•Presumptive Methods in medical and forensic science, also known as presumptive tests, are types of sample analysis which establish that either:
•The sample definitely does not contain a certain substance.
•The sample might contain a substance of interest to the analyst.
•Confirmatory tests are the tests required to confirm the analysis made initially by a presumptive test. Confirmatory tests generally take more time and cost more than simpler presumptive tests; presumptive tests are often made on samples first to see if confirmatory tests are necessary on a sample.
•Presumptive Tests:
•Narrow possibilities and help decide which test to do next.
•Can be used on larger areas at a crime scene.
•Can locate evidence not visible to naked eye.
•Are fairly sensitive.
•Have a higher risk of false positives.
•Confirmatory Tests:
•Can conclusively identify a substance if performed correctly.
•Have a smaller risk of false positives.
•Cost more.
•Require additional equipment.
•Take longer to perform.
•Types of Presumptive Tests:
•Color tests/spot tests.
•Microcrystalline tests.
•Ultraviolet spectroscopy.
•Infrared spectroscopy.
•Microscopic examinations.
•(TLC) Thin layer chromatography.
•Types of Confirmatory Tests:
•Gas Chromatography /Mass Spectrometry (GCMS).
•Liquid Chromatography /Mass Spectrometry (LCMS).
•Infrared Spectroscopy.
•Nuclear Magnetic Resonance (NMR).
For more information about standards and testing procedures, see:
•National Institute of Justice Law Enforcement and Corrections Standards and Testing Program:
•https://www.ncjrs.gov/pdffiles1/nij/183258.pdf
•For color test methods for determination of drugs of abuse.
•The site states that “The purpose of this standard is to establish minimum requirements for color test reagent/kits to detect drugs of abuse and methods of testing the reagents to determine compliance with those requirements.”