ISO 1389-9:1977 pdf download – Phthalic anhydride for industrial use – Methods of test
This part of ISO 1389 specifies an iodometric method for the determination of impurities oxidizable in the cold by potassium permanganate in phthalic anhydride for industrial use. This method is not specific for maleic anhydride, for which the polarographic method given in part VII (see the annex) should be used. This document should be read in conjunction with part I (see the annex).
2 PRINCIPLE
Oxidation of unsaturated organic acids and anhydrides in a test portion with an excess of cold standard volumetric potassium permanganate solution in the presence of sulphuric acid, followed by iodometric determination of the permanganate remaining.
5 PROCEDURE
Weigh, to the nearest 0,005 g，about 5g of the test sample, add 100 ml of water and heat gently until the test portion is dissolved. Cool rapidly to room temperature. (Phthalic anhydride is completely soluble under these conditions when hot; a precipitate forms on cooling but this in no way interferes with the rest of the determination.) After cooling, add 3 ml of the sulphuric acid solution (3.1), cool again to 20土1 ‘C and add 25,0 ml of the potassium permanganate solution (3.3). Mix thoroughly and leave to stand at 20土1 °C for 5 min. Add 1 g of the potassium iodide (3.2) and titrate the liberated iodine with the sodium thiosulphate solution (3.4) from the burette (4.1) (the colour change is very sensitive and does not require the addition of starch as indicator, except with coloured solutions). Carry out a blank test at the same time as the determi- nation, following the same procedure but omitting the test portion.