11.3.1 Presumptive Testing

In general, all chemical evidence is treated as 'unknown.' For this reason, the analysis begins with presumptive tests. These are tests that are used to guide the analysis and eliminate compounds (or classes of compounds) from the pool of candidates. They are often quick tests, so several can be performed in a short period of time. Examples of presumptive testing include:

• Books for the comparison of logos and packaging, such as
  • The Drug Identification Bible
  • Physicians Desk Reference
  • DEA Logo Index
    

• Chemical Color Tests are chemical reactions that produce a color change to determine possible chemical class or drug type. There are many such tests given in Isolation and Identification of Drugs by E.G.C. Clarke. Some of the more common ones are:
  • Cobalt thiocyanate (cocaine and other 'caines)
  • Marquis (general purpose, produces a wide range of colors in a variety of samples)
  • Modified Duquenois Levine (cannabinoids)
  • Dille-Kopanyi
  • Van Urk
    

• Microscopic Examination is used to view features, such as crystal shape and bifringence, of crystals precipitated from certain reagents.
• GC, TLC, LC, HPLC and other chromatographic retention data
• Any additional physical properties, such as
  • melting or boiling point
  • color, consistency, texture, etc.
  • solubility in various solvents or reagents
  • density
  • odor (measured with care, of course)
    

• Ultraviolet or visible spectrum
• Miscellaneous chemical tests, such as precipitation from certain reagents