1、Designation: D5768 02 (Reapproved 2010)Standard Test Method forDetermination of Iodine Value of Tall Oil Fatty Acids1This standard is issued under the fixed designation D5768; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the Wijs procedure for deter-mination of unsaturation (iodine value) of tall oil fatty ac
3、ids.1.2 Iodine value is a measure of the unsaturation of oils andfatty acids and is expressed in terms of the number ofcentigrams of iodine per gram of sample (weight percent ofabsorbed iodine).1.3 When this test method is used to determine the iodinevalue of fatty acids having conjugated systems, t
4、he result is nota measure of total unsaturated, but rather is an empirical valuethat affords a comparison of unsaturation. Total unsaturation ofconjugated systems may be measured in accordance with TestMethod D1541.1.4 The test method described here is not reliable for tall oilfatty acids containing
5、 an appreciable quantity of rosin.1.5 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user
6、 of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1541 Test Method for Total Iodine Value of Drying Oilsand Their Derivatives
7、3D1959 Test Method for Iodine Value of Drying Oils andFatty Acids3E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Significance and Use3.1 The iodine value of a fatty acid produ
8、ct is a measure ofthe unsaturated fatty acid content of that product and conse-quently a measure of the ease of oxidation or drying capacityof that fatty acid product.3.2 This test method measures the unsaturation as iodinevalue by addition of an iodine/chlorine reagent. The amount ofreagent absorbe
9、d is determined by back titrating the excessreagent and comparing it to a blank determination.3.3 In samples containing conjugated double bonds, theiodine value obtained is empirical since the reagent does notreact stoichiometrically with conjugated unsaturation. Whereno conjugation is present, the
10、iodine value obtained is ameasure of the total unsaturation. By using proper specimenweights, the empirical values obtained are useful for compara-tive purposes.3.4 This test method was developed in order to replace thehazardous solvent, carbon tetrachloride, used in Test MethodD1959 with the less h
11、azardous and more available solvents,iso-octane and cyclohexane. As data on the satisfactory use ofother solvents becomes available, this test method will beamended to include those solvents.3.5 This test method should have applicability to fatty acidsand oils other than tall oil fatty acid but that
12、 possibility has notbeen investigated.4. Apparatus4.1 BottlesGlass-stoppered bottles or Erlenmeyer flasksof 250-mL capacity.4.2 Pipets20 and 25-mL capacity.4.3 Analytical balance5. Reagents5.1 Purity of ReagentsReagent grade chemicals shall beused in all tests unless otherwise specified. Unless othe
13、rwiseindicated, it is intended that all reagents shall conform to theSpecifications of the Committee on Analytical Reagents of the1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommitte
14、e D01.34 on Pine Chemicals and Hydrocarbon Resins.Current edition approved June 1, 2010. Published June 2010. Originallyapproved in 1995. Last previous edition approved in 2006 as D5768 - 02 (2006).DOI: 10.1520/D5768-02R10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orconta
15、ct ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Har
16、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.American Chemical Society, where such specifications areavailable.4Other grades may be used provided it is firstascertained that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the d
17、etermi-nation.5.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Type I of Specification D1193.5.3 Acetic Acid (Glacial) 17.4 MVerify the absence ofsubstances reducing permanganate as follows: Dilute 2 mL ofthe acid with 10 mL of
18、water and add 0.1 mL of 0.1 Npotassium permanganate (KMnO4) solution. The pink colorshould not be entirely discharged at the end of 2 h.55.4 Iso-octane or cyclohexane.5.5 Chlorine (99.8 % Cl)(Warning: Extremely hazard-ous. For specific hazard information and guidance, see suppli-ers Material Safety
