With breath alcohol determination, the measurement of the alcohol content in the breath is called. After consumption of alcoholic drinks or food there is a gas exchange between the air and the ingested alcohol in the alveoli (alveoli ). The alcohol contained in the peripheral blood is taken from the inhaled fresh air and delivered by the exhaled air, which a measurement can be made, allowing the conclusions to the blood alcohol concentration.
- 3.1 semiconductor sensor
- 3.2 infrared sensor
- 3.3 Electrochemical sensor
Field of application
The main field of application of breath alcohol analysis are traffic controls in the road by the police. This can be used directly on site to a first control blood alcohol level commercially available instruments. Since the reported data are relatively imprecise, placing a blood sample at a confirmation of the initial suspicion in the following, in order to perform an accurate measurement of the blood alcohol level under controlled laboratory conditions.
Even in the medical field and private use are so-called " breathalyzer " used.
Basic research on the measurement of breath alcohol concentration were carried out in 1981 in the then Department of Social Medicine and Epidemiology of the Federal Health Office.
For use come on different measuring principles -based instruments. Since 1953, injection tubes were used, which changed color in the case of positive detection due to a chemical reaction, today electronic measuring devices are used which directly display a digital value per thousand.
In France, all vehicle drivers are required in principle, such a simple injection tubes ( or other device for measuring breath alcohol ) carry; the test tube must have the marking NF and be durable for at least one year. This rule also applies to foreign drivers who spend their holidays in France or are just passing through. Vehicles with fixed Alcolock are exempt from the requirement. Background of the scheme is the high number of traffic accidents under the influence of alcohol: alcohol abuse and driving is responsible for 31 percent of all road deaths in France. According to Decree of 28 February 2013, the non- carrying of the instrument is, however, not as originally intended punished with a toll warning.
The 1953 developed by Draeger injection tubes are based on how a chemical reaction is still available. The ethanol contained in the air reacts with the chemicals present in the tube, with which is monitored by a color change. Each tube contains a mixture of potassium dichromate and sulfuric acid in a non-reactive carrier, silica gel. Of the exhaled air is blown through the mixture of ethanol, the ethanol to ethanal (acetaldehyde ) is oxidized, and the orange-red to green potassium chromium (III ) - " sulfate " is reduced. The sulfuric acid is used as proton donor, since the reaction takes place in an acidic environment. Also binds the water formed, to prevent further reaction of acetaldehyde to acetic acid. The length of the discoloration of the bed of packing is a rough indication of the content of ethanol. By means of a printed line the exceeding of a limit value can be identified. The reaction proceeds as follows:
Each tube is used only once, the durchzublasende breathing air volume is predefined by the maximum volume of the inflatable bag at the output ( standardized).
As a further development of the " breath tube " hand-held instruments were introduced, which today often are at the police station in use. Here, the measurement is based not on a chemical reaction with the color change, but the change in the potential between two electrodes which is of the ethanol content dependent, as measured by an electrochemical method. The measurement error of commercially available devices is relatively small ( / - 5 %), and the devices are shareable. However, calibration of the system is necessary at regular intervals.
In the stationary measuring instruments a double measurement is made: both electrochemical way (as in the hand-held instruments ) as well as by physical means using infrared measurement. With this dual measurement specific measurement values are up to 0.54 mg / l in court since 1998 as conclusive when it only comes to misdemeanors, in crime a more accurate determination by blood test is still required. Prerequisite is the correct operation of systems, such as compliance with a minimum time between last alcohol intake and measurement.
A Alcolock is the technical connection of a device for breath alcohol analysis with an immobilizer. It will be installed in motor vehicles and is designed to prevent ignition interlock by means of a car driving under the influence of alcohol.
See → Main article: Alcolock
Fundamentals of measurement methods
The various types of automated instruments based on different measurement method for the determination of the alcohol content in the breath. The three most common methods used are based on semiconductor sensors, infrared spectroscopy and electrochemical measuring cells.
A semiconductor sensor exposed to the gaseous substance from the ambient air reacts with this change in the electrical conductivity of the gas sensitive sensor layer. As sensitive semiconductive metal oxide layer are often used. These typically include tin oxide, tungsten oxide, titanium dioxide and zinc oxide. Since these have a large band gap, they must be heated during operation to temperatures between 200 ° C and 600 ° C, so a good intrinsic conductivity begins. In this case, a reversible absorption of oxygen molecules on the surface of the sensor layer takes place. At these high temperatures, the absorbed oxygen molecules can escape from the conduction band of the electron detector, whereby a condition of reduced conductivity. Join now gases such as Ethanol with the surface of the sensor in contact, an oxidation takes place with consumption of the oxygen molecules. The electrons are returned to the conduction band and it turns again increased conductivity a. Alcohol Tester with semiconductor sensors measure not only ethanol, among other things, they also respond to:
- Acetone ( in people with diabetes),
- Ammonia ( in people with liver and metabolic diseases).
In this measurement method, the principle of infrared ( IR ) spectroscopy is used. A light source emits in the infrared light of different wavelengths. The light passes through two windows and an interference filter. The interference filter passes only a specific wavelength in the range of about 9.5 microns. A radiation detector measures the intensity of the incoming light and transmits the corresponding signal to the processing electronics. Located between the two windows, a gas (ethanol ), the gas absorbs this specific wavelength of light. Thus, the light intensity decreases at the detector and thus its electronic output signal. This decrease is more pronounced the longer the light path and the stronger the gas (ethanol concentrate) is concentrated.
An electrochemical sensor
The method of determination by means of breath electrochemical sensor operates on the principle of the fuel cell. In such a measuring system are a measuring electrode, a counter electrode, and a small amount of electrolyte. The electrolyte and the electrode material are chosen so that the substance to be analyzed (ethanol) is electrochemically oxidized at the catalyst layer of the measuring electrode. On the opposite side of ambient oxygen is extracted at the cathode. This produces an electrode current can be measured through a load resistor. Again, other substances may be incorrectly identified, such as:
- Carbon dioxide,
- Acetone ( in people with diabetes),
- Eucalyptol ( after eating sweets )
- Ammonia ( in people with liver and metabolic diseases ),
In all methods, the electrical signals are amplified and filtered disorders as good as it gets. The signals are processed by electronics and displays the result on a display. In the first method ( semiconductor ) sensor, a current is measured, which varies with the change in conductivity of the sensor. With increasing concentration of alcohol content, the conductivity is greater and therefore the A metering electricity. In the second method (infrared sensor ), the incoming light intensity is measured by a detector. Emits the light by a higher concentration of alcohol, the incoming light intensity becomes smaller, and thus the signal. In the last process ( electrochemical sensor ), a measurement of the current over time. Thus, all the electrical charge is determined, are formed during the electrochemical reaction. The higher the alcohol content in the air, the greater the load.