Today we’ll look at another potential source of error with the Intoxilyzer – volatile chemical interference.   The Intoxilyzer 5000 uses a method of quantitative analysis called infrared spectroscopy to determine how much ethanol is present in the breath sample of a DWI suspect. Simply put . . . different molecules absorb infrared light at specific wavelengths. (actually the chemical bonds holding the atoms together in the molecule absorb the light) But, if one knows the absorption wavelength of the molecule you’re looking for, like ethanol, you can design a detector to identify how much radiant energy is absorbed in a sample. Then you can deduce by reliable scientific means (the Lambert-Beer Law) the number of absorbing molecules in the sample. But what if other molecules absorb energy at the same wavelengths? Won’t, then, the Intoxilyzer mistake those molecules for ethanol? Will this result in an overestimation of ethanol in a person’s breath?   The Intoxilyzer uses multiple wavelengths of infrared energy to look for ethanol. The Texas Breath Alcohol Testing Program Operator Manual admits that other substances absorb infrared energy at some of the same wavelengths as ethanol. Acetone, for instance. Acetone is a volatile organic chemical found in the body of those suffering from diabetes. Consequently, if an interfering chemical, like acetone, is in the breath of a DWI suspect the machine might register an overestimation.


The manufacturer of the Intoxilyzer has built in a detector to look for acetone. Fair enough. But what about other interfering chemicals the Intoxilyzer does not look for?   Chemicals like methanol and toluene also absorb at wavelengths similar to ethanol. Methanol is found in solvents and varnishes. Toluene is found in paints, thinners, and glues. If a person comes into contact with these interfering chemicals (through occupational exposure, for example) and takes a breath test, they run the risk of higher false test results. That is, the Intoxilyzer 5000 mistakes the interfering chemicals for ethanol.   Interestingly, the Intoxilyzer can be fitted with a sample capture device used to preserve a sample for re-analysis at a later date. This sample preservation device could be used to check for quality control and interfering chemicals present. However, in Texas this device is not currently utilized on the Intoxilyzer 5000. Another interesting fact? Texas has no standard procedure approved for use by their technical supervisors to verify the interfering chemical detection feature of the Intoxilyzer 5000 works properly and conforms to the manufacturer’s certification as advertised.  


Check out other articles of interest here. Also, visit my Bryan|College Station Criminal Defense Blog for other posts about DWI defense and trial advocacy.