1. GCMS: gas chromatography and mass spectrometry
in Forensic Science Applications

2. What does the GCMS do?
Separates complex mixtures of chemicals found in substances found at crime scene
Quantifies the amount of each chemical present in a sample, compared to a standard part of database
Identifies chemicals – determines the unique chemical composition and structure-its fingerprint
Compared to a standard fingerprint

3. volatile liquids (~1L)
Gas Chromatography
Gas
Chromatograph
Sample: mixture of
volatile liquids (~1L)
Gas Chromatogram B E C A
Overview of what a GC can do. ~ microliter injection volume is example only - sould not be construed as definitive
Abundance D 5 10 15 20
Time (minutes)

4. Gas Chromatograph Injection Port Detector Capillary Column Data System
or Recorder
Block diagram of GC.
Carrier Gas
Supply
Oven

5. Typical sample: isolated
Mass Spectrometry O C H 3
Mass
Spectrometer H C C N 3 N C C H C C O N N H
Typical sample: isolated
compound (~1 nanogram)
Mass Spectrum
194 67
109
Horizontal axis (mis)labeled as mass rather than m/z so as to not to confuse them at first. Special molecule for Seattle. nanogram amount is an example only - should not be construed as definitive.
Abundance 55 82 42 94
136
165 40 60 80
100
120
140
160
180
200
Mass (amu)

6. Mass Spectrometer Sample Introduction Data Output Inlet Data System
Source
Mass
Analyzer
Ion
Detector
Block diagram of mass spectrometer.
Vacuum
Pumps

7. Electron Impact Ionization Source + _ _ + e- e- e- _ ~70 Volts
Electron Collector (Trap)
Positive
Ions +
Repeller
Neutral
Molecules
Inlet _ _ + to
Analyzer + + + + + +
EI source e- e- e- _
Electrons
Filament
Extraction
Plate

8. Magnetic Sector Mass Analyzer
ion trajectory
in register
ion trajectory
not in register
(too light) S
Detector
Ion
Source N
ion trajectory
not in register
(too heavy)
Electromagnet

9. Quadrupole Ion Filter resonant ion non-resonant ion _ Detector + + _
Source
DC and AC
Voltages