The Defense Perspective
Intoxilyzer does not measure alcohol. It measures electricity. The amount of electricity is related to the intensity of a light at a certain wavelength. The intensity of light is related to the amount of alcohol in the sample.
Think of the way florescent ink glows under a black-light tube. Florescent colors like yellow/orange/pink glow bright even though they are illuminated by an invisible ultraviolet to purple light while non-florescent versions of the same colors appear drab. The florescent ink absorbs light in the ultraviolet wavelength and emits it in the visible wavelength.
The same principle applies to alcohol molecules. Alcohol absorbs light of one wavelength and then emits light on a different wavelength. The Intoxilyzer has a "light bulb" for one wavelength and a light detector for the other.
The "detector" uses a what is basically a little solar panel that is sensitive to light emitted from alcohol molecules. By measuring the amount of electricity generated by this little solar panel, the machine estimates the "brightness" of the light in the alcohol emission wavelength. The brighter the light, the more alcohol vapor molecules.
You are allowed to have some amount of alcohol in your breath, but amount for "intoxication" is based on a percentage. One problem is that in order to calculate the percentage you need to how many non-alcohol molecules were in the sample. The intoxilyzer makes no attempt to count the other molecules, it just uses an average number guess.
Thanks for commenting on this issue, Arnie. The intoxilyzer is measuring the amount of infrared light absorbed at particular wavelengths, supposedly distinct for the ethanol molecule. However, there are other molecules that absorb at the same wavelength, like acetone, methanol, and toluene. The intoxilyzer is supposed to detect the presence of acetone in the breath sample and kick out an "interference" alert. But the absorption of other interfering molecules is not measured. I'll be writing later about interfering molecules that the intoxilyzer mistakes for ethanol in the breath.
I believe the bonds between "functional sets" is key to identifying molecules by their light absorbtion patterns.
Here is an image that I just made to help explain: http://img242.imageshack.us/
img2...elativeslb3.gif
You'll note that the other molecules that you mention can confuse the intoxilyzer machine not only contain the same elements as ethanol, but also a similar patters between groups. I tried to illustrate what I mean by using black dots for the intra-group bonds between atoms within the group and blue dots showing the bonds linking one group to another.
The thing is, although there are a bunch of molecules with a structure similiar to ethanol, they are all either poisonous or metabolites of ethanol. Even ethanol is poison, just not so much. I guess what I'm really saying is that this is all just fodder for striking back against claims of a perfect intoxilyzer... to muddy the waters. The least offensive of these other chemicals to drink is vinegar and who wants to do that? Yuck! If a guy is drinking methanol he is gonna be lucky to live long enough to get a DWI conviction.
verb: Thanks for commenting. In my next post on the Intoxilyzer 5000 I'll be discussing chemical interference by other substances that absorb infrared at the same wavelengths as ethanol. With your help I'll be correctly stating that the "bonds" between elements causes the absorption. Thanks, also, for the illustration. If you don't mind I'll include it in my next post.
Commenting by HaloScan
