Discussion
Analytical Performance
The analyzers exhibited good performance at measuring vaporous ethanol in vitro, especially considering the low cost of the devices. At the 0.080 g/210L concentration, for example, both the C6 and the C8 showed levels of uncertainty similar to those found in more advanced breath alcohol analyzers used for evidential purposes \cite{Hwang_2016,Brockley_Drinkman_2019}. If the Pro model's calibration curve could have been adjusted it would have shown even smaller uncertainty the C6 and C8.
In the United States, the National Highway Traffic Safety Administration (NHTSA) promulgates performance recommendations for alcohol screening devices (ASDs) \cite{NationalHighwayTrafficSafetyAdministration2008}. The NHTSA's total allowable error for ASDs at the 0.020 g/210L ethanol vapor concentration is ± 0.012 g/210L at the 95% coverage interval. The analyzers examined in this study met this requirement, showing a total error of \(\le\) ± 0.003 g/210L at 0.020 g/210L concentration, although they are not listed on the NHTSA's ASDs conforming products list \cite{2012}.
For in vivo
use, manufacturers of these devices should consider programing the
instrument for a duplicate breath test sequence and report 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}. Also, calibration reports could be recorded by the smartphone app
and notify the user when recalibration is needed.
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,Logan_1994}. These substances have an impairing effect similar to or greater than 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}. The analyzers examined do not have an interfering substance detection mechanism such as those found in more advanced electrochemical analyzers \cite{Chan_2018}.
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,Jones_1992,Logan_1994} or produced endogenously from the biotransformation of
acetone to isopropanol \cite{Jones1995a}. 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
The analyzers examined responded to 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,Aghababaeian_2019}. 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}. Users should be
aware of the potential, but 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,Gullberg1990,Anderson2003,Lubkin1996,Wilson1986,Vosk2014}. The SD of measurements taken in vivo has been shown to be greater than the SD produced by breath
simulators \cite{Gullberg1989}. Further research is needed to determine the measurement uncertainty for in vivo results.
The calibration longevity of the
analyzers was not examined in this study. An important consideration for
those wishing to use these instruments is that the device 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.
Users of these instruments should incorporate quality assurance practices to
ensure the accuracy meets the requirements of the
intended use \cite{Dubowski1994}. The use of compressed ethanol-gas reference standards would be a convenient way to perform accuracy checks \cite{Dubowski1996-dw,Silverman1997-zs}. Further investigation with these analyzers using compressed ethanol-gas standards is needed, as the efficacy was not assessed in this study.
Conclusions
The breath alcohol analyzers
examined in this study showed the ability to measure vaporous
ethanol with confidence in the results, especially at concentrations \(\le\) 0.080 g/210L. At the
0.080 g/210L ethanol vapor concentration, the combined expanded
measurement uncertainty was \(\le\) ± 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. More work needs to be conducted with these instruments in vivo to determine the measurement uncertainty for the results which include a biological component.