An improved method for the spectrophotometric determination of methanol by addition of ethanol

Abstract

A sensitivity of spectrophotometric determination of methanol, as oxidized to formaldehyde with pottassium permanganate-sulfuric acid, was increased by adding an ethanol solution to sample solution. Based on this fact, the following procedure was proposed to the spectrophotometric determination of methanol with chromotropic acid. Add 0.1 ml of 1.5% ethanol, 0.1 ml of 0.25 M sulfuric acid, and 0.2 ml of 5% potassium permanganate solution to 1.0 ml of the test solution containing (115)μg of methanol. Swirl the mixture, and keep it at room temperature for 20 min. Add 0.3 ml of 20% sodium sulfite solution to reduce the excess of permanganate. Swirl the mixture and add slowly 4 ml of 75% sulfuric acid. Add 0.3 ml of 2% aqueous chromotropic acid solution. Heat the mixture in a boiling water bath for 10 min with occasional swirlings. Upon cooling to room temperature, measure the absorbance at 575 nm against the reagent blank. The sensitivity of this procedure was about five times more than that of no ethanol procedure.