INDUSTRIAL OILS AND DERIVATIVESAOCS Official Method Tg 1-64 Reapproved 2009 Iodine Value, Wijs Method DEFINITION The iodine value is a measure of the unsaturation of industrial oils and derivatives and is expressed in terms of the number of cg of iodine absorbed per g of test sample (% iodine absorbed). SCOPE Applicable to normal industrial oils and derivatives, such as natural or synthetic drying oils and their fatty acids. For a specific class or product, refer to the AOCS method for testing the particular product (see Notes, 1). Replaces Ka 9-51. APPARATUS 1. Glass-stoppered bottles or wide mouth Erlenmeyer flask—500 mL. 2. Glass-stoppered volumetric flask—conforming to National Institute of Standards & Technology (NIST) tolerances and accurately calibrated to contain 1000 mL. 3. Pipets—5, 20, and 25 mL. 4. Filter paper—Whatman no. 41H, or equivalent. REAGENTS (See Notes) 1. Glacial acetic—ACS grade. The permanganate test should be applied to be sure that this specification is met. (a) Permanganate test—dilute 2 mL of the acid with 10 mL of distilled water and add 0.1 mL of 0.2 M KMnO4. The pink color must not be entirely discharged within 2 hr. 2. Potassium iodide—ACS or AR grade. 3. Chlorine—99.8% (see Notes, Caution). Satisfactory commercial grades are available in cylinders, but gas must not be dried by passing through sulfuric acid (sp. gr. 1.84) before introducing into the iodine solution. Note—Prepared Wijs (see Notes, Caution and 2) solution is available commercially and may be used in place of laboratory-prepared solution. 4. Soluble starch—tested for sensitivity. Make a paste with 1 g of starch and a small amount of cold distilled water. Add, while stirring, 200 mL of boiling water. Place 5 mL of this solution in 100 mL of water and add 0.05 mL of 0.1 M iodine solution. The deep blue color produced must be discharged by 0.05 mL of 0.1 M sodium thiosulfate. 5. Potassium dichromate—ACS grade. The potassium dichromate is finely ground and dried to constant weight at about 110°C before using. Note—A standard sample of potassium dichromate with a certificate of analysis may be obtained from the National Institute of Standards Testing in Washington, D.C. This sample, or equivalent, is strongly recommended for the primary standard for this method. Treat as directed in the certificate of analysis accompanying the sample. 6. Sodium thiosulfate (Na2S2O3·5H2O)—ACS grade. 7. Iodine—ACS grade. 8. Carbon tetrachloride—ACS grade (see Notes, Caution, Recommendations and 5). 9. Wijs solution, AR grade (see Notes, Caution). SOLUTIONS 1. Potassium iodine solution—dissolve 150 g in distilled water and make up to 1 L. 2. Starch indicator solution—make a homogeneous paste of 10 g of potato starch in cold distilled water. Add to this 1 L of boiling distilled water, stir rapidly and cool. Salicylic acid (1.25 g/L) may be added to preserve the indicator. If long storage is required, the solution must be kept in a refrigerator at 4–10°C (40–50°F). Fresh indicator must be prepared when the end point of the titration from blue to colorless fails to be sharp. If stored under refrigeration, the starch solution should be stable for about 2–3 wk. 3. Sodium thiosulfate solution, 0.1 M—dissolve 24.9 g of sodium thiosulfate in distilled water and dilute to 1 L. (a) Standardization—weigh 0.16–0.22 g of finely ground and dried potassium dichromate into a 500 mL flask or bottle by difference from a weighing bottle. Dissolve in 25 mL of water, add 5 mL of hydrochloric acid, 20 mL of potassium iodine solution and rotate to mix. Allow to stand for 5 min and then add 100 mL of distilled water. Titrate with sodium thiosulfate solution, shaking continuously until yellow color has almost disappeared. Add 1–2 mL of starch indicator and continue the titration, adding the thiosulfate solution slowly until the blue color has just disappeared. The strength of the sodium thiosulfate solution is expressed in terms of its molarity. Molarity of Na2S2O3 solution = 20.394 × mass of K 2 Cr2 O7 , g volume, mL of sodium thiosulfate solution Page 1 of 4 0 g of iodine in 1 L glacial acetic acid. (3) Boil briskly for 10 min. Pass dry chlorine gas into the iodine solution until the original titration is not quite double.1 M sodium thiosulfate solution to a starch end point. Page 2 of 4 . 