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D4 Depressants. D.4.3 Describe and explain the techniques used for detection of ethanol in the breath, the blood and urine. Blood Alcohol Concentration (BAC) is grams of ethanol per 100cm 3 of blood.

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slide2
D.4.3 Describe and explain the techniques used for detection of ethanol in the breath, the blood and urine.
  • Blood Alcohol Concentration (BAC) is grams of ethanol per 100cm3 of blood.
  • Some countries will have a legal limit on the BAC for driving a car. In the U.S. it is often 0.08% (80mg per 100cm3 of blood).
  • Ethanol is volatile, so when the blood stream passes through the lungs, an equilibrium is established and you essentially breathe out ethanol vapours .
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D.4.3 Describe and explain the techniques used for detection of ethanol in the breath, the blood and urine.
  • Road breathalyzers would use acidified potassium dichromate (K2Cr2O7).
  • Recall that potassium dichromate is orange in color. The alcohol acts as a reducing agent and reduces the Cr6+to Cr3+, which turns the color green.
  • However, these tests could notbe held up in a court of law, so more accurate analysis needs to be performed using gas liquid chromatography (GLC) or infra-red (IR) spectroscopy.
gas liquid chromatography
Gas Liquid Chromatography
  • In gas liquid chromatography, a breath, blood or urine sample is obtained.
  • A carrier gas such as N2 is used, and this moves through a column carrying a non-volatile liquid.
  • Different components of the blood or urine are separated based on boiling point and detected.

Unlike the infra-red spectroscopy, this can tell the difference between ethanol and propanone found in the breath of diabetics.

infra red ir spectroscopy
Infra-red (IR) Spectroscopy
  • Modern intoximeters can use infra-red spectroscopy to determine BAC.
  • Infra-red energy is sufficient to cause vibrational motions. The amount of motion depends on the mass of the atoms and the length/strength of the covalent bonds.
  • Since water vapor is in the breath, the O-H peak cannot be evaluated. However, the C-H peak can be evaluated.
  • This is why this intoximeter would not be able to tell the difference between propanone and ethanol.
fuel cell i ntoximeter
Fuel Cell (Intoximeter)
  • In the presence of a catalyst, ethanol is oxidized in the air first to ethanoic acid and then to water and carbon dioxide
  • ethanol + catalystCH3COOHH2O + CO2
  • Oxidation is loss of electrons
  • The fuel cell converts energy released when oxidation occurs into a detectable chemical voltage that can be used to measure ethanol concentration accurately
d 4 4 describe the synergistic effects of ethanol with other drugs
D.4.4 Describe the synergistic effects of ethanol with other drugs.
  • Alcohol taken with aspirin increases stomach bleeding
  • When alcohol is taken with cocaine, cocaethylene is formed, which is far more toxic than either used separately.
  • Alcohol can also be fatal when taken with benzodiapenes (hypnotics) such as valium.
  • Synergistic effect: When the combination of two drugs is more harmful than either drug taken alone.
  • Heath Ledger is thought to have died because of the synergistic effect of mixing prescription drugs.
  • The six drugs he took were medically safe, but mixed together the result was deadly.
d 4 5 identify other commonly used depressants and describe their structures
D.4.5 Identify other commonly used depressants and describe their structures.
  • Valium (diazepam): Sedative drug. Most prescribed drug in the world and used to relieve anxiety and tension.
  • Mogadon (nitrazepam): Common sleeping pill. Also used to control seizures.
  • Prozac (fluoxetine): Anti-depressant drug. Used to treat mental depression. Increases activity of serotonin.