Determination of Ethanol in Breath
and Estimation of Blood Alcohol
Concentration with Alcolmeter S-D2
A.W. Jones and KÄ. Jönsson
Departments of Alcohol Toxicology and Internal Medicine, University
Hospital, 581 85 Linköping, Sweden.
1. Introduction
The technology of breath-alcohol analysis can be subdivided into two broad
categories; devices for pre-arrest screening of drunk drivers and more
sophisticated instruments for quantitative evidential purposes (1,2). The
Lion Alcolmeter S-D2 is a multipurpose hand-held device designed
originally for use as a roadside screening test. However, its easy-to-read
digital display and highly reproducible breath sampling system, has created
many applications for this instrument in alcohol research, industrial
chemistry, and clinical and emergency medicine. Although the Lion
Alcolmeter S-D2 has been available for many years, hardly any studies
have dealt with its precision and accuracy.
When breath-alcohol analyzers are used for legal purposes the results are
mostly reported as the concentration in the breath sample analyzed
(BrAC) expressed in units of mg/l, jig/lOO ml, or g/210 1. However, when
breath-alcohol analyzers are used in research and clinical medicine, the
BrAC is almost always translated into the presumed concentration in a
specimen of blood (BAC) having units of g/1, mg/dl, or g% w/v. To make
the conversion from BrAC into BAC, one assumes a constant blood:breath
ratio of alcohol (usually 2100:1 or 2300:1), which is used to calibrate the
instrument (3).
The precision and accuracy of Lion Alcolmeter S-D2 was evaluated in
experiments in-vitro with known strength air-alcohol standards and also invivo with volunteer subjects who ingested moderate amounts of alcohol.
2. Material and methods
2.1 Breath-alcohol instruments
Four examples of the Lion Alcolmeter S-D2 breath-alcohol analyzer were
provided by the manufacture (Lion Laboratories PLC, Barry, South
Alcohol, Drugs and Traffic Safety - T92
Ed. by Utzelmann / Berghaus I Kroj
Verlag TÜV Rheinland GmbH, Köln -1993
423
Glamorgan, Wales, UK). The Alcolmeter instruments were fitted with
digital scales marked in mg/1 breath and readings could be made to two
decimal places. After an initial control of the calibration, no further
adjustments were made throughout the experiments. A nother Alcolmeter
S-D2 instrument was available and this had a digital scale marked in terms
of mg/dl presumed blood-alcohol concentration based on a 2300:1
blood:breath ratio.
2.2 Experiments in vitro
Air-alcohol mixtures were generated using a wet-bath simulator device
manufactured by Guth Laboratories, Harrisburg, USA. The simulator
operates at 34°C and the air/water partition coefficient of ethanol at this
tem perature was taken from the literature, being 0.393 x 10'3 (4). The
concentration of ethanol in the equilibrated air-vapor emerging from the
simulator was calculated as the product of the concentration of ethanol and
the air/water partition coefficient. The simulator was charged with aqueous
ethanol standards prepared from absolute ethanol by first making a 10%
w/v stock solution and then volumetric dilution to give working standards
at concentrations of 50, 100, 175, 380 and 640 mg/dl. The exact
concentrations prepared were checked by headspace gas chromatography
and were within ± 2% of the target values and often much better than
this.
The Lion Alcolmeter S-D2 instruments were fitted with mouth-pieces
normally supplied. These tubes were joined to the outlet of the wet-bath
simulator using a 2 cm long plastic tubing. The operator blew through the
simulator to produce an equilibrated breath-sample at 34°C. When the airvapor standard had passed through the simulator for about 5 seconds, the
READ button of the Lion Alcolmeter S-D2 was pressed capturing a
sample for analysis. The 4 Alcolmeter S-D2 instruments were positioned
side-by-side and exposed 10 times to each of the air-alcohol vapor
mixtures. The same simulator charge was used for all 10 tests at each
concentration of ethanol. The time interval between making the replicate
tests varied from < 5 min to 15 min and was sometimes longer depending
on practical circumstances.
