Discussion

Analytical Performance

The analyzers exhibited reasonable performance at measuring vaporous ethanol reference standards in vitro, especially considering the low-cost of the devices. In the United States, the National Highway Traffic Safety Administration (NHTSA) offers performance recommendations for alcohol screening devices (ASDs) \cite{NationalHighwayTrafficSafetyAdministration2008}. For ASDs, the total allowable error at the 0.020 g/210L concentration is ± 60% at the 95% coverage interval. The analyzers examined in this study met this performance requirement, showing a total error of ≤ 15% at the 0.020 g/210L concentration, although they are not listed on the NHTSA's conforming products list of ASDs \cite{2012}
For in vivo use, manufacturers of the instruments should consider programing the instrument for a duplicate breath test sequence, reporting the mean of the two measurements, along with the associated uncertainty. An uncertainty function could be built into the software of the smartphone app to provide users with additional information about the uncertainty of the measurements obtained \cite{Gullberg_2011}. In addition, calibration reports could be recorded by the smartphone app and notify the user when recalibration is needed. In the final analysis, the performance requirements for breath alcohol analyzers is up to the end user’s tolerance for uncertainty.  

Potential Interfering Substances

Potential interfering substances are volatile organic substances other than ethanol on a person’s breath which have the potential to interfere with the accurate analysis of vaporous ethanol \cite{Gullberg1994,Jones1996,Jones1989,Jones2008a}. These substances have an impairing affect similar to or greater than that found with ethanol \cite{Caldwell1997-in,Cowan1990-xl}.  Normally, potential interfering substances are found in such low concentrations that they are unlikely to interfere with an ethanol breath test \cite{Flores1985a}. However, there are some circumstances in which interfering substances may be present in high enough concentrations that they may falsely elevate an ethanol breath test \cite{Caravati2010,Jones2007,Norfolk1997}.

Acetone

Acetone has been found in the breath of people with diabetes, during times of fasting, and in very low carbohydrate dieters \cite{Ruzsanyi2017}. Electrochemical fuel cell breath alcohol analyzers are known to be unaffected by acetone \cite{Falkensson1989}. The analyzers examined in this study use a fuel cell and did not respond to acetone.

Isopropanol

The analyzers showed an apparent ethanol response to isopropanol. Isopropanol may be present in elevated concentrations on a person’s breath after drinking denatured alcohol \cite{Jones1989a} or produced endogenously from the biotransformation of acetone to isopropanol \cite{Jones2015}. In one case study, a self-reported teetotaler obtained a false positive result on an electrochemical fuel cell breath alcohol analyzer after following a very low carbohydrate ketogenic diet \cite{Jones2007}. In another study, isopropanol in the breath was found to be elevated after eating a ketogenic meal \cite{Li2017}. Users engaged in very low carbohydrate ketogenic dieting should be aware of the possibility of obtaining elevated BrAC results based on their diet.

Methanol

Methanol may be present in elevated concentrations on a person’s breath after consuming large amounts of fruit \cite{Lindinger1997}, in alcoholics \cite{Wigmore2008,Jones1988}, or through accidental exposure due to the improper production of distilled spirits \cite{Kane1968,Paasma2007}. There are two unfortunate cases reported in the literature where a breath alcohol analyzer mistook methanol for ethanol, delaying medical treatment, resulting in the subjects dying from methanol poisoning \cite{Jones1989}. The analyzers examined responded to methanol. Users should be aware of the potential, but the unlikely possibility of elevated BrAC results due to methanol.

Limitations

Vaporous ethanol reference material produced by breath simulators cannot account for the complex physiologic gas exchange taking place in the lungs and airways of live subjects \cite{Jones1990,King2013,Gullberg1990,Anderson2003,Lubkin1996}, nor the heterogenous nature of breath alcohol produced during a single exhalation \cite{Vosk2014}. The SD of measurements from live subjects has been shown to be greater than the SD produced by breath simulators \cite{Gullberg1989}. Fuel cell breath alcohol analyzers need to be recalibrated periodically, and the longevity of the analyzers was not examined in this study. An important consideration for those wishing to use these instruments is that the instruments must be sent back to the manufacturer regularly for recalibration. Individuals or institutions using these instruments may need to keep several on hand while periodic recalibrations are performed. Regular users of these instruments should incorporate quality assurances practices to ensure the accuracy of the results meets the requirements of the intended use. Researchers should acknowledge the limitations of the instruments, as well as perform accuracy checks to ensure the analytical performance falls within the necessary limits required by the investigation \cite{Dubowski1994}.

Conclusion

The breath alcohol analyzers examined in this study showed reasonable ability to measure vaporous ethanol, especially at or below concentrations of 0.080 g/210L. At the 0.080 g/210L ethanol vapor concentration, the combined expanded measurement uncertainty was ≤ ± 0.013 g/210L at the 95% coverage interval for all instruments. The likelihood of false readings from potential interfering substances appears to be small but may be a concern for those engaged in ketogenic diets with elevated levels of isopropanol. The analyzers offer a rapid, cost-effective way to measure BrAC. Applications for potential use include drinking establishments, health care, family law, remote monitoring, personal use, research, and workplace testing. Finally, the accuracy and precision of personal breath alcohol analyzers must be evaluated against the intended use of the instrument.