Chapter 3 Forensic Laboratory Techniques Cengage Learning. All Rights Reserved

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1 Chapter 3 Frensic Labratry Techniques

2 Intrductin Objectives 1. Distinguish between physical and chemical prperties. 2. Describe presumptive and cnfirmatry tests. 3. Cmpare and cntrast different types f micrscpes. 4. Explain hw qualitative analysis differs frm quantitative analysis. 2

3 Intrductin Objectives 1. Differentiate between thin-layer chrmatgraphy, gas chrmatgraphy, and high-perfrmance liquid chrmatgraphy. 2. Calculate R (retentin factr). 3. List and describe three types f spectrscpy. 4. Cmpare and cntrast techniques fr visualizing fingerprints. 5. Describe the structure f DNA. 3

4 Intrductin Vcabulary 1. chemical prperty - prperty f a substance that describes hw it reacts in the presence f ther substances 2. chrmatgraphy - any f several prcesses used t separate a mixture int its individual cmpnents based n their attractin t a statinary liquid r slid 3. cnfirmatry test - test dne t establish with certainty the characteristics f a substance 4. frequency - the number f waves that pass a specific pint within a given time; usually expressed in cycles per secnd r hertz (Hz) 4

5 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 5

6 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. 6

7 Presumptive & Cnfirmatry Tests Presumptive tests allw a field investigatr t screen evidence t reduce the number f pssibilities and t get a preliminary identificatin. (saliva, semen, bld, urine, and vaginal secretins) Cnfirmatry tests are used t make a mre specific identificatin. 7

8 Micrscpy Cmpund Light Micrscpe Mst widely used micrscpe Light surce and multiple lenses Magnifcatin between 40x t 1000x View hair, fibers, and cells 8

9 Micrscpy Steremicrscpe Smetimes called a dissecting micrscpe Light is reflected frm the specimen surface Prduces a three-dimensinal image useful fr dissecting Better surface details Inspect insect larvae, paint chips, and ther small items 9

10 Micrscpy Cmparisn Micrscpe Tw micrscpes cnnected t ne eyepiece Tw samples are visible side by side Useful fr cmparing bullet striatins, fibers, and hair 10

11 Micrscpy Electrn Micrscpes Uses beams f electrns t frm images Magnificatin up t 500,000x Black and white Transmissin electrn micrscpe (TEM) passes electrns thrugh the sample t prduce images f internal structures Scanning electrn micrscpe (SEM) passes electrns ver the surface t prduce a three-dimensinal image 11

12 Analytical Techniques Quantitative analysis results in a measurable amunt Qualitative analysis results in a descriptin r identificatin f the cmpnents 12

13 Chrmatgraphy Paper Separates substances within a mixture based n their physical prperties Substances adhere t slid surfaces r disslve in a slvent differently Cmpare a knwn substance t an unknwn ne 13

14 Chrmatgram R f value R f = Distance substance traveled Distance slvent traveled 14

15 Chrmatgraphy Other Types Passes liquid r gas thrugh a clumn r tube packed with a prus slid material Thin-layer chrmatgraphy (TLC) Gas chrmatgraphy (GC) High-perfrmance liquid chrmatgraphy (HPLC) 15

16 Electrmagnetic Radiatin Light travels in electrmagnetic waves Crest highest pint Wavelength distance between tw cnsecutive crests Frequency hw many waves pass thrugh a pint within a given time perid Search fr latent fingerprints Lcate trace evidence Determine the structure f a mlecule 16

17 Electrmagnetic Spectrum 17

18 Spectrscpy Substances, when heated, emit light at a specific wavelength Spectrscpy analyzes the light emissins t determine what elements are present Detects accelerants and explsive residues 18

19 Spectrscpy Mass spectrscpy cmbined with gas chrmatgraphy t identify atms and mlecules by their masses Atmic absrptin spectrscpy (AAS) measures the amunt f light f a specific wavelength absrbed by atms f a substance Ultravilet (UV) spectrscpy measures wavelengths f light; used t determine the cncentratin f elements in a substance 19

20 Fingerprint-Develping Techniques Fingerprint Databases FBI 20

21 DNA Analysis Dexyribnucleic acid fund in the cells f all rganisms DNA fingerprint is a DNA pattern that distinguishes ne individual frm anther 21

22 Chapter Summary Physical prperties are characteristics that can be bserved and measured withut changing the chemical identity f the substance. Chemical prperties are characteristics that determine the way a substance interacts with ther substances. Presumptive tests screen evidence fr pssible identificatin. Cnfirmatry tests determine the identity f evidence. 22

23 Chapter Summary The cmparisn micrscpe is ne f the mst useful tls in frensic investigatins because it allws fr the side-by-side cmparisn f samples. Quantitative analysis will always prduce a number r a prprtin. Qualitative analysis will always prvide a descriptin r statement. Chrmatgraphy is used t separate a mixture int its individual cmpnents. Wavelength is the distance between peaks f cnsecutive waves. 23