Chapter 3 Forensic Laboratory Techniques Cengage Learning. All Rights Reserved

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1 Chapter 3 Frensic Labratry Techniques 2012 Cengage Learning. All Rights Reserved

2 Objective: Yu will be able t describe the thery f chrmatgraphy. Read the Laci Petersn case n p. 70 Cmpile a list in yur ntebk f evidence that was fund.

3 Where is Laci? 1. Laci Petersn 27 and pregnant, disappeared frm her hme Dec. 24, Grid pattern search alng Dry Creek revealed n evidence 3. FBI jined the investigatin 4. Cncrete pwder fund in Petersn s bat 5. Hair samples tested 6. Laci s bld fund n truck dr 3 Frensic Science II: Frensic Labratry Techniques, Chapter Cengage Learning. All Rights Reserved

4 Intrductin Physical prperties are prperties that can be measured withut changing the identity f the evidence Chemical prperties determine hw a substance behaves in the presence f ther substances. 4 Frensic Science II: Frensic Labratry Techniques, Chapter Cengage Learning. All Rights Reserved

5 Presumptive & Cnfirmatry Tests Presumptive tests allw fr a preliminary identificatin. Saliva Semen Bld Urine Cnfirmatry tests are used t make a mre specific identificatin. 5 Frensic Science II: Frensic Labratry Techniques, Chapter Cengage Learning. All Rights Reserved

6 Analyzing Organic Cmpunds Quality versus quantity Quality identifies exactly what it is Quantity may be imprtant because larger amunts f illegal substances may carry lnger jail time Many times substances are in fact mixtures Drug dealers may cut the drugs This requires a different technique t identify the substance

7 Chrmatgraphy This technique has the ability t purify substances It rips each cmpnent frm mixture and separates them int single cmpnents Thery f chrmatgraphy Chemical substances partially escape int surrundings when: Disslved in a liquid Absrbed int a slid

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9 Disslved in liquid Disslved n a slid Gas chrmatgraphy TLC

10 Thin Layer Chrmatgraphy (TLC) Separatin f mixture is dne by using a statinary slid phase (paper) and mving liquid phase Still based n slubility f each substance in the liquid Substances that are highly sluble mve faster Must run unknwn sample alngside knwns

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12 12 Chrmatgraphy Paper

13 Chrmatgram R f value R f = Distance substance traveled Distance slvent traveled 13 Frensic Science II: Frensic Labratry Techniques, Chapter Cengage Learning. All Rights Reserved

14 Objective: Yu will be able t describe hw gas chrmatgraphy separates substance frm a mixture. D Nw: Take ut yur lab frm Friday Finish calculating R F values

15 Disslved in liquid Disslved n a slid Gas chrmatgraphy TLC

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17 Gas Chrmatgraphy Can separate substances because f differences in slubility in a liquid Frce air t cntinuusly mve in ne directin Gas phase is mving phase, liquid phase is statinary phase The chemical race High slubility means it wants t stay in liquid This makes the highly sluble substance mve slwer

18 Sample injected here Cmpnents f a Gas Chrmatgraph Creates a chrmatgram Inert gas This is heated t keep sample in gas state

19 A B Each peak represents a different substance frm the mixture D Which substance had the highest slubility? C E

20 Mixture f material in marijuana

21 chrmatgrams may als be able t identify substances by cmparing t knwn standards.

22 Objective: Yu will be able t explain hw spectrmeters can be used t specifically identify a substance. D Nw: Take ut the ink lab and pass it frward

23 Mass Spectrmeter As the gas leaves the GC, it enters the MS Within the MS, a beam f electrns is sht at the substance breaking it dwn int fragments These fragments pass thrugh an electric field which separates them by their masses The fragment masses are then recrded n a graph Each substance breaks dwn int its wn characteristic pattern

24 MASS

25 MS f Caffeine

26 Micrscpy Cmpund Light Micrscpe Magnifcatin between 40x t 1000x Specimens need t be translucent View hair, fibers, and cells 26 Frensic Science II: Frensic Labratry Techniques, Chapter Cengage Learning. All Rights Reserved

27 Micrscpy Steremicrscpe Smetimes called a dissecting micrscpe Amunts t being a pwerful magnifying glass Can view paque bjects Inspect insect larvae, paint chips, and ther small items 27 Frensic Science II: Frensic Labratry Techniques, Chapter Cengage Learning. All Rights Reserved

28 Micrscpy Cmparisn Micrscpe Tw micrscpes cnnected t ne eyepiece Tw samples are visible side by side Useful fr cmparing bullet striatins, fibers, and hair 28 Frensic Science II: Frensic Labratry Techniques, Chapter Cengage Learning. All Rights Reserved