Electrochemical Infrared Detection Breath Ethanol Analysis

Measurement of ethanol in expired breath is an easy and noninvasive means for assessing ethanol. Small amounts of unmetabolized ethanol are expired with every breath, the amount of which is proportional to the whole blood ethanol concentration. The relationship between whole blood ethanol and ethanol in alveolar air is based on the underlying assumption that the ethanol present in 1 mL of whole blood will equilibrate with 2100 ml of alveolar air. Various factors can influence the exchange ratio of ethanol in blood with that in alveolar air. These factors include lung volume, body temperature, breath temperature, and hematocrit. Body size also plays a role with smaller individuals showing greater expired blood ethanol levels. In addition, the relative accuracy of breath ethanol decreases with increasing blood alcohol concentrations. Although the low false-positive rate of the breath ethanol test is acceptable for legal purposes, measurement of blood alcohol is more appropriate for clinical use in emergency settings, because breath tests can underestimate the degree of toxicity (28).

Instruments to measure the ethanol content in expired breath are usually based on electrochemical detection. Ethanol present in expired air is oxidized by a fuel cell resulting in the production of free electrons. The current generated by these free electrons is directly proportional to the amount of ethanol oxidized by the fuel cell. Infrared detection of breath ethanol is the most common method in use. The amount of infrared energy lost because of absorption by ethanol is proportional to ethanol concentration in breath. Up to five different wavelengths may be used, resulting in high specificity for ethanol (29).

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