6. (b) Wijs Solution—Using a graduated cylinder pour 117. Remove the flasks from storage and add 20 mL of KI solution. Recommendations and 5).1 g of iodine monochloride to 1 L of glacial acetic acid and filter through Whatman no. Pipet the 25 mL of Wijs solution into flask containing the test sample. Weigh the test sample (see Notes. dry 500 mL Erlenmeyer flask. 6 and 7. The original solution and finished Wijs solution are both titrated with Na2S2O3 solution as directed in Procedure. Dissolve 13.1 M Na2S2O3 solution. A characteristic color change takes place in the Wijs solution when the desired amount of chlorine has been added. 41H filter paper or equivalent into a clean and dry actinic glass bottle.1 M sodium thiosulfate solution to a starch end point. 4). Add 1–2 mL of starch indicator solution and continue the titration until the blue color has just disappeared. and mix well. 5. Titrate with 0. mL. cool and add 30 mL of 2% sulfuric acid and 15 mL of 15% potassium iodide solution. 4. Note-All glassware must be absolutely clean and dry. Store the flasks in a dark place for 30 min at a temperature of 25 ± 5°C. The temperature during melting and filtering should not exceed the melting point of the test sample by more than 10°C. and filter through filter paper to remove any solid impurities and the last traces of moisture. (3) Pipet 20 mL of Wijs solution into the flask. Cool remove a small quantity (100–200 mL) and set aside in a cool place for future use. (2) Add 15 mL of 15% potassium iodine solution.1 mL of the stock solution into a standard 5 lb bottle of glacial acetic acid and mix well by shaking. of total halogen content as mL sodium thiosulfate PROCEDURE 1.10 ± 0. Prepare and conduct at least two blank determinations with each group of test samples simultaneously and similar in all respects to the test samples. (2) Pipet 5 mL of the Wijs solution into the flask containing the saturated chlorine water. oiticica or dehydrated castor oil. CALCULATIONS Halogen Ratio R = 2A 3B − 2A Where— A = volume of titrant. 2. Gentle heating may be necessary to promote solution. (4) Titrate with 0. followed by 100 mL of distilled water. Discard the solution if a precipitate forms on standing. A convenient procedure is to add a small excess of chlorine and immediately bring back to the desired titration by addition of some of the original iodine solution which was taken out at the beginning. For conjugated oils such as tung. Wijs solution (see Notes. adding it gradually and with constant and vigorous shaking (see Notes. Table 1 is a guide to the size of test sample to weight. if it is not already liquid. and swirl to ensure an intimate mixture. Filter rapidly to prevent contamination with moisture and store in a cool place. allow the absorption to proceed for 1 hr at 25 ± 1°C. stopper the flask. 5. Melt the test sample. 3) accurately into a 500 mL flask or bottle to which has been added 20 mL of carbon tetrachloride (see Notes.0 ± 0. 3. (b) Total halogen content— (1) Pour 150 mL of recently boiled distilled water into a clean.INDUSTRIAL OILS AND DERIVATIVES Tg 1-64 • Iodine Value. mL. 7. The weight of the test sample must be such that there will be an excess of Wijs solution of 100–150% over the amount absorbed. The procedure for determining the ratio is as follows: (a) Iodine content— (1) Pour 150 mL of saturated chlorine water into a 500 mL Erlenmeyer flask and add a few glass beads. Caution) or other solvent (see Notes. This may be used to assist in judging the end point. (4) Mix well. and titrate immediately with 0. The test sample must be absolutely dry. Caution) can be purchased (see Reagents) or prepared in the laboratory. Wijs Method 4. and heat to boiling. Continue the titration until the yellow color has almost disappeared.1. The I/Cl ratio of the Wijs solution