Drug detection and analysis Essential idea A variety of analytical techniques is used for detection, identification, isolation and analysis of medicines and drugs.

Drug detection IR, mass spectrometry and 1H NMR can be used to detect banned or illegal chemicals such as steroids in sport as they function as performance-enhancing drugs.

Detection of steroids in sport Gas chromatography Mass spectrometry

Gas chromatography Used to separate and identify the components in a mixture such as blood and urine. Relies on the different components in the mixture having different affinities for two different phases, a mobile phase (a gas medium) and a stationary phase (made up of a liquid). The different affinities depend on its boiling point/volatility and its solubility in both the gas and the liquid Affinities determine the rate at which it passes through the stationary phase.

Gas chromatography: how? The mixture sample is heated (boiling point) and mixed with the gas phase (solubility) and injected in the gas chromatography column. Each component travels though the column at a rate depending on their volatility and solubility in both phases (affinity). A detector measures the time - retention time - this is amount of time between injection time (t=0 on the gas chromatogram) and the time a component is eluted. The retention time of a component is recorded as peak on the gas chromatogram. The area underneath the peak indicates the concentration of the component.

Gas chromatography The retention times for a variety of compounds are known and the component can therefore be identified although identification can also be completed using the fragmentation pattern obtained using mass spectrometry. (see 11.3)

Gas chromatography

Extraction and purification Differences in solubility in different solvents and different boiling points are two physical properties that are often used in the extraction of a drug from a mixture produced as a result of a synthesis that can contain other products, a solvent and catalysts Extraction is often followed by purification of the drug.

Organic structure and solubility Polarity of the structure of molecules determines their solubility in polar and non-polar solvents. Non-polar molecules have very low solubility in polar solvents such as water but higher solubility in other non-polar solvents. Molecules with a polar structure are very soluble in water but have low solubility in non-polar solvents. Molecules that can hydrogen bond have the highest solubility in polar solvents.

Organic structure and solubility low solubility (non-polar molecules) soluble (dipoles) high solubility (hydrogen bonding) alkanes/alkenes aldehydes/ketones alcohols   carboxylic acids halogenoalkanes amines

Solvent extraction Examples: Extraction of aspirin using ethanol Extraction of penicillin using trichloromethane. The separation can be carried out using a separating funnel.

Fractional distillation: main ideas

Detection of ethanol: breathalyser Only used for detection of ethanol in breath. Ethanol is sufficiently volatile to pass into the lungs from the bloodstream which is why it can be detected using a breathalyzer which contains acidified potassium dichromate(VI), an oxidizing agent. There is a direct relationship between the alcohol content in exhaled air and the alcohol content in the blood. In a positive result (i.e. presence of ethanol) the potassium dichromate changes form orange (Cr (VI) or +6) to green (Cr (III) or +3) as the chromium in the chromate ion is reduced by the ethanol (C = ) and the ethanol itself oxidized to ethanal (C= -1) and ethanoic acid (C=0) . The extent of the colour change corresponds to a particular ethanol concentration.

Detection of ethanol: breathalyser Symbol equations: oxidation: C2H5OH + H2O → CH3COOH + 4H+ + 4e− reduction: Cr2O7 2− + 14H+ + 6e− → 2Cr3+ +7H2O Overall: 3C2H5OH+16H+ +2Cr2O72− → 3CH3COOH+2Cr3++ 11H2O

Detection of ethanol in breath: fuel cell Cell = 2 platinum electrodes and an acid electrolyte; uses electrochemistry. Breath is passed over cell Ethanol is oxidized to ethanoic acid and H2O at the anode releasing electrons that produce an electrical current between the electrodes. At cathode oxygen reduced to water. Overall equation: C2H5OH + O2 → CH3COOH + H2O The voltage of the current can be used to measure the ethanol concentration.