North Carolina Intox EC/IR II Practice Exam

Henry's Law describes how a volatile substance distributes itself between a liquid and a gas at equilibrium, so the amount in the gas phase reflects the concentration in the liquid under the observed conditions. In breath testing, calibrating and validating the analyzer relies on creating a humid, breath-like gas that establishes the same kind of gas-liquid equilibrium the human alveolar breath has. A wet gas breath simulator provides a moist gas sample with a known ethanol concentration by allowing ethanol to partition between a liquid (calibration solution) and the surrounding gas, mimicking real breath conditions. This lets the instrument apply the same partition behavior it would encounter in a true breath sample, ensuring accurate readings. The other options don’t reproduce the breath-like humidity and equilibrium required for this gas–liquid relationship: a dry gas canister yields dry reference gas, the infrared analyzer measures absorption rather than generating the test gas, and a blood sample is not part of the breath-sample calibration.