AU J.T. 10(2): 75-80 (Oct. 2006)
Breath Alcohol Testers - Prevents Road Accidents David Tin Win Faculty of Science and Technology, Assumption University Bangkok, Thailand
Abstract
Four types of Breath Alcohol devices: Semiconductor Models (Breathalyzer), Fuel Cell Models (alcosensors), Infrared (IR) Spectroscopy Models (intoxilyzers), and Gas Chromatography (GC) Models (intoximeters) are described. Their function and work are examined and their effectiveness and possibility of error in DWI and DUI evaluations is discussed. Keywords: Alcosensors, BAC, BrAC, DUI, DWI, intoximeters, intoxilyzers.
Introduction the corresponding BAC. In other words, BrAC is correlated with BAC. Continuous mixing of Absorption of alcohol into the blood inhaled and exhaled air occurs in the lungs. stream affects people by making them Exchange of chemicals and air occur in the air- intoxicated. Alcohol intoxication in drivers can sacs called alveoli, which are surrounded by a cause road accidents. When is the driver fine network of capillary blood vessels. This is drunk? When is the driver under the influence the path via which alcohol enters the blood of alcohol? Technically it is determined by the stream. driver's blood alcohol level called the ‘blood Various types of electronic devices with alcohol concentration’ (BAC), which indicates alcohol specific sensors, such as lead selenide the degree of intoxication. In most countries sensor (Hungler & Stevens 1997), can measure 0.08 grams of alcohol per 100 mL of blood BAC. They commonly consist of a mouth piece (BAC 0.08) is set as the legal limit beyond and a sample chamber. The four basic types of which the driver is considered to be legally instruments are described and their drunk. Any driver with BAC > 0.08 can be effectiveness is discussed. considered to be driving under the influence of alcohol (DUI) or driving while intoxicated (DWI) and should not be allowed to drive. The Breath Alcohol Testers Blood alcohol levels may be evaluated by using the Breathalyzer (DUI Attorney Lawyer Breath alcohol testing devices were first 2005; Craig Medical Distribution Inc. 2005). developed for use by police in the 1940s. The There are two ways of measuring BAC (1) Breathalyzer was invented by Dr. Robert invasively by drawing a blood sample, and (2) Borkenstein of the Indiana State Police in non-invasively via breath, salvia, or urine 1954. An older model of the breathalyzer is samples. The latter is used mainly by law shown in Fig. 1. (Breathalyzer.net 2005). Some enforcement officials, and the former is prefer to classify breathalyzers based on color generally performed by specialists at health change due to alcohol chemical reaction. care institutions. Breath testing being quick and inexpensive The Models is the most common non-invasive test. How does a person's breath reveal the There are four types of breathalyzers amount of alcohol consumed? When a person (Camping Survival 2005). blows air into a breathalyzer the breath alcohol 1. Semiconductor Models (breathalyzer) content (BrAC) is measured and converted into 2. Fuel Cell Models (alcosensors)
75 AU J.T. 10(2): 75-80 (Oct. 2006)
3. Infrared (IR) Spectroscopy Models state is 3+). The degree of this color change (intoxilyzers) (caused by the change in chromium oxidation 4. Gas Chromatography (GC) Models state from 7+ to 3+) is directly related to alcohol (intoximeter) amount in expired air. For alcohol determination in exhaled air, the reacted Semiconductor Models (Breathalyzer): mixture in the first vial is compared (using the These types of units have the main advantage photocell system) to the other vial containing of being relatively inexpensive. Many the un-reacted mixture. semiconductor models are available and their use has increased rapidly. Classification Fuel Cell Models (Alcosensors): Among involves three levels - Level I: Novelty Grade, handheld breathalyzers, fuel cell units are the Level II: Intermediate Grade, and Level top standard. People such as police officers, III: Professional Grade. Some examples are employers, and substance-abuse counselors use shown in Fig. 2. fuel cell units. The units are more specific towards Breathalyzer process is based on the alcohol detection and their accuracy is chemistry of alcohol (Craig Medical comparable to a professional semiconductor Distribution Inc. 2005). The –OH group made unit. Consequently there is less chance of false up of one atom each of oxygen and hydrogen is readings from interfering non-alcohol substances. an alcohol functional group. It is what makes The sensor consists of a porous acid- compounds have alcoholic properties. electrolyte material sandwiched between two Compounds that contain –OH in their molecule platinum electrodes. The platinum oxidizes are all classed as alcohols. The alcohol in alcohol molecules in exhaled air flowing past alcoholic beverages is ethyl alcohol (ethanol) one side of the fuel cell producing acetic acid, with this molecular structure CH3-CH2-OH, protons and electrons. which is often abbreviated as C H OH or Two free protons and two free electrons 2 5 are released from the ethanol molecule when it EtOH (where Et = C H ethyl group). 2 5 is oxidized to acetic acid. The two electrons The Breathalyzer consists of a breath flow through a wire connected to the platinum sampling system, two glass vials containing electrode of the sensor, into an electrical- two identical chemical mixtures (sulfuric acid, current meter and then to the platinum potassium dichromate, silver nitrate and water) electrode on the other side of the cell. and a photocell system hooked to a meter for The two protons move through the lower measuring the color change due to the chemical portion of the fuel cell and combine with reaction. oxygen and the above electrons, to form water. The breath sample is bubbled through The electrical current produced depends on the one vial, in which the chemical reaction, shown number of free electrons, which in turn in Fig. 7 occurs. depends on the amount of breath alcohol 1. Sulfuric acid absorbs the alcohol from oxidized. A microprocessor measures this the air. electrical current, computes the total BrAC and 2. Alcohol CH3-CH2-OH reacts with converts it to equivalent BAC. potassium dichromate KCr2O7 producing An example of a Professional Grade Fuel chromium (III) sulfate Cr2[SO4]3, potassium Cell unit is shown in Fig. 3. Some are designed as evidential testers and results can be used as sulfate K2SO4, acetic acid CH3COOH and evidence in a court of law. water H2O. 3. The silver nitrate AgNO3 is a catalyst Infrared (IR) Spectroscopy Models that accelerates the reaction. (Intoxilyzer): These units are extremely Color wise, the reddish-orange accurate and specific. They are often used as - dichromate ion Cr2O7 (where chromium evidential testers in police stations. An oxidation state is 7+) changes to green example of an IR model is shown in Fig. 4. chromium ion Cr3+(where chromium oxidation
76 AU J.T. 10(2): 75-80 (Oct. 2006)
It consists of a lamp that generates a BrAC and BAC Correlation broadband IR beam containing many wavelengths. The IR beam passes through Alcohol is instantly absorbed into the the sample chamber and a lens focuses it blood capillaries of body tissues and organs, onto a spinning filter wheel made of narrow- which are directly exposed. This rapid alcohol band filters that are specific for the alcohol absorption occurs in the mouth tissues, the wavelengths. The photocell detects the light esophagus, the stomach and the small intestine. passing through each filter and converts to It is not metabolized (broken up), the chemical an electrical pulse, which is relayed to the structure remains intact. Thus alcohol remains microprocessor that interprets the pulses and as a separate component of blood. As blood gives the BAC, based on the IR absorption. flows through the air sacs (alveoli) in the lung membranes, carbon dioxide molecules CO2 (g) Gas Chromatography Models are exchanged for oxygen molecules O (g). (Intoximeter): These are based on the 2 During this gas exchange alcohol, being highly chromatographic separation principle. volatile is released with the carbon dioxide Alcohol peak is detected and its intensity is molecules. Hence the amount of alcohol in determined (Gomley 2004). They are called expelled breath and the amount of blood intoximeters. alcohol is related.
This molecular exchange in the lung What Is the Function? tissues allows the correlation between blood
stream alcohol concentrations and the expelled The sole function is to monitor a person's breath. It can be established by measuring the breath and indicate the amount of alcohol that alcohol evaporation rate in solution. This rate is person has taken. It provides a quick rough then expressed as a constant ratio of blood quantitative measurement that allows setting of alcohol concentration (BAC) to breath alcohol a legal limit for drunkenness. In most countries concentration (BrAC). Equivalent BAC can blood alcohol legal limit is 0.08, which readily be estimated by calibration with a translates to 0.08 grams of alcohol per 100 mL standard BrAC. The breath alcohol to blood of blood. alcohol ratio is 2,100:1. Thus 2,100 mL of In order to obtain an accurate correlation alveolar air contains the same alcohol amount between blood and breath alcohol levels as 1 mL of blood. If 100 mL of blood contains (typically 2100:1), the alcohol tester must be 0.08 grams of alcohol the BAC is 0.08 (Craig able to capture a deep lung-air sample. A Medical Distribution Inc. 2005). person's vital capacity (volume of air that can be expelled without collapsing the lung) can Calibration range from 7L to 1L, depending on factors such as age, gender, physical condition, and During the final production and assembly disease status. If a digital readout is produced process electronic breath analyzers are by the breathalyzer only after taking a very individually pre-calibrated, using a laboratory long breath sample, then there is a risk that the simulator device flow meter such as GUTH34C person won't be able to provide a breath and standard alcohol solutions of specific sample. On the other hand, if the breathalyzer concentrations. requires just a minimum amount of air before Each new test procedure is preceded by a providing a digital readout, then the correlation microchip recycle and zero balancing, hence between BrAC and BAC will be poor, the re-calibration is not necessary under normal estimated BAC will appear to be lower than the use. Accuracies are determined by comparing true BAC (Craig Medical Distribution Inc. simultaneous measurements of BrAC by the 2005). electronic device and a gas mass spectrometry
BAC of a blood sample.
