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Breath-alcohol instrumentation

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  312

2026-10-27

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Breath-alcohol instrumentation

The first instruments for breath-alcohol testing employed chemical reactions involving a colour change. Concerns were raised about the specificity and accuracy of these and they have largely been replaced by devices employing the optical absorption of infrared (IR) energy according to Beer’s law making this a quantitative determination. Such instruments include the Camic Datamaster (Camic Ltd, UK) and the Lion Intoxilyzer (Lion Laboratories, UK). Specificity needs to be taken into account when using IR because other volatile organic substances which may be present in breath will also absorb in the IR and may produce a false reading. Examples of such substances include volatiles produced by ketosis and volatile solvents such as toluene and paint thinners which may be present via solvent abuse, the workplace or home decorating and repairing. Most evidential breath-alcohol instruments employing IR incorporate multiple wave lengths to increase specificity for ethanol (Fig. 1). Duringthe1980s, fuel-cell technology, which operates on the principle of electrochemistry, also emerged as a useful analytical method in forensic Tungsten filament IR beam breath-alcohol Breath in measurement.

Although fuel cells have been employed typically in screening devices, their technology has improved dramatically in recent years. Instruments employing both IR and fuel-cell method ologies to quantify ethanol in breath for evidential purposes include the Alcotest 7110 (Draeger Safety) and the Intoximeter (Intoximeters Inc., USA). The advantage of the combined IR and fuel-cell instruments is that two different methodologies are used for measurement, thereby maximising the chance of detecting the presence of volatile substances other than alcohol and minimising the possibility of a false result.

Figure 1 Schematic of an IR breath testing instrument. The instrument contains a series of filters whose function is to indicate whether other substances are present which might interfere with quantification of BrAc concentration. The instrument uses the ratios of the C₁H vibrational stretching modes of ethanol at 2873.56 cm1 and 2949.85 cm^-1 to check whether interfering substances are present.