Government of Ontario

CFS - TIS - Chemistry - Chemical Identification

Centre of Forensic Sciences

Technical Information Sheets

Chemistry


Chemical Identification & Comparison – PDF, 27 kb


Introduction

Chemical identification and comparison cases may involve the following types of investigations: identification of unknown liquids or solids; determining if toxic or dangerous material is present in a matrix such as food or beverage; comparing materials to determine whether or not they have originated from the same source.

Examination

Examinations may include visual or microscopic examination, measuring the physical and chemical properties of the unknown material, and instrumental analysis to assist in determining the identity of the unknown chemical component(s).

For altered materials, the analysis will be done to determine the major components present or the “active ingredient” in a commercial product. For some commercial products the “active ingredient” is present in such small quantities that the analysis will include looking for other components present in larger quantities. The concentration of the different components is not determined.

If a sample is examined to determine whether or not any foreign material is present, it is usually necessary to examine a comparison sample of the material in an identical manner. For example: A case where coffee is believed to have had a cleaning product added to it and the active ingredient in the cleaning product is limonene. The suspected adulterated coffee will be examined for the presence or absence of limonene. A comparison sample such as the suspected bottle of cleaning product from the scene, or a new bottle of the same product in question, will assist with the interpretation and expedite the analysis. A comparison sample of the same coffee in the case that is known not to have any cleaning product in it will also assist in the interpretation.

If a drug is indicated during this examination, the Chemistry Section will consult with the Toxicology Section in order to assess an appropriate examination strategy.

Glossary

Aqueous
An aqueous material is one which is water-based.

Detection limit
The lowest concentration of a material that can be identified using a given method of analysis.

Fourier Transform Infrared Spectroscopy (FTIR)
This instrumental technique is used to characterize the type of material based on its absorption of infrared light. It provides information about the chemical groups present in a molecule.

Gas Chromatography - Mass Spectrometry (GC-MS)
Gas chromatography is a technique used to separate the components of a mixture. The mass spectrometer may be used to identify the components.

Headspace Gas Chromatography - Mass Spectrometry (HGC-MS)
is a technique in which volatile material in a sample is analyzed. A sample of the vapours in the jar or nylon bag is extracted for injection into the GC/MS.

Ion Chromatography (IC)
is used to analyze the ions present in a water-soluble material.

Liquid Chromatography - Mass Spectrometry (LC-MS)
is used to separate (LC) and identify (MS) components of a mixture.

Organic solvent extraction
An organic solvent is a liquid which is carbon based, non-aqueous. Organic solvents may be used to extract a chemical component out of a sample, for further analysis.

Oxidizing
material is one which provides oxygen and can react with other materials. Examples of oxidizing materials include bleach and hydrogen peroxide.

pH
is a measure of whether a liquid is acidic, neutral or basic/alkaline.

Pyrolysis Gas Chromatography - Mass Spectrometry (PGC-MS)

Pyrolysis is a technique in which heat is used to fragment a sample in the absence of oxygen. Gas chromatography is a technique used to separate the components of a mixture. The mass spectrometer may be used to identify the pyrolysis fragments of the sample when combined with PGC. This technique requires that a very small quantity of material be consumed.

Reference Material
A known material analyzed in the same way as the unknown sample in order to identify the unknown material.

Scanning Electron Microscopy - Energy Dispersive X-Ray Analysis (SEM-EDX)
The SEM produces a magnified image of the sample based on the interaction of an electron beam with the sample’s surface. The EDX is used to identify some of the elements present based on the x-rays produced through interactions between the sample and the SEM electron beam.

Vapour
A gas produced by the evaporation of a liquid that may mix with air or other gases.

Volatile
Readily evaporates at normal temperatures and pressures.

X-Ray Diffraction (XRD)
This instrumental technique is used to identify crystalline components of a material based on their interaction with x-rays.