<prompt> This instrument is based on the principle ofHenrys lawWidmarcks lawOsmosisNeutron activation analysis  <response>: This is based on Henrys law which states that when a volatile chemical ethanol is dissolved in a liquid blood and is brought to equilibrium with air alveolar breath, there is a fixed ratio between the concentration of the volatile compound ethanol in air alveolar breath and its concentration in the liquid blood, and the ratio is constant at a given temperature. Correlation between the breath and blood level, and the ratio is generally 2100 : 1. 