23 Experiments in-vivo
Ten male volunteers took part in these experiments. They drank a dose of
ethanol equivalent to 0.80 g ethanol per kg body weight in 30 minutes.
Ethanol was ingested in the morning, either after an overnight fast or after
the volunteers had eaten a standard breakfast. An indwelling catheter was
implanted in a cubital vein for taking blood samples at exactly 10, 20, 30,
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45, 60, 90, 120, 150, 180, 240, 300, 360, and 420 min after the start of
drinking. Blood was drawn into 5 ml Vacutainer tubes (Becton Dickinson,
USA) containing sodium fluoride (20 mg) and 75 units heparin. The
catheter tubing was flushed with heparin/saline between taking successive
samples. The concentration of ethanol in blood was determined in
duplicate by headspace gas chromatography as described in detail
elsewhere (5). The standard deviation (SD) of this m ethod was 0.6 mg/dl
at a mean BAC of 80 mg/dl.
3. Results
3.1 Precision and accuracy of analysis in-vitro
Table 1 summarizes the precision and accuracy of the Alcolmeter S-D2
when used to analyze air-alcohol vapor standards. The coefficients of
variation (CV), as one index of precision, were between 2% and 2.5% at
ethanol concentration up to 0.40 mg/1 and the mean response was within
± 0.02 mg/1 (± 1%) of the target values. When exposed to higher airvapor concentrations of alcohol, the CV was between 2% and 5% and
accuracy was within ± 6.6% of the target values. The consecutive tests at
5-10 min intervals tended to decrease as the number of tests increased at
concentrations of ethanol at 0.70 mg/1 and higher. The components of
variance between and within instruments depended in part on the
concentration of alcohol in the air-vapor samples analyzed. At 0.20 mg/1,
the SD between instruments was 0.0056 mg/1 and within instruments the
SD was 0.0028 mg/1. The pure analytical SD was 0.0037 mg/1.
Table 1. Precision and accuracy of Alcolmeter S-D2 when used to analyze
air-alcohol vapor standards produced from a breath simulator device.
BrAC Target
Value mg/1
Mean Response
mg/1 (N = 10)
SD
mg/1
CV%
Bias %
0.20 (46)1
0.201
0.005
2.5
+0.5
0.40 (92)1
0.404
0.009
2.2
+ 1.0
0.70 (161)1
0.677
0.014
2.1
-3.2
1.50 (343)1
1.40
0.049
3.5
-6.6
2.50 (575)1
2.34
0.117
5.0
-6.4
1 Approximate blood-alcohol concentration in mg/dl based on 2300:1 ratio.
425
3.2 Experiments in-vivo
Figure 1 gives two examples of blood and breath ethanol profiles for a
relatively fast and slow absorber of alcohol.
T im e , min
T im o , min
Fig. 1. Concentration-time profiles of ethanol in venous blood analyzed by
gas chromatography and values estimated using Lion Alcolmeter S-D2.
The mean difference between duplicate determinations with Alcolmeter SD2 (N = 109) was -0.11 ± 0.26 mg/dl (± SD) and this was not significantly
different from zero. The SD of the differences was 2.81 mg/dl and the 95%
range of individual differences was from -5.5 to +5.7 mg/dl. The precision
of a single determination is given by 2.81/21 being 1.98 mg/dl expressed in
terms of the coexisting BAC. The mean difference between venous BAC
and Alcolmeter S-D2 response (N = 109) was -0.37 ± 0.81 mg/dl (±SD )
426
and this was not significantly different from zero. The SD of the differences
and the 95% limits of agreement were 8.45 mg/dl and -17 to + 16 mg/dl
respectively. Figure 2 shows a blood/breath scatter plot of venous blood
alcohol (x-variate) and breath alcohol (y-variate) analyzed with Lion
Alcolmeter S-D2. The high correlation (r = 0.94), near zero intercept and
slope close to unity confirms the reliability of this device and the lack of
bias when used to estimate blood alcohol concentration.
