1. 5-1 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Spectrophotometry A substance can interact with visible light to produce color Can also interact with invisible radiation Spectrophotometry –measures the quantity of radiation that a material absorbs as a function of wavelength/frequency. –Quantity of light absorbed at any frequency is directly proportional to the concentration of the absorbing molecules. This is known as Beer’s Law.

2. 5-2 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein UVand IR Spectrophotometry Currently, most forensic laboratories use UV and IR spectrophotometers to characterize chemical compounds. The simplicity of the UV spectrum is a great a tool for determining a material’s probable identity –it may not be definitive. heroin caffeine

3. 5-3 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein UVand IR Spectrophotometry The IR spectrum provides a far more complex pattern. Different molecules always have distinctively different infrared spectra –Like a fingerprint

4. 5-4 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein The Spectrophotometer The spectrophotometer is the instrument used to measure and record the absorption spectrum of a chemical substance.

5. 5-5 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Mass Spectrometry In the mass spectrometer, a beam of high-energy electrons collide with a material, producing positively charged ions.

6. 5-6 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Mass Spectrometry positive ions decompose into numerous fragments –separated according to their masses. NO two substances produce the same fragmentation pattern.

7. 5-7 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein GC and Mass Spec GC: Separation of different molecules MS: Identification of each molecule according to it’s fragments.

8. 5-8 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein GC and Mass