19、Data sheets.) Commercial grades ofchlorine available in cylinders may be used, provided the gas isdried by passing through concentrated sulfuric acid (H2SO4,spgr 1.84) before passing it into the iodine solution.Alternatively,the chlorine may be prepared by allowing concentrated hydro-chloric acid (H
20、Cl, sp gr 1.19) to drop onto potassium perman-ganate (KMnO4) or onto a mixture of KMnO4and manganesedioxide (MnO2). Dry the gas thus generated by passing itthrough concentrated H2SO4.5.6 Potassium Iodide Solution (150 g/L)Dissolve 150 g ofpotassium iodide (KI) in water and dilute to 1 L.5.7 Sodium T
21、hiosulfate, Standard Solution (0.1 N)Dissolve 24.8 g of sodium thiosulfate (Na2S2O35H2O) inwater and dilute to 1 L. Standardize against potassium dichro-mate (K2Cr2O7)6as follows: Weigh to 0.1 mg, by differencefrom a weighing bottle, 0.16 to 0.22 g of K2Cr2O7that has beenfinely ground and then dried
22、 to constant weight at 105 to 110Cprior to use. Place the K2Cr2O7in a 500-mL flask or bottle anddissolve in 25 mL of water. Add 5 mL of concentratedhydrochloric acid (11.6 M) and 20 mL of KI solution, androtate to mix. Allow to stand for 5 min and then add 100 mLof water. Titrate with the Na2S2O3sol
23、ution, while shakingconstantly, until the yellow color has almost disappeared. Add1 to 2 mL of starch indicator solution and continue the titration,adding the Na2S2O3solution slowly until the blue color has justdisappeared. Calculate the normality, N, of the Na2S2O3asfollows:N 5 A 3 20.39! / C (1)wh
24、ere:A =K2Cr2O7used, g, andC =Na2S2O3solution required for titration of theK2Cr2O7, mL.5.8 Starch Indicator Solution:5.8.1 Use soluble starch that will pass the following test forsensitivity: Make a paste with1gofstarch and a small amountof cold water. Add, while stirring, 200 mL of boiling water.Dil
25、ute 5 mL of this solution with 100 mL of water and add 0.05mL of 0.1 N iodine solution. The deep blue color producedmust be discharged by 0.05 mL of 0.1 N Na2S2O3solution.5.8.2 Make a homogeneous paste of 10 g of soluble starchin cold water. Add to this 1 L of boiling water. Stir rapidly andcool. Sa
26、licylic acid (1.25 g/L) may be added to preserve theindicator. If long storage is required, keep the solution in arefrigerator at 4 to 10C (40 to 50F). Prepare fresh indicatorwhen the end point of the titration from blue to colorless failsto be sharp.5.9 Wijs Solution(Warning: Extremely hazardous. F
27、orspecific hazard information and guidance, see suppliers Ma-terial Safety Data sheets.) Dissolve 13.0 g of iodine in 1 L ofacetic acid. Gentle heat may be necessary to promote solution.Cool and remove a small quantity (100 to 200 mL) and setaside in a cool place for future use. Pass dry chlorine ga
28、s intothe iodine solution until the original titration is not quitedoubled. A characteristic color change takes place in the Wijssolution when the desired amount of chlorine has been added;this may be used to assist in judging the end point. Aconvenient procedure is to add a small excess of chlorine
29、 andbring back to the desired titration by addition of some of theoriginal iodine solution that was taken out at the beginning.Determine the strength of the original iodine solution and thefinished Wijs solution by titration against 0.1 N Na2S2O3solution as directed in 6.4.NOTE 1Iodine monochloride
30、(Wijs solution) can be purchased com-mercially from various laboratory supply houses. The halogen ratio shouldbe checked prior to use.The halogen ratio, that is, the ratio of iodine to chlorine, can bedetermined by the Graupner-Aluise method.76. Procedure6.1 Melt the sample if it is not already liqu
31、id (do not exceed10 to 15C above the melting point of the sample) and filter, ifnecessary, to remove foreign materials.6.1.1 All glassware used in this test must be completelyclean and dry.6.2 Place into a 250-mL flask or bottle an amount of thesample such that there will be an excess of Wijs soluti
32、on of 1256 10 % for conjugated fatty acids and 125 6 25 % for normal4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemic
33、als, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.5“Analytical Reagents,ACS Specifications,”American Chemical Society, Wash-ington, DC, 1960.6National Institute of Standards and Technology Standard R
