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Evidentiary Breath Testing Instruments

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  p375-376

2026-08-15

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Evidentiary Breath Testing Instruments

The Intoxilyzer uses infrared spectroscopy for the measurement of alcohol. The alcohol is trapped in a chamber and infrared light is passed through the sample to a detector. The more alcohol there is in the chamber, the less light gets through to the detector. The intensity of light that reaches the detector (or is absorbed by the analyte) is directly proportional to the amount of substance absorbing the light. Early instruments measured absorbance of alcohol at one wavelength of light only. There were concerns that other substances that may be present in the blood such as ketones or other alcohols could interfere with the measure ment of the quantity of ethyl alcohol, so modern instruments measure the amount of alcohol at two wavelengths, with the added one chosen such that it is relatively insensitive to ketones and other alcohols. Figure 1 is a diagram of the intoxilyzer. Other breath testing instruments in current use include fuel cell-based instruments such as the “intoximeter” and dual IR-fuel cell instruments such as the Draeger 7110. The latter instrument has the advantage of giving two independent readings using two different technologies on the same sample.

FIGURE 1 The Intoxilyzer. This instrument uses IR radiation to measure the amount of alcohol in breath. Only those wavelengths of IR light that are absorbed by alcohol reach the detector.