Determination of methyl ester in atmosphere by the p-rosaniline method

Abstract

A sample of vapor of methyl ester is passed at a rate of 0.5 l/min through a midget impinger (with fritted glass beads attached to the tip of bubbler) containing 20ml of 0.5N sodium hydroxide solution. The solution is allowed to stand for 20 minutes or longer at room temperature until the ester is hydrolyzed to methanol.
The recommended analytical procedure is as follows. Acidify a 20 ml portion of the 0.5 M sodium hydroxide solution containing 20300μg of methyl ester by adding 2ml of 2.7M sulfuric acid. Swirl, add 1ml of 0.01g/ml potassium permanganate solution and 2ml of 0.3% (by volume) propionaldehyde solution. Swirl, keep the mixture at room temperature for 10 minutes. Reduce the excess oxidizing reagent by adding 1 ml of 0.02g/ml sodium sulfite solution. Swirl, add 2ml of p-rosaniline hydrochloride solution (dissolve 0.16g of the reagent completely in 24ml of conc. hydrochloric acid, and dilute to 100 ml) and 1ml of 2.7 M sulfuric acid. Swirl, and let stand for 30 minutes at room temperature. Measure the absorbance at 585 nm against the reagent blank obtained by the same procedure.