How are breath alcohol levels measured with ir spectroscopy?
Breath testing theory
It is based on the measurement of alcohol contained in deep-lung or “alveolar” air. As blood flows into the lungs to exchange carbon dioxide for oxygen, a part of the alcohol flowing in the blood stream is also exchanged and exhaled. Henry’s Law gives the estimation basis for the amount of alcohol in the bloodstream by measuring the amount of alcohol in the exhaled breath.
How does ir spectroscopy work
Infrared spectroscopy detection relies on an in-depth electronic analysis of the scope of a beam of infrared radiation passing through a breath sample to find the Alcohol concentration by identifying molecules based on how they absorb light. Using this technique, Spectrometers are able to measure the amount of alcohol present in the breath and display the results.
A light source emits infrared radiation, which is introduced through a measuring chamber and is finally measured by a detector. As the gas is measured in the chamber, it absorbs a part of the radiation due to molecules, reducing the intensity of the optical signal. This allows to deduce the concentration of gas.
However, more than a single compound may absorb radiation at one or more similar wavelengths to ethyl alcohol, but the IR Spectroscopy technology combined to algorithms is able to identify these particular compounds thanks to their signature wavelengths, and not take them into account.
IR Spectroscopy has the benefit to differentiate between alcohol level in lungs and in upper tracks, including residual alcohol in the breath. When you drink a glass of alcohol, molecules are present in your mouth, trachea and esophagus. When you take a test in a alcohol breathalyzer based in semiconductor or fuel cell technology, it could appear as a positive result not representative of your real alcohol level concentration in your blood. By measuring the concentration over the time at a high frequency, IR spectroscopy helps to detect false positive results.
On the graph below, we can better understand how IR spectroscopy can differentiate between alcohol levels in the lungs and in the upper tracks. IR spectroscopy continuously analyses the optical signal and can determine when alcohol is present. The particular shape of a “normal” breath is considered as a “plateau”, therefore any other shape is not representative of correct measurement, including alcohol present in mouth .
Infrared technology in breath testing
Alcohol regulation is different in every European country. So, it became critical to develop a portable technology available to consumers and professionals, to determine the precise amount of alcohol present in any given breath sample.
For the European market, breath alcohol test devices for consumers are mostly based on fuel cells or semiconductor sensors with their intrinsic drawbacks as regard to precision, time of life and necessity to be calibrated and eventually replaced.
Olythe developed for consumer use the first miniature and compact infrared breathalyzer using the same technology commonly used by law enforcement to validate alcohol level concentration.
Breath alcohol test devices for consumers are regulated by the EN16280 standard for the European market. Breathalyzers in order to complain to this standard shall reach defined precision level (below 20pppm) and, for example, being able to operate continuously through 75 measured tests. For a compact device such as the OCIGO, this requires strong performances in measurement precision and energy management.
The accuracy of a NDIR system is mainly due to its path length as described in the Beer-Lambert law, so reducing the overall size the measuring unit from 200mm (evidential breath analyzers) to less than 50mm is a real challenge.
Furthermore, the miniaturization of a NDIR system brings several additional challenges on the measuring cell: low power and high-performance infrared components, precise and stable thermoregulation and robust signal processing.
Until now, the IR Spectroscopy technology and its precision and reliability have been out of reach for people outside out of Law Enforcement, but thanks to Olythe and its 6 years of dedicated R&D, OCIGO its electronic breathalyzer using IRS technology was born.
Olythe was able to miniaturize this complex technology to fit in your pocket while giving you the precision of the IR Spectroscopy at the fuel-cell technology price.