A modified IR spectrometer serves as a breathalyser or the intoxilyzer. The principle used for the detection of the alcohol level in the human system relies on the underlying process by which alcohol is absorbed into the blood stream.
Absorption of Alcohol in the Blood Stream
Alcohol refers to a large variety of organic compounds containing the hydroxyl group. Ethanol is the type used for consumption by the humans. Ethanol is a typically small molecule which makes its absorption into the blood easier.
Alcohols are volatile compounds. Thus, after entering the warm human body, a small amount of alcohol is vaporised each time you breathe. These vapours of alcohol enter the alveoli in the lungs from where they are passed out of the body as you exhale. The amount of alcohol fumes in the air you breathe out is directly proportional to the quantity of alcohol you consumed.
IR Spectroscopy and Breathalyzer
Different organic compounds are characterised by the IR wavelength they absorb. This is also called the IR signature of that particular compound. The breathalysers employ modified IR spectrometers calibrated to detect and absorb the ethanol.
The breath tube is preheated to conform to Boyle’s law and to ensure that each sample is consistent and accurate.
On the exhalation, the air breathed out enters a sample chamber. The commonly used Lion Intoxilyzer 6000s manufactured by the Lion Labs immediately begins to sample the exhaled air. The device sampling rate is 37 times per second and it continues to do so till a stream of air is breathed upon it for three consecutive seconds. The three seconds reading is taken for it contains the deep lung air having the highest concentration of the alcohol.
An IR detector embedded behind the sample chamber studies the air sample. The exact amount of IR radiated by the device is known, and therefore, the absorbed amount of IR is calculated. The microgrammes of alcohol present in the 100 ml of breath is calculated and displayed.
The intoximeters cannot be fooled by blowing down the sides of the mouthpiece or by sticking your tongue on it. There is only one way to beat a breathalyser: Do not drink and Drive!