77 AU J.T. 10(2): 75-80 (Oct. 2006)
Many independent variables are present temperature and humidity. Therefore a margin at any instant of testing. Hence conclusions of error is always present. This need to be cannot be drawn, and correlations between considered and an allowable margin is successive tests cannot be made. Each test required. The unit must be kept in a secure, result is specific to the test conditions and the clean, dry place at room temperature. Regular sample analyzed; and is independent of other calibration check against standards is essential. test results. Accurate readings of blood alcohol levels Some of these test specific variables cannot be obtained until at least thirty minutes include volume of breath sample, presence and after the most recent alcoholic drink. If amount of other gases in the sample, measured earlier, the breath sampling is more concentration of alcohol molecules in the from the mouth rather than the lungs, and a mouth, presence and amount of other gases higher reading may result. Truly accurate BAC detected in the immediate environment and is only obtained from blood sample others. measurements. Therefore each test result can only be A worrying fact is the possibility of interpreted independently and exclusively of mistaken identification of all compounds that other test results. This produces a common contain CH3 - methyl groups as ethyl alcohol misconception and false assumption that the [Note ethyl alcohol contains a methyl group devices can be "tested" by repeated tests, or CH3CH2OH]. Examples of such compounds worse still by erroneously anticipating a value are shown in Table 1. Acetone CH COCH and for any given test. 3 3 acetaldehyde CH CHO both contain methyl 3 Discussion groups and can be found in the human breath. Out of the one hundred chemicals in the breath How Effective Are They? 70-80% contains methyl groups. Infrared breath machines will detect each of these as The effectiveness depends on the ethyl alcohol. accuracy of measured data. The desired The effect is additive and the more non- accuracy is dictated by the purpose for which alcohol methyl groups detected the higher will the device is to be used. Equipment for be the blood-alcohol reading. Thus all the non- personnel, commercial, or law requires alcoholic compounds in the breath will have a different accuracies. cumulative effect and a magnified error will Accuracy expectations are related to the result. Hence there is always a probability of a cost of models. Models at the high price range person being mistakenly charged with DWI or use high quality components and can provide DUI, especially diabetics who tend to have accurate test results. On the other hand, lower acetone breath (San Diego DUI 2002). cost models do not yield laboratory accuracy or Anyone who drives a car under the specificity. But they are more cost effective for influence of alcohol is a public menace. The certain cases like personnel detection. They seriousness of DWI (driving while intoxicated) produce qualitative dependable results for such has made law enforcement authorities resort to usage. For evidentiary purpose more accurate strict enforcement of DWI statutes (San Diego equipment that matches laboratory accuracy is DUI 2002). Many physical methods of breath- demanded. Choice of equipment thus depends alcohol analysis to evaluate suspected OUIA on the intended purpose. (operating under the influence of alcohol) But overall these devices are effective drivers are currently used. But the enough to detect dangerous drunk drivers and Breathalyzer, developed by Borkenstein and prevent accidents on the road. However there based on alcohol chemistry, remains the tester are chances of mistakes from instrument errors. of choice (Craig Medical Distribution Inc. The alcohol sensor is highly sensitive and 2005). It is an enforcement instrument that will not function correctly when wet or serves as a reliable, noninvasive tool of damaged. Its response can also be affected by forensic alcohol analysis.
78 AU J.T. 10(2): 75-80 (Oct. 2006)
Suggestions for Improvement References
¾ Make sensors more specific to alcohol and more accurate. Breathalyzer.net. 2005. The CA-5000 Coin ¾ Promote better understanding of device operated breathalyzer. reliability.
Acknowledgement
This paper is based on the General Chemistry Program CT 1101 Technical Report Writing Projects submitted by the following semester 2/2004 students: Tahmina Haque 4716802; Shayne Batist 4726833; Katesuda Sumanmas 473757; Lu Paw Doh 4725168; Mr. Li Ming 4715204; Mr. Thana Puenpipat 4715471;Mr. Panlop Chutiwongtanapat 4715878; Mr. Natchaphatr Lorvoralak 4717448 and Ms. Preechaya Leelaphatthanawong 4715381.
79 AU J.T. 10(2): 75-80 (Oct. 2006)
Fig. 5. Schematic Diagram of an Intoxilyzer.
Fig. 1. An Older Breathalyzer.
a) Novelty Grade. b) Professional Grade. Fig. 2. Semiconductor Models. Fig. 6. Fuel Cell Detectors.
Fig. 3. Professional Fuel Cell Model.
Fig. 7. Chemical Reactions in Breathalyzers.
Table 1. Compounds with CH3 – can be misread as ethanol (San Diego DUI 2002) • Isopropyl Alcohol • Ethyl chloride • Propane • Acetic Acid • Butane • Butadiene
• Propylene • Dimethylether Fig. 4. IR Model. • Methane • Dimethylamine • Ethane • Dimethylhydrazine
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