The Flawed Nature of the Calibration Factor in Breath-Alcohol Analysis.


Labianca, Dominick A.


Journal of Chemical Education








Breath-alcohol analyzers used by law enforcement agencies to evaluate suspected driving-while-intoxicated (DWI) drivers are routinely calibrated with standard, dilute aqueous solutions of ethanol known as simulator solutions. The analyzers are deemed accurate if they generate results within an established margin of error consistent with ethanol concentrations equivalent to the actual concentrations of the simulator solutions. The fundamental flaw of this protocol is that it ignores the fact that a simulator solution is an ideal Henry_s law system, whereas a human test subject is not. Since breath-alcohol analysis is an application of Henry_s law, the level of accuracy ascribed to simulator-based calibrations cannot be applied to analyses involving humans because they are affected by physiological variables that can significantly impact the results of such analyses. This article addresses the importance of these variables, including blood:breath ratio variability, body temperature, and breathing pattern. Moreover, the article notes that, when standard ethanol-in-nitrogen compressed gas mixtures are used instead of aqueous simulator solutions to calibrate breath-alcohol analyzers, the same limitations of accuracy apply. Finally, emphasis is placed on the nature of the ideal calibration standard, namely that it should mimic the system to be analyzed, which is clearly not the case with the calibration protocol employed in breath-alcohol analysis.