drug analysis. drug identification screening or presumptive tests spot or color tests...
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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.
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