Which law describes the relationship between infrared signal and alcohol concentration in breath analysis?

Which law describes the relationship between infrared signal and alcohol concentration in breath analysis?

• A. Boyle's Law
• B. Charles' Law
• C. Avogadro's Law
• D. Beer-Lambert Law

Answer: (D)

Infrared breath analysis relies on how much infrared light ethanol absorbs. The relationship that lets us turn an absorption signal into a concentration is described by the Beer-Lambert Law. For a fixed path length and a given wavelength, absorbance is proportional to concentration (A = εlc). In practice, ε is a constant for ethanol at the chosen wavelength, and the instrument keeps the path length constant, so the measured absorbance directly reflects how much ethanol is present. This is why the Beer-Lambert Law is used to quantify alcohol concentration from the IR signal. The other laws describe gas behavior or molecular counting and don’t relate light absorption to concentration in this context.

Infrared breath analysis relies on how much infrared light ethanol absorbs. The relationship that lets us turn an absorption signal into a concentration is described by the Beer-Lambert Law. For a fixed path length and a given wavelength, absorbance is proportional to concentration (A = εlc). In practice, ε is a constant for ethanol at the chosen wavelength, and the instrument keeps the path length constant, so the measured absorbance directly reflects how much ethanol is present. This is why the Beer-Lambert Law is used to quantify alcohol concentration from the IR signal. The other laws describe gas behavior or molecular counting and don’t relate light absorption to concentration in this context.