Drug Analysis

Drug IdentificationScreening or presumptive tests

Spot or color tests

Microcrystalline test—

a reagent is added, producing a crystalline precipitate that is unique for a certain drug

Chromatography

Confirmatory tests

Spectrophotometry

• Ultraviolet (UV)

• Visible

• Infrared (IR)

Mass spectrometry

Screening or presumptive tests only tell that the drug is possibly present.

Confirmatory tests tell that the drug is positively present.

(Screening tests are easier, cheaper, and quicker to use.)

Drug Identification, continued

Presumptive Color TestsMarquis—turns purple in the presence of

most opium derivatives and orange-brown with amphetamines

Dille-Koppanyi—turns violet-blue in the presence of barbiturates

Duquenois-Levine—turns a purple color in the presence of marijuana

Van Urk—turns a blue-purple in the presence of LSD

Scott test—color test for cocaine; blue

ChromatographyA technique for separating mixtures into their components

Includes two phases—a mobile one that flows past a stationary one

The mixture interacts with the stationary phase and separates

Types of ChromatographyPaper

Thin-layer (TLC)

Gas (GC)

Pyrolysis gas (PGC)

Liquid (LC)

High-performance liquid (HPLC)

Column

Paper ChromatographyStationary phase—paper

Mobile phase—a liquid solvent

Capillary action moves the mobile

phase through the stationary phase.

Thin-layer Chromatography

Stationary phase—a thin layer of coating (usually alumina or silica) on a sheet of plastic or glass

Mobile phase—a liquid solvent

Retention Factor (Rf)This is a number that represents how

far a compound travels in a particular solvent.

It is determined by measuring the distance the compound traveled and dividing it by the distance the solvent traveled.

If the Rf value for an unknown compound is close to or the same as that for the known compound, the two compounds are likely similar or identical (a match).

Gas ChromatographyPhases

Stationary—a solid or a viscous liquid that lines a

tube or column

Mobile—an inert gas like nitrogen or helium

AnalysisShows a peak that is proportional to the quantity of the substance present

Uses retention time instead of Rf

for the qualitative analysis

Uses of Gas ChromatographyNot considered a confirmation of a controlled substance

Used as a separation tool for mass spectroscopy (MS) and infrared spectroscopy (IR)

Used to quantitatively measure the concentration of a sample. (In a courtroom, there is no real requirement to know the concentration of a substance. It does not affect guilt or innocence.)

Confirmatory Tests: SpectroscopySpectroscopy—the interaction of electromagnetic radiation with

matter

Spectrophotometer—an instrument used to measure and record the absorption spectrum of a chemical substance

Spectrophotometry

ComponentsA radiation sourceA frequency selectorA sample holderA detector to convert electromagnetic radiation into an electrical signal A recorder to produce a record of the signal

TypesUltravioletVisibleInfrared

Infrared Spectrometry

Material absorbs energy in the near-IR region of the electromagnetic spectrum

Compares the IR light beam before and after it passes through a transparent sample

Result—an absorption or transmittance spectrum

Gives a unique view of the substance; like a fingerprint

Mass SpectrometryGas chromatography has one major drawback: It does not give a specific identification. Mass spectrometry cannot separate mixtures. By combining the two (GC-MS), constituents of mixtures can be specifically identified.

Mass Spectrometry, continuedIn a mass spectrometer, an electron beam is directed at sample molecules in a vacuum chamber. The electrons break apart the sample molecules into many positive-charged fragments. These are sorted and collected according to their mass-to-charge ratio by an oscillating electric or magnetic field.

Mass Spectra

Each molecular species has its own unique mass spectrum.

IR Spectrophotometry and Mass SpectrometryBoth work well in identifying pure substances.

Mixtures are difficult to identify in both techniques.

Both are compared to a catalog of knowns.