Breathalyzer
A breathalyzer or breathalyser, also called an alcohol meter, is a device for measuring breath alcohol content. It is commonly utilized by law enforcement officers whenever they initiate traffic stops. The name is a genericized trademark of the Breathalyzer brand name of instruments developed by inventor Robert Frank Borkenstein in the 1950s.
Origins
Research into the possibilities of using breath to test for alcohol in a person's body dates as far back as 1874, when Francis E. Anstie made the observation that small amounts of alcohol were excreted in breath.In 1927, Emil Bogen produced a paper on breath analysis. He collected air in a football bladder and then tested this air for traces of alcohol, discovering that the alcohol content of 2 litres of expired air was a little greater than that of 1 cc of urine. Also in 1927, a Chicago chemist, William Duncan McNally, invented a breathalyzer in which the breath moving through chemicals in water would change color. One suggested use for his invention was for housewives to test whether their husbands had been drinking. In December 1927, in a case in Marlborough, England, Dr. Gorsky, a police surgeon, asked a suspect to inflate a football bladder with his breath. Since the 2 liters of the man's breath contained 1.5 mg of ethanol, Gorsky testified before the court that the defendant was "50% drunk". The use of drunkenness as the standard, as opposed to BAC, perhaps invalidated the analysis, as tolerance to alcohol varies. However, the story illustrates the general principles of breath analysis.
In 1931 the first practical roadside breath-testing device was the drunkometer developed by Rolla Neil Harger of the Indiana University School of Medicine. The drunkometer collected a motorist's breath sample directly into a balloon inside the machine. The breath sample was then pumped through an acidified potassium permanganate solution. If there was alcohol in the breath sample, the solution changed color. The greater the color change, the more alcohol there was present in the breath. The drunkometer was manufactured and sold by Stephenson Corporation of Red Bank, New Jersey.
In 1954 Robert Frank Borkenstein was a captain with the Indiana State Police and later a professor at Indiana University Bloomington. His trademarked Breathalyzer used chemical oxidation and photometry to determine alcohol concentrations. The invention of the Breathalyzer provided law enforcement with a quick and portable test to determine an individual's intoxication level via breath analysis.
Subsequent breath analyzers have converted primarily to infrared spectroscopy. In 1967 in Britain, Bill Ducie and Tom Parry Jones developed and marketed the first electronic breathalyser. They established Lion Laboratories in Cardiff. Ducie was a chartered electrical engineer, and Parry Jones was a lecturer at UWIST. The Road Safety Act 1967 introduced the first legally enforceable maximum blood alcohol level for drivers in the UK, above which it became an offence to be in charge of a motor vehicle; and introduced the roadside breathalyser, made available to police forces across the country. In 1979, Lion Laboratories' version of the breathalyser, known as the Alcolyser and incorporating crystal-filled tubes that changed colour above a certain level of alcohol in the breath, was approved for police use. Lion Laboratories won the Queen's Award for Technological Achievement for the product in 1980, and it began to be marketed worldwide. The Alcolyser was superseded by the Lion Intoximeter 3000 in 1983, and later by the Lion Alcolmeter and Lion Intoxilyser. These later models used a fuel cell alcohol sensor rather than crystals, providing a more reliable kerbside test and removing the need for blood or urine samples to be taken at a police station. In 1991, Lion Laboratories was sold to the American company MPD, Inc.
Chemistry
There are a variety of mechanisms used in breathalyzers, for example oxidation with potassium permanganate, or infrared spectroscopy.For an electrochemical electrolyzer, when the user exhales into a breath analyzer, any ethanol present in their breath is oxidized to acetic acid at the anode:
at the cathode, atmospheric oxygen is reduced:
The overall reaction is the oxidation of ethanol to acetic acid and water.
The electric current produced by this reaction is measured by a computer, and displayed as an approximation of overall blood alcohol content by the Alcosensor.
Accuracy
Breath analyzers do not directly measure blood alcohol concentration, which requires the analysis of a blood sample. Instead, they measure the amount of alcohol in one's breath, BrAC, generally reported in milligrams of alcohol per liter of breathed air. The relationship between BrAC and BAC is complex, and is affected by many factors.Calibration
Calibration is the process of checking and adjusting the internal settings of a breath analyzer by comparing and adjusting its test results to a known alcohol standard. Breath analyzer sensors drift over time and require periodic calibration to ensure accuracy. Many handheld breath analyzers sold to consumers use a silicon oxide sensor to determine the alcohol concentration. These sensors are prone to contamination and interference from substances other than breath alcohol, and require recalibration or replacement every six months. Higher-end personal breath analyzers and professional-use breath alcohol testers use platinum fuel cell sensors. These too require recalibration but at less frequent intervals than semiconductor devices, usually once a year.There are two ways of calibrating a precision fuel cell breath analyzer, the wet-bath and the dry-gas methods. Each method requires specialized equipment and factory-trained technicians. It is not a procedure that can be conducted by untrained users or without the proper equipment.
