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I have seen all sorts of ways to detect alcohol using NIRS (Near InfraRed Spectrscopy) or FTIR, but they are all quite complicated in that they are using and analyzing a very wide spectrum. In addition, it is not clear as to the environment of where the alcohol is measured in. Some presentations are talking about measuring the OH-stretch of the RO-H in the region of 3200-3650 cm^-1.

Some related, but not very helpful questions are:

Is there a cheaper and more simple way to do this detection, using off-the-shelf components, like IR lasers or diodes?

  • I suppose "cheaper" would mean to use just one or very few frequencies, so that one doesn't have to analyze an entire spectrum.
  • What are these frequencies and how are they determined?

UPDATE:

Apparently the Blood Alcohol Concentration (BAC) is measured differently in different parts of the world. Just for reference:

0.1 g alcohol in 100 mL blood equals:

  • 0.1% (U.S., Canada, Australia)
  • 100 mg% (UK)
  • 1 ‰ = 1 permille grams alcohol per 1 liter blood (EU)
  • 22 mmol/L (in hospitals) millimols alcohol per liter blood.
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    $\begingroup$ You're looking at concentrations of alcohol of approximately 0.1%. It's going to be difficult do measure that easily in an IR spectrum. $\endgroup$
    – Zhe
    Apr 30 '19 at 19:19
  • $\begingroup$ @Zhe How did you get that number? $\endgroup$
    – not2qubit
    Apr 30 '19 at 23:33
  • $\begingroup$ Well, when you hit 0.5%, you're pretty close to dead if not dead, and 0.08% is the legal limit in US for driving. $\endgroup$
    – Zhe
    Apr 30 '19 at 23:42
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    $\begingroup$ The trouble with detecting alcohol (or glucose for that matter, which has been tried many times because of its utility for diabetics) in blood by IR is that blood is a very complicated mixture of things many of which also have features common to alcohol (like OH stretches). Extracting a specific signal from the noise requires vast computing power even if the signal is good enough (which is unlikely). $\endgroup$
    – matt_black
    May 1 '19 at 13:55
  • $\begingroup$ Interestingly, there are certain things that are significantly easier to measure. For example, a pulse oximeter reads blood O2 saturation really well, and it's just a red light that you clip to your finger. $\endgroup$
    – Zhe
    May 6 '19 at 20:10

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