breathalyzer and electronic alcohol breath analyzers faq

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breathalyzer and electronic alcohol breath analyzers

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Electronic Alcohol Breath Analyzers
Scientific Method and Technology
Specificity and Accuracy Expectations

breathalyzer and electronic alcohol breath analyzers

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 with the 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.

breathalyzer and electronic alcohol breath analyzers

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Because of this molecular exchange in the 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 with 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 milliliters (ml) of alveolar air will contain the same amount 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 ml of blood.

Electronic measuring devices have been developed to measure breath alcohol concentration using a fuel cell gas sensor that is specific to alcohol molecules. The fuel cell sensor has two platinum electrodes with 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, the end product is acetic acid, the main component in vinegar. The molecular structure of acetic acid is then expressed 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 atoms and the = 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 two electrons flow through a wire from the platinum electrode in the fuel cell sensor to an electrical-current meter and then to the platinum electrode on the other side of the cell. The two protons move through the lower portion 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 previously.


As stated above, the basic technology of these type devices is essentially similar. A gas specific microchip sensor is used to measure the amount of a specific target gas (or hydrocarbon) contained in a specific volume of air (exhaled breath) by determining the electrical charge produced by the chemical reaction converting ethanol 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.

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 methods; digital, analog, preset 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 the immediate 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 minimum 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 individually pre-calibrated during the 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 concentration 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 determined in the laboratory 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 time, 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 (example: 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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