GCMS: gas chromatography and mass spectrometry in Forensic Science Applications

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

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)

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

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)

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

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

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

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