Improved method on the determination of methanol using chromotropic acid

Abstract

It is found out that an addition of not only potassium permanganate, phosphoric acid, but also propionaldehyde accelerates more oxidation of methanol to formaldehyde.
By using this fact the following procedure of the spectrophotometric determination of methanol is proposed.
Oxidize 1ml of the test solution containing 115 μg of methanol by adding 0.2 ml of 0.3 v/v% propionaldehyde solution, 0.4 ml of potassium permanganate solution which is prepared by dissolving 1.5 g of the salt in 30 ml of water and 7.5 ml of 85% phosphoric acid, and by diluting the mixture to 50 ml. Swirl the mixture, and keep it at the room temperature for 5 minutes. Reduce excess permanganate by adding 0.2 ml of 0.2 g/ml sodium sulfite solution. Swirl the mixture, and add 0.3 ml of 0.02 g/ml aqueous chromotropic acid solution. Slowly add 4 ml of 75 v/v% sulfuric acid. Heat the mixture at 8085 °C for 10 minutes with occasional swirling. After cooling to the room temperature, measure the absorbance at 575 nm against the reagent blank obtained by the same procedure.
The improved method has higher sensitivity in comparison with the common method, and the calibration curve follows Beer's law over the range of 115 μg/ ml of methanol.