ISO 1389-9:1977 pdf download.Phthalic anhydride for industrial use一Methods of test
1 SCOPE AND FIELD OF APPLICATION
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.
3 REAGENTS
During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity.
3.1 Sulphuric acid, ρ approximately 1 ,84 g/mI, about 96 % (m/m) solution or approximately 36 N.
5 PROCEDURE
Weigh, to the nearest 0,005g， about 5g of the test sample, add 100 mI of water and heat gently until the test portion is dissolved. Cool rapidly to room temper ature.(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±1 'C and add 25,0 mI of the potassium
permanganate solution (3.3). Mix thoroughly and leave to stand at 20±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.ISO 1389-9 pdf download.