Determination of Methanol in Aerosol Products Containing Propellant

According to the official analytical method of methanol in commercial aerosol products, the concentration of methanol in their propelled solution was limited to less than 5%. The propelled solution was sampled by propelling aerosol into a flask for the evacuation of the propellant only. There was the possibility of occurrence of errors due to flying nebulized methanol in the procedure of propelling, or due to the high volume of dissolving propellant in the propelled solution. In this paper, after making some test aerosol products, the possibility of occurrence of error was discussed. The recoveries of methanol in the test aerosol products containing the ratio of 5% methanol/ethanol solution and isobutane by weight of 5 : 5, 4 : 6, 3 : 7 were high yields ranging from 97.5 to 99.2%. But those of 2 : 8 and 1 : 9 were 94.4% and 80.3% respectively due to the flying nebulized methanol. The detective yield of methanol in the propelled solution from the test aerosol products in the ratio of 3 : 7, after weighing the propelled solution by pouring it into a volumetric flask, with the propellant kept inside, was only 67.3%. The problem of dissolving propellant was solved by freeing the propellant while swinging the propelled solution flask on a water bath (20°C) within a tiny zeolite and weighing the propelled solution using a 1 mm i. d. tip dropping pipet. As a result of this experiment, it is suggested that the determination of methanol by the official analytical method may not be achieved in an aerosol containing high percentage of propellant.