A new system for automatic measurement of Permanganate Time

Abstract

Permanganate Time (PT) is a standard quality control test for oxidisable impurities in products such as ethanol, acetic acid, acetic anhydride, acetone, methanol, pyridine, propionic acid and tricresyl phosphate. The test relies on visual assessment of the change in pink colouration over a period of time of a sample of product to which has been added a standard solution of potassium permanganate. Typically, this time period is between 30 min and 2 h. The standard test, therefore, is very time-consuming as well as being highly susceptible to operator error and bias. An automated measurement system has been developed that employs a photodiode array spectrophotometer to monitor the colour of the mixture. Pre-processing of the spectrum eliminates any interference and provides accurate estimates of the PT, even in the presence of a heavy precipitate. The method by which the software determines the test result can be tailored by the user to suit particular products. Any number of such user configurations can be saved for future use.