Interfering Substances Identified in the Breath of Drinking Drivers with Intoxilyzer 5000S

The selectivity of analytical methods used to determine ethanol in body fluids has always been an important concern in connection with chemical testing for intoxication. Allegations of false high breath-alcohol readings obtained because of the presence of volatile organic compounds (VOCs) other than ethanol is a well-known defense argument in trials concerning driving under the influence of alcohol (DUI). However, not much information exists to substantiate this claim, especially when modern analytical technology such as multiple wavelength infrared breath-alcohol instruments is used for forensic purposes. Whenever breath tests were aborted because interfering substances were ostensibly detected during routine evidential breath-alcohol analysis in Sweden with the Intoxilyzer 5000S, a sample of venous blood was taken for analysis by headspace gas chromatography. Most of the aborted breath tests could be explained by abnormally high concentrations of acetone, isopropanol, or methyl ethyl ketone in the samples analyzed. These VOCs originate in blood and breath after DUI suspects consume denatured alcohol preparations containing these solvents. However, the intoxilyzer 5000S sometimes aborted the evidential breath test even though VOCs other than ethanol were not identified in the blood samples. The reason for these latter tests being aborted is hard to understand because the blood-breath ratios of ethanol were within the range expected (1900:1 to 2800:1) for a large number of other DUI suspects tested with Intoxilyzer 5000S under the same conditions when interfering substances were not detected.