Taking the Forensic Science Out of Drug Identification

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Taking the Forensic Science Out of Drug
Identification

• Walter F. Rowe, PhD
• Department of Forensic Sciences
• The George Washington University
• Washington, DC 20052

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Background

• Ion mobility spectrometry (IMS) has found
  widespread use as a screening tool for the
  detection of explosives and drugs
• In four drug cases prosecutors proffered an IMS
  scan as the sole method for the identification of
  cocaine
• In three of the four cases, the analyses of the
  suspected drugs were conducted by US Army
  National Guard personnel, rather than trained
  forensic scientists
• The manufacturers of ion mobility spectrometers
  make the claim in their promotional literature
  that their instruments can detect and identify
  drugs

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Ion Mobility Spectrometry
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Ion Mobility Spectrometry
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Smith DetectionIonscan 400B(http//trace.smithsd
etection.com/products/)

• Features Benefits
• Detect and identify over 40 explosive or narcotic
  substances
• Tested, field proven instrument
• Used daily by Military, AVSEC, Customs,
  Corrections and at high profile facilities
• Simple operation, easy to maintain

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Smith DetectionIonscan 400B(http//trace.smithsd
etection.com/products/)

• Features Benefits
• Detect and identify over 40 explosive or narcotic
  substances
• Tested, field proven instrument
• Used daily by Military, AVSEC, Customs,
  Corrections and at high profile facilities
• Simple operation, easy to maintain

7
GE SecurityItemiser(http//www.gesecurity.com/po
rtal/site/GESecurity)

• Itemiser FX
• The world's first direct transfer trace detection
  instrument simultaneously identifies explosives
  and narcotics directly from a finger imprint.
  With one touch and in a matter of seconds,
  Itemiser FX can detect a broad range of
  contraband without reducing the amount of
  substance available for detection. By sampling
  directly from the finger, the system can
  eliminate the time, cost and staff required with
  sample wipes.

8
GE SecurityItemiser(http//www.gesecurity.com/po
rtal/site/GESecurity)

• Itemiser FX
• The world's first direct transfer trace detection
  instrument simultaneously identifies explosives
  and narcotics directly from a finger imprint.
  With one touch and in a matter of seconds,
  Itemiser FX can detect a broad range of
  contraband without reducing the amount of
  substance available for detection. By sampling
  directly from the finger, the system can
  eliminate the time, cost and staff required with
  sample wipes.

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Detect and Identify

• Analytes can be detectable without being
  identifiable
• Example
• The base peak of an electron impact mass spectrum
  may be detected (signal-to-noise ratio is greater
  than two or signal exceeds three times the
  standard deviation of background signal)
• Other structurally significant ions may not be
  strong enough to be detected

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SWGDRUG and ASTM e30 Guidelines

• The Scientific Working Group for the Analysis of
  Seized Drugs (SWGDRUG) and ASTM Committee e30
  have published guidelines for the analysis of
  seized drugs
• The SWGDRUG Methods of Analysis/Drug
  Identification and ASTM E2329-04 Standard
  Practice for Identification of Seized Drugs
  classify methods of analysis in three categories
  (A, B and C)

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Category A Methods of Analysis

• Validated Category A methods of analysis provide
  the highest level of discriminating power in drug
  identification
• Category A methods of analysis are
• Vibrational spectroscopies (infrared and Raman
  spectroscopies),
• Nuclear magnetic resonance spectrometry (NMR) and
  
• Mass spectrometry

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Category B Methods of Analysis

• Validated Category B methods of analysis provide
  a lower level of discriminating power in drug
  identification
• Category B methods of analysis are
• Capillary electrophoresis
• Gas chromatography
• Ion mobility spectrometry
• Liquid chromatography
• Microcrystalline tests
• Pharmaceutical identifiers
• Thin layer chromatography
• Cannabis only macroscopic and microscopic
  examination

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Category C Methods of Analysis

• Validated Category C methods of analysis provide
  the lowest level of discriminating power in drug
  identification
• Category C methods of analysis are
• Color tests
• Fluorescence spectroscopy
• Immunoassay
• Melting points
• Ultraviolet spectroscopy

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Identification Criteria

• When a validated Category A technique is
  incorporated into an analytical scheme, then at
  least one other technique (from either Category
  A, B or C) must be used
• When a Category A technique is not used, then at
  least three different validated methods must be
  employed
• Two of the three methods must be based on
  uncorrelated techniques from Category B

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Identification Criteria

• If ion mobility spectrometry (a Category B
  method) is used, the analysis of seized drugs
  another Category B method must also be used with
  it

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Ion Mobility Spectrometry
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Ion Mobility Spectrometry
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Ion Mobility Spectrometry

• Sample molecules introduced into the ion mobility
  spectrometer are ionized by beta particles
  emitted by 63Ni
• Ion mobility spectrometers can operate in
  positive ion (drugs) and negative ion
  (explosives) modes
• A voltage pulse applied to the gating grid allows
  a burst of ions to travel down the drift tube to
  the collector electrode

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Ion Mobility Spectrometry

• The ions are accelerated toward the collector
  electrode by an applied voltage
• The ions collide with the molecules of the drift
  gas

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Ion Mobility Spectrometry

• ltvdgt average drift velocity of analyte ion
• K ion mobility constant
• E electric field strength
• q charge on analyte ion
• N number density of drift gas
• m mass of analyte ion
• M mass of drift gas
• O0 diffusion collision integral

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Sample Plasmagram
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Plate Theory

• Ion mobility spectrometry has also been called
  plasma chromatography
• Chromatographic plate theory can be applied to
  ion mobility spectrometry
• G.E. Spangler and C.I. Collins, Anal Chem, 47(3),
  403-407 (1975)
• The higher the number of theoretical plates for a
  separation method the higher the resolution of
  the method

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Calculation of Number of Theoretical Plates (N)

• N number of theoretical plates
• l column length
• h height equivalent of a theoretical plate

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Chromatographic Resolution

• For chromatographic peaks having equal areas, the
  resolution R of two consecutive peaks is given by
• a separation factor for peaks (ratio of
  partition coefficients)
• K2 partition coefficient for second peak

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Number of Theoretical Plates for Ion Mobility
Spectrometry

• Examination of plasmagrams from ion mobility
  spectrometers used in drug cases shows that their
  separations are equivalent to a chromatographic
  separation with 7,000 to 8,000 theoretical plates
• Ion mobility spectrometry separates analytes
  better than packed column gas-liquid
  chromatography but not as well as capillary
  column gas-liquid chromatography

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Comparison of Separation Methods
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Additional Problems

• Having drug exhibits analyzed by technicians who
  are not trained forensic scientists can lead to
  further problems

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Additional Problems

• The seven currency exhibits seized at different
  locations in the suspects home were aggregated
  and analyzed by a single scan

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Conclusions

• The manufacturers of ion mobility spectrometers
  exaggerate the instruments capabilities
• Some end users do not understand the inherent
  limitations of ion mobility spectrometry
• Forensic scientists should be more involved in
  counterdrug programs