Determination of ethanol in breath for legal purposes using a five-filter infrared analyzer: studies on response to volatile interfering substances

The analysis of ethanol in exhaled breath is widely accepted and used worldwide for legal purposes to gather evidence of alcohol-impaired driving. Most evidential breath-alcohol instruments incorporate infrared (IR) spectroscopy as the analytical principle focusing on C-H or C-O stretching frequencies in ethanol molecules. The instrument approved for legal purposes in Sweden is called Evidenzer and is equipped with five infrared filters of which four are used for identification and quantification of ethanol and the fifth is a reference filter. The response of Evidenzer was tested against 21 volatile organic compounds (VOCs), and the instrument was programmed to deduct any bias caused by these VOCs if present in a sample of breath. If the amount deducted exceeds a certain threshold value, the entire test is aborted. Whenever this happens, the police request a specimen of venous blood for analysis by gas chromatography. Of a total of 24 072 drunken drivers, the evidential breath-alcohol test was aborted on 27 occasions (0.11%) because an interfering substance was present above the critical threshold. The VOCs most commonly identified in blood were acetone, isopropanol and/or methyl ethyl ketone (MEK). Elevated levels of acetone and isopropanol might arise during ketogenesis in people suffering from diabetes, or in those who eat low carbohydrate diets. High concentrations of acetone and MEK are probably caused by people drinking a technical alcohol product (T-Red), which is available in Sweden and is denatured with these agents. This study confirms that relatively few apprehended drivers in Sweden have elevated concentrations of VOCs in breath other than ethanol. Even the aborted breath tests, to a large extent, contained ethanol above the legal limit for driving.