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Quality Medical & Forensic

Diagnostics Since 1984 ...

May 8, 2012 

 

Electronic Alcohol Breath Analyzers (Breathalyzers) 

•  Scientific Method and Technology 

•  Specificity and Accuracy Expectations 

SCIENTIFIC METHOD AND TECHNOLOGY 

When consumed, alcohol is immediately absorbed into the blood capillary structure of each successive body 

tissue and organ it is directly exposed to. Alcohol's rapid rate of absorption begins in the soft tissues of the 

mouth, continues through the esophagus, into the stomach and finally, the small intestine. Alcohol is somewhat 

unique in that as it enters the blood stream, it 's chemical structure is not metabolized but remains unaltered and 

intact. Consequently, alcohol becomes a separate and definable component of blood flow. As blood flows into and 

through the alveoli (air sacs) in the membranes of the lungs, carbon dioxide molecules are exchanged for oxygen 

molecules. Because alcohol will readily evaporate from a solution and is highly volatile, alcohol molecules are 

released w ith t he carbon dioxide molecules during this gas exchange. Therefore the concentration of alcohol 

molecules in the alveolar air of expelled breath is related to the concentration of the alcohol in the blood. As the 

alcohol in the alveolar air is exhaled, it can be detected by a breath alcohol testing device.

Because of t his m olecular exchange in t he lung tissue, the correlation 

between alcohol concentrations in the blood stream and the expelled breath 

can be established by measuring the exchange rate, or evaporation rate of 

alcohol in solution. This rate is then expressed as a constant ratio of blood 

alcohol concentration (BAC) to breath alcohol concentration. Using this 

constant or fixed ratio wit h a measured breath alcohol content, equivalent 

blood alcohol content can readily be calculated. The ratio of breath alcohol to 

blood alcohol is 2,100:1. This means that by volume, 2,100 mill i l iters (ml) of 

alveolar air wil l contain the same am ount of alcohol as 1 ml of blood. If a 

person's BAC measures 0.08, it means that there are 0.08 grams of alcohol 

per 100 m l of blood.

Electronic m easuring devices have been developed to measure breath alcohol

concentration using a fu el cell gas sensor that is specific to alcohol 

molecules. The fuel cell sensor has t wo platinum electrodes wit h a porous 

acid-electrolyte material sandwiched between them. As exhaled air flows past 

one side of the fuel cell, the platinum oxidizes any alcohol molecules in the 

air to produce acetic acid, protons and electrons.

The formula for reactive oxidation of the alcohol (ethanol) molecule can be 

chemically stated. If hydrogen atoms are caused to be stripped by reaction 

from the right carbon of ethanol in the presence of oxygen, t he end product

is acetic acid, the m ain component in vinegar. The molecular structure of 

acetic acid is then expr essed as O = H3C - C - O - H where C is carbon, H is 

hydrogen, O is oxygen, the hyphen is a single chemical bond between the atom s and t he = symbol is a double

bond between the atoms. When ethanol is oxidized to acetic acid, two free protons and two free electrons are 

released from the ethanol molecule.

These tw o electrons flow th rough a wire fr om the platinum electrode in the fuel cell sensor to an electrical- 

current meter and then to the plat inum electrode on the other side of the cell. The two protons move through the lower port ion of the fuel cell and combine with oxygen and the electrons on the other side to form water.

The more alcohol from the breath sample that is oxidized, the greater is the number of free electrons that are 

produced resulting in the greater amount of the electrical current that is produced. A microprocessor measures 

this electrical current to extrapolate total breath alcohol content then calculates the equivalent BAC using the 

constant ratio discussed pr eviously.

SPECI FICI TY AND ACCURACY EXPECTATIONS 

As stated above, t he basic t echnology of these type devices is essentially similar. A gas specific microchip sensor

is used to m easure t he amount of a specific target gas (or hydrocarbon) contained in a specific volume of air 

(exhaled breath) by det ermining the electrical charge produced by the chem ical reaction converting eth anol to 

acetic acid. Model quality and cost are differentiated by the sensor technology employed, processor type,

internal circuit board, features, options and other structural components.

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A micro processor chip on the sensor calculates the percentage of the target gas contained in the amount of 

breath sample analyzed for that specific quantity of breath sample. This percentage (Breath Alcohol Content) is 

then converted into equivalent Blood Alcohol Content (BAC) using standardized logarithms and displayed using 

various met hods; digital, analog, pr eset LEDs, audible beeps etc.

In all cases, exposing the sensor to any type of smoke or oxygen ion generator will produce false positive test 

results and inaccurate readings. This includes residual smoke in the lungs of a smoker and ambient smoke that 

may be present in t he im mediate area. Do not use an alcohol breath analyzer near any type of ion generator 

including popular air cleaners and central hvac electronic filtration systems. Smokers must wait a minim um 8 -10 

minutes after smoking to use a breathalyzer to insure that all residual smoke is absent from the lungs.

Generally, electronic breath analyzers are in dividually pre -calibrated d uring t he final production and assembly process. Calibration is accomplished using a laboratory simulator device (e.g. GUTH34C ), flow meter and control 

sample sets of specific alcohol concentrat ion solutions. Once the sensor is preset and calibrated, re- calibration 

should not be necessary under normal use as each new test procedure is preceded by a microchip recycle and 

zero balancing. Accuracy rates are d etermined in t he laborator y by simultaneously obtaining a breath sample 

reading from the electronic device and a drawn blood sample. The device reading is then compared the gas mass 

spectrometry reading from the blood sample.

Scientifically, because there are many independent variables present at any given point in time when a test is 

given, no conclusions can be drawn, or correlations made between successive test procedures. Each test result is 

independent of other test results and is specific to the conditions present and the sample analyzed at the exact 

moment the test was given. Some of these test specific variables include volume of breath sample, presence and 

amount of other gases in the sample, concentration of alcohol molecules in the mouth, presence and amount of 

other gases detected in the immediate environment and others. Example: the amount of breath sample will 

probably vary each time a test is performed resulting in a different reading for each test because of the gas to 

total volume logarithm. Therefore, each test result can only be interpreted independently and exclusively of other 

test results and correlation between tests should not be attempted nor is intended with these type of devices.

This fact results in a common misconception and false assumption by users of these devices that they can "test 

the tester" by repeatedly blowing into the unit to see if test results are the same each t im e, or more erroneously 

assuming what the test results should be for any given test event.

Obviously, accuracy expectations must also be related to the purchase cost of a particular model breathalyzer.

Higher priced models use higher quality components and therefore can be expected to provide more accurate test 

results. Lower cost models are not intended to provide laboratory accuracy or specificity and are more qualitative 

and utilitarian in function providing dependable results within the scope for which they were intended to be used 

(exam ple: personal versus evidentiary).

In conclusion, users of electronic alcohol breath analysis devices should not expect accuracy rates equivalent to 

precisely controlled laboratory results using flow meter or gas mass spectrometry equipment. Unexpected 

readings are almost always the result of user error, failure to follow device instructions, contamination of the 

sample by smoke or other environmental variable, failure to provide a sufficient breath sample or contamination 

of the gas sensor through misuse, abuse or absence of recommended cleaning maintenance. Test results obtained under the many possible variables of field use are generally assumed to be approximate to actual and 

not correlated consecutively.

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