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 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 .

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 not be 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

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) SpectroscopyModern 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.

Infra-red (IR) Spectroscopy

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 + CO2Oxidation 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.

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.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.