34、eference MaterialNo. 136 of potassium dichromate is recommended for this purpose and should betreated as directed in the certificate of analysis accompanying the standard sample.Available from NIST, Gaithersburg, MD.7Graupner, A. J., and Aluise, V. A., “A New Rapid Titration Method forDetermining th
35、e Halogen Ratio of Wijs Solution and of Iodine Monochloride,”Journal, American Oil Chemists Soc., February 1966 , p. 81.D5768 02 (2010)2or nonconjugated fatty acids. Specimen weights meeting thisrequirement are shown in Table 1. Add 20 mL of iso-octaneand swirl to dissolve.6.3 Pipet 25 mL of Wijs so
36、lution into the flask containingthe specimen and also into each of at least two additional flasksto be carried through as blanks. Stopper the flasks and swirl theflask containing the specimen to ensure an intimate mixture.Store the flask in a dark place for1hatatemperature of 25 65C.6.4 Remove the f
37、lasks from storage and add 20 mL of KIsolution and 100 mL of water. Titrate with Na2S2O3solution,adding it gradually and with constant and vigorous shaking(see Note 2). Continue the titration until the yellow color hasalmost disappeared. Add 1 to 2 mL of starch indicator solutionand continue the tit
38、ration until the blue color has just disap-peared.NOTE 2Mechanical stirring is satisfactory for agitating during theaddition of the Na2S2O3solution.7. Calculation7.1 Calculate the iodine value, I, as follows:I 5 B 2 V!N 3 12.69 / S (2)where:V =Na2S2O3solution required for titration of the speci-men,
39、 mL,B =Na2S2O3solution required for titration of the blank,mL,N = normality of the Na2S2O3solution, andS = sample used, g.8. Precision and Bias88.1 Interlaboratory Test ProgramAn interlaboratory studyof the iodine value of two tall oil fatty acids using two differentsolvents, was run in 2000. One of
40、 these substances had aniodine value of about 130 and the other an iodine value ofabout 82. The two solvents were cyclohexane and iso-octane.Each of 11 laboratories tested each of those materials in thetwo solvents. The design of the experiment, similar to that ofPractice E691 and a within and betwe
41、en analysis of the data aregiven in Research Report RR:D01-1127.8.2 Test Result using cyclohexaneThe precision informa-tion given below for the iodine value is for the comparison oftwo test results each of which is the average of three testdeterminations as follows:8.2.1 Repeatability limit, 95 % (w
42、ithin laboratory) = 1.0.8.2.2 Reproducibility limit, 95 % (between laboratories) =7.0.8.2.3 These terms (repeatability limit and reproducibilitylimit) are used as specified in Practice E177. The respectivestandard deviations among test results, related to the abovenumbers by the factor of 2.8 are as
43、 follows:8.2.4 Repeatability standard deviation = 0.4.8.2.5 Reproducibility standard deviation = 2.5.8.3 Test Result using iso-octaneThe precision informa-tion given below for the iodine value is for the comparison oftwo test results each of which is the average of three testdeterminations as follow
44、s:8.3.1 Repeatability limit, 95 % (within laboratory) = 2.3.8.3.2 Reproducibility limit, 95 % (between laboratories) =6.9.8.3.3 These terms (repeatability limit and reproducibilitylimit) are used as specified in Practice E177. The respectivestandard deviations among test results, related to the abov
45、enumbers by the factor of 2.8 are as follows:8.3.4 Repeatability standard deviation = 0.8.8.3.5 Reproducibility standard deviation = 2.5.8.4 BiasThis test method has no bias because the iodinevalue is defined only in terms of the test method.9. Keywords9.1 iodine value; tall oil fatty acids8Supporti
46、ng data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D01-1127.TABLE 1 Specimen WeightsIodine ValueNormal Fatty Acids, 100 to150 % Excess of Reagent, gConjugated Fatty Acids, 115 to135 % Excess of Reagent, gLess than 3 103 8.46 to 10.575 5.08
47、to 6.3510 2.54 to 3.1720 0.85 to 1.5940 0.64 to 0.7960 0.42 to 0.5380 0.32 to 0.40 0.34 to 0.3790 0.28 to 0.35 0.30 to 0.33100 0.25 to 0.32 0.27 to 0.30110 0.23 to 0.29 0.24 to 0.27120 0.21 to 0.26 0.22 to 0.25130 0.20 to 0.24 0.21 to 0.23140 0.18 to 0.23 0.19 to 0.21150 0.17 to 0.21 0.18 to 0.20160
48、 0.16 to 0.20 0.17 to 0.18170 0.15 to 0.19 0.16 to 0.17180 0.14 to 0.18 0.15 to 0.16D5768 02 (2010)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that dete
49、rmination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee
