Colorimetric method for determination of ethanol in presence of methanol

A method is described for the determination of ethanol in the presence of methanol without pre-separation. The sample is oxidized to give acetaldehyde and formaldehyde. 2-Thiobarbituric acid reagent is added and selectively forms a pink adduct with acetaldehyde, but not with formaldehyde. The method is sensitive, obeys Beer's law in the concentration range 18-80 microgram/mL, and has an advantage over other methods because it does not detect any "apparent normal value" of alcohol in blood.