ISO 1389-9:1977 download free.Phthalic anhydride for industrial use — Methods of test — Part IX : Determination of impurities oxidizable in the cold by potassium permanganate — lodometric method.
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.
ISO 1389-9 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 pemianganate 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, p approximately 1,84 g/mI, about
96 % (rn/rn) solution or approximately 36 N.
3.2 Potassium Iodide (Kl).
3.3 Potassium permanganate, 0,1 N standard volumetric
solution.
3.4 Sodium thiosulphate, 0,1 N standard volumetric
solution.
4 APPARATUS
Ordinary laboratory apparatus and
4.1 Burette, of capacity 50 ml, graduated in 0,05 ml or smaller divisions.
5 PROCEDURE
Weigh, to the nearest 0,005 g, about 5 g 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 ± 1 °C and add 25,0 ml of the potassium permanganate solution (3.3). Mix thoroughly and leave to stand at 20 ± 1 °C for 5 mm. 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.
6 EXPRESSION OF RESULTS
The content of oxidizable matter, expressed as a percentage by mass of maleic anhydride (C4H203), is given by the formula
where
V0 is the volume, in millilitres, of the sodium thiosulphate solution (3.4) used In the blank test; V is the volume, in millilitres, of the sodium thiosulphate solution (3.4) used in the determination; m is the mass, in grams, of the test portion.
NOTE — If the concentration of the standard volumetric solutions used is not exactly as spof led in the list of reagents, an appropriate correction should be made.
ISO 1389/I — General.
ISO 1389/Il — Measurement of colour of molten material.
Iso 1389/Ill — Measurement of colour stability.
ISO 1389/tV — Measuroment of colour after treatment with sulphuric acid.
ISO 1389/V — Determination of free acidity — Potentiometric method,
ISO 1389/Vt — Determination of phthalic anhydride content — Titrimetric method.
ISO 1389/V II — Determination of maleic anhydride content — Polarographic method.
ISO 13891V1II — Determination of ash.
ISO 1389/tX — Determination of impurities oxidizable in the cold by potassium permanganate — lodometric method.
ISO 13891X — Determination of 1,4naphthaquinone content — Colorimeiric method.
ISO 1389/Xl — Determination of iron content — 2.2Bipyridyl photometric method.