%

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