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

Abstract

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.

Breath-alcohol analyzers and simulator solutions: a commentary on a deficient explanation of test results

“…The consequence of this argument can be exemplifi ed further by considering the following related scenario that has been described elsewhere by Labianca [3] and by Fitzgerald and Labianca [8] and which warrants brief mention here.…”

“…A simulator solution maintained at 34°C that generates a result of 0.10% on a properly functioning breathalcohol analyzer has an alcohol concentration of 0.1226% (0.1226 g/100 ml) and an estimated water-alcohol to airalcohol partition ratio (WAR) of 2573:1 [3,4]. Individuals with limited or no scientifi c training frequently explain the discrepancy between these two concentrations-that is, the breath-alcohol analyzer result of 0.10% and the actual simulator solution concentration of 0.1226%, respectively-by providing an explanation that is essentially defi cient and, therefore, confusing.…”

“…Consequently, the "breath-alcohol" analysis of the simulator solution generates a result lower than it should be, in accord with Eq. 3 [3]. …”

Deconvolving an estimate of breath measured blood alcohol concentration from biosensor collected transdermal ethanol data

“…The value of this constant depends on both the solvent and, more significantly, on temperature. The value that is typically used when the solvent is human blood and the solute is ethanol is 2100:1; blood will contain 2100 parts ethanol for each part ethanol measured in the breath at 34°C [15]. Because of the obvious legal ramifications for DUI prosecutions, the soundness of this model and what the appropriate value for the partition ratio should be are constantly coming under scrutiny.…”

Variables That Impact on the Results of Breath-Alcohol Tests

“…(4), that the BBR, which has units of "mL breath /mL blood " (2), is equal to k EtOH RT, where k EtOH is the Henry's law constant.…”