DRUG TESTING17 February 2015

Vocab Review

What is the difference between a presumptive test and a confirmatory test?

• Presumptive tests have high false positives; they indicate that a substance may be present.

• Confirmatory tests do not have false positives; a positive result confirms that a substance really is present.

Why do a presumptive test? • Presumptive tests are usually quick, inexpensive, and can often be

done on the field. This can help guide police and can let them know whether a more time consuming and expensive confirmatory test should be done.

Color Spot TestsProcedure:

• Add a test chemical to an unknown substance. If the drug is present, the chemical will react and change color.

• Different test chemicals for different drugs

• Investigators can use a well plate quickly and easily check for the presence of many different types of drugs

Examples:

• Cobalt thiocynate turns blue when it contacts cocaine (or benadryl)

• Marquis reagent turns purple when it contacts heroin (or medicines with codeine)

presumptive or confirmatory?

Color Spot TestsProcedure:

• Add a test chemical to an unknown substance. If the drug is present, the chemical will react and change color.

• Different test chemicals for different drugs

• Investigators can use a well plate quickly and easily check for the presence of many different types of drugs

Examples:

• Cobalt thiocynate turns blue when it contacts cocaine (or benadryl)

• Marquis reagent turns purple when it contacts heroin or morphine (or medicines with codeine)

presumptive or confirmatory?

Color Spot TestsProcedure:

• Add a test chemical to an unknown substance. If the drug is present, the chemical will react and change color.

• Different test chemicals for different drugs

• Investigators can use a well plate quickly and easily check for the presence of many different types of drugs

Examples:

• Cobalt thiocynate turns blue when it contacts cocaine (or benadryl)

• Marquis reagent turns purple when it contacts heroin or morphine (or medicines with codeine)

presumptive or confirmatory?

IR Spectroscopy• Spectroscopy involves passing a beam of light through a

substance and recording how much light is transmitted through the substance.

• Light that is not transmitted must have been absorbed by the substance.

• Infra-red (IR) light is used to analyze drugs because IR light occurs at the right frequencies to excite the bonds between molecules. When the bonds are excited, the light is absorbed.

• The absorption / transmission patterns are unique to the chemical since the combination of bonds in a chemical are unique.

Vibrating molecule

Sample IR spectra - cocaine• X axis are wave numbers (spatial frequency) of light waves• The overall shape of the spectra and the absorbance peaks

are compared to determine the identity of a chemical

What is the relationship between transmittance and absorbance?

100-TRANS = ABS

What are the major absorbance peaks for cocaine?

1282.3, 1713.6, etc.

More IR Spectra

Why do chemicals have unique IR spectra?

Because the collection of bonds is unique – though chemically similar compounds will have similar spectra

Is IR-Spectroscopy a presumptive or confirmatory test?

confirmatory

GC – Mass SpectrometryThis machine combines two procedures to analyze chemicals:

1) Gas chromatography (GC)

2) Mass spectrometry (MS)

Gas chromatography is used first to separate a mixture into its components.

• The mixture is vaporized into gases

• The gases travel through a long tube to the MS machine.

• The different components separate by time according to how easily each is vaporized and how quickly each travels.

GC – Mass SpectrometryThe mass spectrometer is then used to produce the mass spectrum of each component gas.

• Each gas is blasted with electrons to ionize it – break it into smaller ions.

• The mass / charge ratio of each ion is measured (m/z).

• The mass spectra of different chemicals are nearly unique (there are a few VERY similar chemicals that cannot be differentiated via GC-MS, such as. stereoisomers)

Watch me!

Presumptive or confirmatory?

Confirmatory – at least for very closely related compounds

Quick ReviewWhat is actually measured in each of the three tests discussed?

Spot color tests – looking for color change, indicates a chemical reaction has taken place

IR spectrophotometry – measure absorbance of energy (light) by the bonds in a molecule

GC-MS – measures the mass and charge of ions produced when a chemical is first separated then ionized.

Most forensic investigations will utilize two of the three tests. Why use two tests? Which two would you use?

Use spot color test first because it is quick and cheap. Use EITHER IR spectrophotometry or GC-MS to confirm.

EXIT TICKET

Closure• What were our objectives, and what did we learn?• What was our learner profile trait and how did we demonstrate it?• How does what we did today tie to our unit question?