shall be within the limits of 1. The Wijs solution may be prepared from commercial iodine monochloride as follows: (a) Stock Solution—Add 317 ± 0. Shake. of iodine content as mL sodium thiosulfate B = volume of titrant. These recommendations do not represent official approval by the AOCS Uniform Methods Committee. Wijs solution causes severe burns and vapors can cause lung and eye damage. Isooctane has been reported to be a suitable replacement for chloroform in the peroxide value method. A fume hood should be used at all times when using chlorine. the preparation and separation are performed as directed in AOCS Official Method Cd 6-38. Potassium dichromate is toxic by ingestion and inhalation. Page 3 of 4 . mL of blank S = volume of titrant. NUMBERED NOTES 1. 1. Mechanical stirring is satisfactory for agitating during the addition of thiosulfate. 5. It is a strong oxidizing agent and should not be allowed to come in contact with organic materials. weigh 0. moisture and light. and therefore could be tried as a substitute for carbon tetrachloride in the iodine value method. 4. g Where— B = volume of titrant.13 g. The TLV is 1 ppm in air. Chlorine is a poisonous gas. the TLV (350 ppm) is less than those of chloroform. See AOCS Methods Cd 1b-87 and Cd 1d-92. A fume hood should be used at all times when using carbon tetrachloride. It should not be used to extinguish fires. RECOMMENDATIONS Cyclohexane has been proposed as a replacement for carbon tetrachloride in the iodine value method—see AOCS Recommended Practice Cd 1-87 (89). In the case of dehydrated castor oils. When the iodine value is required on the fatty acids of natural and synthetic drying oils. All Wijs solutions are sensitive to temperature.INDUSTRIAL OILS AND DERIVATIVES Tg 1-64 • Iodine Value. mL of test portion M = molarity of Na2S2O3 solution NOTES Caution Carbon tetrachloride is a known carcinogen. powdered metals and reducing agents. in particular lung cancer.1-Trichloroethane (TCE) has been suggested as a replacement for chloroform in this method. AOCS Official Method Cd 1d-92 and JAOCS 65:745 (1988).11–0. but rather is an empirical value indicative of the amount of unsaturation present. Cyclohexane and cyclohexaneacetic acid may also be considered as alternate solvents. 3. Wijs solution without carbon tetrachloride is available commercially. The TLV is 5 ppm in air. It is a narcotic. It is toxic by ingestion. Store in a cool and dark place and never allow to come to a temperature above 25-30°C. Use of a fume hood is recommended. It is a strong oxidizing agent and a dangerous fire risk in contact with organic chemicals.1. the result is not a measure of total unsaturation. There is sufficient evidence in humans for the carcinogenicity of chromium [+6].69 mass of test portion. hydrogen. 2. When the iodine value is determined on materials having conjugated systems. and methylene chloride. Wijs Method CALCULATION Iodine Value = (B − S) × M × 12. carbon tetrachloride. Although TCE is a halogenated hydrocarbon. Reproducible results are obtained which afford a comparison of total unsaturation. It decomposes to phosgene gas at high temperature. Laboratories that use these solvents may report their findings to the AOCS Technical Director. inhalation and skin absorption. 3377–0. g Iodine Value < 3 3 5 10 20 40 60 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 Page 4 of 4 Normal oils 100–150% excess of reagent 10 –10 8.1954–0.1287–0.1443 Conjugated oils 115–135% excess of reagent 0.1494–0.2252–0.5865 0.2822–0.2109 0.6346–0.1846 0.1155–0.1764 0.2456–0.3002–0.2540–0.2702–0.2117–0.1547 0.3281 0.576 5.0770–6.1737 0.1693–0.7935 0.1868 0.1814–0.2442 0.1351–0.1984 0.2271 0.1554 0.1801–0.2078–0.1671 0.1501–0.1337–0.1589–0.2953 0.5288 0.3460 2.2684 0.2646 0.2116 0.1228–0.4613–10.1406 0.1930–0.1210–0.1640 0.1411–0.1587–0.1374 .1730 0.3175–0.3175 0.1422–0.2461 0.1969 0. Wijs Method Table 1 Test portion mass.5384–3.1587 0.8461–1.1689–0.1476 0.1270–0.3691 0.3969 0.2886 0.4321–0.2268 0.3528 0.INDUSTRIAL OILS AND DERIVATIVES Tg 1-64 • Iodine Value.2309–0.