HPLC Coupled with Quadrupole Mass Spectrometry in the Forensic Analysis of Cocaine

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Analysis of Cocaine
  • Important for forensic analysis of crime scenes
  • Samples are often found in the form of:
    • An unknown powder (could contain other components)
    • A human specimen
    • Fluids (urine, blood saliva)
    • Hair

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Molecular structure of cocaine
(C17H21NO4) with a molecular
weight of 303.353 g/mol



Reverse Phase High Performance Liquid Chromatography (HPLC)
  • Sample injected using pressurized system
  • Compounds travel through column at different rate
  • Interact with stationary phase
  • Detection
    • Traditionally by UV absorption
    • More recently Mass spectrometry
  • Better identification of unknowns

In reverse phase HPLC:
  • Stationary Phase: small silica particles with long hydrocarbons chains attached (non polar)
  • Mobile Phase: solvent, typically a water/alcohol solution (polar)

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HPLC Column with silica beads composing
the stationary phase

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Typical Silica Bead with hydrocarbon chains



Typical HPLC Results: Red compound is less polar and present in lower quantity than the blue compound

Results in Cocaine HPLC

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HPLC Results for Cocaine.  Peak for cocaine circled in red.

Mass Spectrometry

Ion Source
  • Compound vaporized into gas phase
  • Energy added to ionize the compound
  • Excess energy may also fragment compound
  • Most Common Method for cocaine: electrospray
Mass Analyzer
  • Fragments sorted based on mass/charge ratios
  • Ions detected

Quadrupole Mass Spectrometry

  • Apply voltages to 4 parallel rods
  • Create an electric field
  • Can change voltages to scan through m/z ratios
  • Resonant ions will make it through to the detector
  • Non-resonant ions will be neutralized by hitting rod
  • Quadrupole MS allows distinction of compounds with similar m/z
  • Compounds can also be distinguished by fragmentation patterns
Tandem mass spec (MS/MS)
detect molecular ion
add energy to fragment
detect fragment ions

Diagram of Quadrupole Structure.  Distinguishing features and path
of ions illustrated.

Example MS Results

Mass Spectrometry Results for Cocaine.  Unfragmented circled in bold red;
two resulting fragments of most common fragmentation circled in red.

Applications
Recent Studies


References

Clauwaert, K, et. al.  "The Determination of Cocaine, Benzoylecgonine, and Cocaethylene in Small-Volume Oral Fluid Samples by Liquid Chromatography–Quadrupole- Time-of-Flight Mass Spectrometry.Journal of Analytical Toxiocology.  2004 (28): 655-9.

Dawson, Peter H.  Quadrupole Mass Spectrometry and Its Applications.  Amsterdam: Elsvier Scientific Pub. Co., 1976.

Karch, Stven B.  "Introduction to the Forensic Pathology of Cocaine.
The American Journal of Forensice Medicine and Pathology.  (1991)12: 126-131.

Miller, EI, Wylie FM and Oliver, JS.  
"Simultaneous Detection and Quantification of Amphetamines, Diazepam and its Metabolites, Cocaine and its Metabolites, and Opiates in Hair by LC–ESI-MS–MS Using.Journal of Analytical Toxicology.  (2008) 32: 457-69.

http://www.chemguide.co.uk/analysis/chromatography/hplc.html

http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/MassSpec/masspec1.htm