Which statement best describes the Beer-Lambert Law in the context of infrared breath analysis?

Which statement best describes the Beer-Lambert Law in the context of infrared breath analysis?

• A. Infrared signal increases as the amount of alcohol increases.
• B. Infrared signal decreases directly proportional to the amount of alcohol present in the sample.
• C. Infrared signal is unaffected by the alcohol concentration.
• D. Infrared signal increases with sample humidity.

Answer: (B)

Beer-Lambert Law ties how much light is absorbed to how much of a substance is present along the light path. In infrared breath analysis, alcohol absorbs IR light at specific wavelengths, so when breath contains more alcohol, more IR is absorbed and less light reaches the detector. That means the detected infrared signal drops in proportion to the amount of alcohol in the sample. The other ideas don’t fit: the signal increasing with more alcohol would contradict the absorption effect; the signal being unchanged ignores the absorption dependence; and humidity isn’t the primary factor described by this law in relation to alcohol concentration.

Beer-Lambert Law ties how much light is absorbed to how much of a substance is present along the light path. In infrared breath analysis, alcohol absorbs IR light at specific wavelengths, so when breath contains more alcohol, more IR is absorbed and less light reaches the detector. That means the detected infrared signal drops in proportion to the amount of alcohol in the sample. The other ideas don’t fit: the signal increasing with more alcohol would contradict the absorption effect; the signal being unchanged ignores the absorption dependence; and humidity isn’t the primary factor described by this law in relation to alcohol concentration.