•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.

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•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.

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•Presumptive Tests:

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•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.

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•Confirmatory Tests:

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•Can conclusively identify a substance if performed correctly.

•Have a smaller risk of false positives.

•Cost more.

•Require additional equipment.

•Take longer to perform.

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•Types of Presumptive Tests:

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•Color tests/spot tests.

•Microcrystalline tests.

•Ultraviolet spectroscopy.

•Infrared spectroscopy.

•Microscopic examinations.

•(TLC) Thin layer chromatography.

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•Types of Confirmatory Tests:

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•Gas Chromatography /Mass Spectrometry (GCMS).

•Liquid Chromatography /Mass Spectrometry (LCMS).

•Infrared Spectroscopy.

•Nuclear Magnetic Resonance (NMR).

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For more information about standards and testing procedures, see:

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•National Institute of Justice Law Enforcement and Corrections Standards and Testing Program:

•https://www.ncjrs.gov/pdffiles1/nij/183258.pdf

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•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.”