120
100
“O
05
E 80
OJ
Q1
1
(/) 60
L_
<D
E
o
o
<
40
20
0
0
20
40
60
80
100
120
Venous Blood Alcohol, m g/d l
Fig. 2. Scatter plot of venous blood alcohol and estimated BAC according
to tests with Lion Alcolmeter S-D2. Note the near zero intercept and slope
close to unity.
3 3 Variability between instruments
Figure 3 compares the concentration-time profiles of ethanol in 2 subjects
tested in rapid succession with each of 4 Alcolmeter S-D2 instruments. The
SD of breath-alcohol measurements between instruments was 0.01 mg/dl
which corresponds to 2.3 mg/dl BAC equivalent.
4. Discussion
The uncertainty of any breath-alcohol test depends on analytical and
physiological sources of variation. Physiological variations such as the way
the subject exhales - pre-breathing maneuver - dominates the total
427
variability. Differences between instruments might depend on the care
taken in calibration procedure. The relative contribution of analytical and
biological sources of variation can be evaluated using analysis of variance
after making replicate measurements in each subject with several different
instruments.
T im e , h
T im # , h
Fig. 3. Concentration-time profiles of ethanol in breath for 2 subjects
tested with 4 different Alcolmeter S-D2 instruments.
The in-vitro experiments showed that at high concentrations of alcohol in
the breath (> 0.40 mg/1 or 92 mg/dl BAC) the Alcolmeter response tended
to decrease slightly as the number of tests made at short intervals (5 min)
increased. This observation has been reported elsewhere and is caused by
a "fatigue effect" of the electrochemical cell (6). Presumably, the products
of ethanol oxidation (acetaldehyde) requires time to diffuse away from the
electrode surface interfering with the oxidation of ethanol in each new test.
Experiments with human subjects showed that the Alcolmeter response
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was mostly higher than venous BAC during the absorption-distribution
phase of ethanol kinetics. In the post-absorptive phase the Alcolmeter
response was almost always less than the venous BAC (4). This observation
is not new and reflects the uneven distribution of alcohol in the vascular
system and arterio-venous difference existing after subjects ingested a bolus
dose of ethanol on an empty stomach. Breath-alcohol follows more closely
the arterial blood concentration and this exceeds the venous BAC until
equilibrium distribution of alcohol in all body fluids and tissue is complete.
Moreover, the magnitude and direction of these BAC-BrAC differences
depends also on the value of the blood/breath calibration factor used.
In conclusion, the precision and accuracy of Lion Alcolmeter S-D2 was
exceptionally good for a hand-held instrument with manual sampling
procedure. The training and experience of the person operating the unit
plays an important role in the precision of breath sampling. As expected,
accuracy and precision in-vitro was better than in tests with human
subjects. The stability of the calibration was remarkably good over long
periods and no adjustments were deemed necessary. The calibration of the
instruments should be checked periodically but making haphazard changes
is not recommended.
5. References
1.
Dubowski, KM. The technology of breath-alcohol analysis. US
D epartm ent of Health and Human Services, DHHS publication No
(ADM)92-1728, 1992, pp 1-38.
2.
Jones, AW. The measurement of alcohol in blood and breath for
legal purposes. In Human Metabolism of Alcohol, Vol. 1, edited by
K E . Crow and R.D. Batt, CRC Press, 1989, pp 71-99.
3.
Jones, AW. Blood and breath alcohol concentrations, Brit. Med. J.
305:955:1992.
4.
Jones, AW. Variability of blood:breath alcohol ratio in-vivo. J. Stud.
Ale. 1978;39:1931-1939.
5.
Jones AW, Schuberth, J. Computer-aided headspace gas
chromatography applied to blood-alcohol analysis: Importance of
on-line process control. J Forens Sei 1989;34:1116-1127.
6.
Jones AW. Evaluation of breath alcohol instruments: In-vitro
experiments with Alcolmeter pocket model. Forens Sei Int
1978;12:1-9.
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