ASTM D1541 Test Method for Total Iodine Value of Drying Oils and Their Derivatives
8. Procedure
8.1 To a 250-mL glass-stoppered iodine flask (Note 2), add 5 mL of solvent. In this dissolve the specimen, weighed to 0.1 mg, using the weight of specimen prescribed in Table 1.
NOTE 6 - The specimen weight is so chosen as to result in a 200 to 250 % excess of reagent of the amount absorbed. After running the analysis, use the following calculation to determine whether the proper specimen size has been used:
E, % = [V1/(B - V)] x 100
where:
E= excess reagent,
V1 = Na2S2O3 solution required for titration of the specimen, mL, and
B = Na2S2O3 solution required for titration of the blank, mL.
If the reagent excess falls outside these limits, the analysis must be repeated using the proper specimen size.
8.2 Make sure that the specimen is completely dissolved, and then in a darkened room of light intensity preferably less than 0.5 footcandle (5.4 lx), as measured with a light meter, or in a darkroom under red safelight illumination, pipet into the flask 10.0 mL of the Hg(C2H3O2)2 solution. Swirl the flask two or three times, add 50.0 mL of the Rosenmund-Kuhnhenn reagent, and note the time. Stopper the flask, add a small amount of KI solution to the well of the flask to seal it, swirl until the contents are well mixed (2 or 3 s), and place the flask in a dark place at a temperature of 23 to 27°C.
8.3 Exactly 1 h after the addition of the Rosenmund-Kuhnhenn reagent to the specimen, bring the flask out into the arkened laboratory (or darkroom under red safelight), add 20.0 mL of KI solution by pipet, swirl two or three times, add 20 mL of water, swirl again, stopper the flask, and allow it to stand for 1 min. Then, using normal illumination, rinse the stopper and neck of the flask with about 10 mL of water.
8.4 Titrate the released iodine with Na2S2O3 solution by adding rapidly from the 50-mL buret, with continuous agitation, about 25 to 30 mL (all but 5 to 10 mL) of the required Na2S2O3 solution. Then, if low-actinic flasks are being used, transfer the contents to a colorless flask, rinsing three times with a total of about 30 mL of water, and complete the titration in the usual manner using starch indicator when near the end point. If clear flasks are used, there is no need to transfer. Simply add 30 mL of water and complete the titration as described, using starch indicator solution when near the end point.
8.5 With each group of samples, conduct at least two blank determinations following the same procedure as described in 8.1-8.4, except that no sample is added. In the titration, run into the flask about 40 to 45 mL of Na2S2O3 solution before completing the titration as described.
