 |
Infrared Spectrometry (IR) Breath Analysis |
|
Infrared Spectrometry (IR) Breath Analysis |
Simply put, infrared spectrometry (IR) continues to be the most widely accepted evidential form of breath alcohol testing. There is more case law surrounding the use of IR instruments than any other non-invasive type of alcohol testing analysis. The Intoxilyzer® 5000 is by far the most used evidential breath alcohol tester for collecting evidence in DUI cases.
The Alcohol "Fingerprint"
The basic premise of IR technology is that all things will absorb electromagnetic radiation in a unique and consistent manner. Molecular chemistry tells us that all substances, including the alcohol molecular structure, have a unique and consistent quality. Furthermore, the bond between one atom and another establishes that substance’s sensitivity to various wavelengths of electromagnetic radiation and specifically, to infrared light energy. Since no two substances have the same molecular structure, it is possible to analyze or detect a substance’s presence due to the manner in which that substance will absorb the various wavelengths of the infrared spectrum. This absorption or "sensitivity" is caused by the resonating of the molecular bonds when exposed to the infrared energy. The IR energy is absorbed by these resonating bonds and is depleted. Therefore, it is possible to measure the amount of energy that is used, due to the unique and consistent manner in which it occurs. Since these bonds will resonate to different degrees at different wavelengths of IR light, a "fingerprint" of that substance’s absorption or sensitivity to those wavelengths is created. This fingerprint is most commonly expressed in percent transmittance, which depicts the loss of IR light able to pass through the molecule.
See the Light
When IR light of a particular frequency passing through a chamber with no alcohol present strikes a detector, a certain voltage level is created. This can be called X. As an alcohol sample is introduced into the chamber, some of the IR light is absorbed or attenuated. As the alcohol level in chamber increases, the amount of light able to pass through the chamber and strike the detector decreases. At the end of the sample, a very different amount of light is striking the detector creating a different level of voltage. This new level of voltage can be called Y. If the amount of IR light passing through the chamber with no alcohol present can be determined—X, and the amount of light passing through the chamber with alcohol present—Y—can be determined, the difference between the two will represent the concentration of alcohol in the breath sample.The more alcohol present, the greater the absorption.
In the Intoxilyzer® 5000 and 1400, a quartz lamp generates IR energy which travels through a sample chamber containing the subject’s breath. Upon leaving the chamber, a lens focuses the energy onto a chopper wheel containing up to five narrowband IR filters. The IR energy passed by the filters is focused on a highly sensitive photo detector which converts the IR energy into electrical pulses. A microprocessor then interprets the pulses and calculates the Blood Alcohol Concentration which is then displayed on the instrument.
Unlike other testing methods, the Intoxilyzer® 5000 and 1400 utilize features that allow only for the analysis of a subject’s "deep lung" air. They will not give false positives that might result from alcohol being present only in a subject’s mouth (such as might be present with some mouthwash or other confectionery products).
© Copyright 1998, 1999, CMI, Inc.
One of the MPD Companies
316 E. 9th St.
Owensboro, KY 42303 USA
1-866-835-0690
CMI, Inc. is an employee-owned company.