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FORENSIC DRUG ANALYSIS

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Drug Identification• The challenge comes in selecting

analytical procedures that will specifically identify a drug.

• This plan is divided into two phases.–Screening test –Confirmation test

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Preliminary Analysis• An unknown substance may be any

one of a thousand commonly encountered drugs

• The analyst must employ screening tests to reduce these possibilities to a manageable number.

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Confirmation Tests• Employed once screening step is

completed

• Specific test that identifies a drug and excludes all other known chemical substances.

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Confirmation Tests• Chromatography and mass

spectrometry are commonly used by forensic scientists.

• Chromatography is a means of

separating and tentatively identifying the components of a mixture.

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Chromatography: molecules represented by the blue dots have a greater affinity for the upper phase and will be pushed faster by the moving air. The two sets of molecules will separate from each other.

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Confirmation Tests• Mass spectrometry identifies a

specific drug according to the mass of its components.

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(a) Mass spectrum of heroin (b) Mass spectrum of cocaine

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Gas Chromatography (GC)• In GC, the moving phase is actually

a gas which flows through a column.

• The stationary phase is a liquid.

• A mixture will emerge separated into its components after it travels through the column.

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Mass Spectrometry (MS)• In the mass spectrometer, a beam of high-

energy electrons collide with a material, producing positively charged ions.

• These positive ions decompose into fragments, which are separated according to their mass.

• No two substances produce the same fragmentation pattern.

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GC/MS• A direct connection between the GC

column and the mass spectrometer allows each component to flow into the mass spectrometer as it emerges from the GC.

• The separation of a mixture’s components is first accomplished by the GC.

• Then the mass spectrometer will produce a distinct pattern of the substance being examined.

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Left to right, the sample is separated into its components by the gas chromatograph, and then the components are ionized and identified by characteristic fragmentation patterns of the spectra produced by the mass spectrometer.

GC/MS

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Thin Layer Chromatography (TLC)• TLC uses a solid stationary phase usually

coated onto a glass plate and a mobile liquid phase to separate the components of the mixture.

• The liquid will slowly rise up the plate by capillary action causing the sample to become distributed between the stationary phase and the moving liquid phase.

• The distance a spot travels up a thin-layer plate can be assigned a numerical value known as the Rf value.

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(a) In thin-layer chromatography, a liquid sample is spotted onto a gel-coated plate.

(b) The plate is placed into a closed chamber that contains a liquid. As the liquid rises up the plate, the mixture is separated. Substances with a greater affinity for the moving liquid travel up the plate faster.

TLC