- The dry-gas method utilizes a portable calibration standard which is a precise mixture of ethanol and inert nitrogen available in a pressurized canister. Initial equipment costs are less than alternative methods and the steps required are fewer. The equipment is also portable allowing calibrations to be done when and where required.
- The wet-bath method utilizes an ethanol/water standard in a precise specialized alcohol concentration, contained and delivered in specialized breath simulator equipment. The wet-bath method has a higher initial cost and is not intended to be portable. The standard must be fresh and replaced regularly. In addition, the assumed water-air partition ratio for aqueous ethanol must be taken into account along with its associated uncertainty.
Non-specific analysis
One major problem with older breath analyzers is non-specificity: the machines identify not only the ethyl alcohol found in alcoholic beverages but also other substances similar in molecular structure or reactivity, "interfering compounds".The oldest breath analyzer models pass breath through a solution of potassium dichromate, which oxidizes ethanol into acetic acid, changing color in the process. A monochromatic light beam is passed through this sample, and a detector records the change in intensity and, hence, the change in color, which is used to calculate the percent alcohol in the breath. However, since potassium dichromate is a strong oxidizer, numerous alcohol groups can be oxidized by it, producing false positives. This source of false positives is unlikely as very few other substances found in exhaled air are oxidizable.
Infrared-based breath analyzers project an infrared beam of radiation through the captured breath in the sample chamber and detect the absorbance of the compound as a function of the wavelength of the beam, producing an absorbance spectrum that can be used to identify the compound, as the absorbance is due to the harmonic vibration and stretching of specific bonds in the molecule at specific wavelengths. The characteristic bond of alcohols in infrared is the O-H bond, which gives a strong absorbance at a short wavelength. The more light is absorbed by compounds containing the alcohol group, the less reaches the detector on the other side—and the higher the reading. Other groups, most notably aromatic rings and carboxylic acids can give similar absorbance readings.
Some natural and volatile interfering compounds do exist, however. For example, the National Highway Traffic Safety Administration has found that dieters and diabetics may have acetone levels hundreds or even thousands of times higher than those in others. Acetone is one of the many substances that can be falsely identified as ethyl alcohol by some breath machines. However, fuel cell based systems are non-responsive to substances like acetone.
Substances in the environment can also lead to false BAC readings. For example, methyl tert-butyl ether, a common gasoline additive, has been alleged anecdotally to cause false positives in persons exposed to it. Tests have shown this to be true for older machines; however, newer machines detect this interference and compensate for it. Any number of other products found in the environment or workplace can also cause erroneous BAC results. These include compounds found in lacquer, paint remover, celluloid, gasoline, and cleaning fluids, especially ethers, alcohols, and other volatile compounds.
Pharmacokinetics
Absorption of alcohol continues for anywhere from 20 minutes to two-and-one-half hours after the last consumption, generally taking around 40–50 minutes. During the absorptive phase, the concentration of alcohol throughout the body changes unpredictably, as it is affected by gastrointestinal physiology such as irregular contraction patterns. After absorption, the concentrations in the body settle down and follow predictable patterns. During absorption, the BAC in arterial blood will generally be higher than in venous blood, but post-absorption, venous BAC will be higher than arterial BAC. This is especially clear with bolus dosing, chugging a single large drink. With additional doses of alcohol, the definitions of absorption and post-absorption are less clear. However, once absorption of the last drink has finished, the concentrations will follow standard post-absorption curves. It is also not always clear from a BAC graph when the absorption phase finishes - for example, the body can reach a sustained equilibrium BAC where absorption and elimination are proportional.Across all phases, BrAC correlates closely with arterial BAC. Arterial blood distributes oxygen throughout the body. Breath alcohol is a representation of the equilibrium of alcohol concentration as the blood gases pass from the arterial blood into the lungs to be expired in the breath. The ratio of ABAC:BrAC is 2294 ± 56 across all phases and 2251 ± 46 in the post-absorption phase. For example, a breathalyzer measurement of 0.10 mg/L of breath alcohol characterises approximately 0.0001×2251 g/L, or 0.2251 g/L of arterial blood alcohol concentration.
The ratio of venous blood alcohol content to breath alcohol content may vary significantly, from 1300:1 to 3100:1. Assuming a blood-alcohol concentration of 0.07%, for example, a person could have a partition ratio of 1500:1 and a breath test reading of 0.10 g/2100 mL, over the legal limit in some jurisdictions. However, low partition ratios are generally observed during the absorption phase. Post-absorption, the ratio is relatively fixed, 2382 ± 119 , although this ratio was measured in a laboratory environment and variation may be larger in real-world scenarios.
Other false positives of high BrAC and also blood reading are related to patients with proteinuria and hematuria, due to kidney metabolization and failure. The metabolization rate of related patients with kidney damage is abnormal in relation to percent in alcohol in the breath. However, since potassium dichromate is a strong oxidizer, numerous alcohol groups can be oxidized by kidney and blood filtration, producing false positives.