How Are Breath Alcohol Levels Measured with IR Spectroscopy?
Breath Testing Theory
The measurement of alcohol levels using infrared (IR) spectroscopy is based on the analysis of alcohol contained in deep-lung or “alveolar” air. As blood flows into the lungs to exchange carbon dioxide for oxygen, some of the alcohol in the bloodstream is also exchanged and exhaled. Henry’s Law provides the basis for estimating the amount of alcohol in the bloodstream by measuring the amount of alcohol in the exhaled breath.
How Does Infrared Spectroscopy Work?
Infrared spectroscopy detection relies on the electronic analysis of a beam of infrared radiation passing through a breath sample to determine the alcohol concentration by identifying molecules based on how they absorb light. A light source emits infrared radiation, which passes through a measuring chamber and is then measured by a detector. As the gas in the chamber absorbs part of the radiation, the intensity of the optical signal is reduced, allowing the concentration of alcohol to be deduced.
Although multiple compounds can absorb radiation at wavelengths similar to ethyl alcohol, IR spectroscopy technology combined with algorithms can identify specific compounds based on their unique absorption patterns and exclude them from the analysis.
Benefits of IR Spectroscopy
IR Spectroscopy can differentiate between alcohol levels in the lungs and the upper respiratory tract, including residual alcohol in the mouth, trachea, and esophagus. Traditional breathalyzers based on semiconductor or fuel cell technology can sometimes produce false positives due to residual alcohol. By measuring the concentration over time at high frequency, IR spectroscopy helps detect and eliminate false positive results.
Infrared Technology in Breath Testing
Alcohol regulations vary across European countries, making it essential to develop portable technology for consumers and professionals that can precisely measure alcohol levels in breath samples. Most consumer breath alcohol test devices in Europe use fuel cells or semiconductor sensors, which have drawbacks in terms of precision, lifespan, and the need for calibration and replacement.
Olythe developed the first miniature and compact infrared breathalyzer for consumer use, using the same technology as law enforcement to validate alcohol concentration levels. Breath alcohol test devices for consumers are regulated by the EN16280 standard in Europe, which specifies precision levels and operational requirements, such as the ability to perform 75 continuous tests with high measurement accuracy and efficient energy management.
The accuracy of a Non-Dispersive Infrared (NDIR) system depends on its path length as described by the Beer-Lambert law. Reducing the size of the measuring unit from 200mm (evidential breath analyzers) to less than 50mm presents significant challenges. Miniaturization requires low-power, high-performance infrared components, precise and stable thermoregulation, and robust signal processing.
Until recently, IR spectroscopy technology was primarily used by law enforcement due to its precision and reliability. However, after six years of dedicated research and development, Olythe introduced OCIGO, an electronic breathalyzer using IRS technology. This compact device offers the precision of IR spectroscopy at a price comparable to fuel-cell technology, making it accessible to consumers.