1、Designation: D5768 02 (Reapproved 2014)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7、 (Withdrawn 2006)3D1959 Test Method for Iodine Value of Drying Oils andFatty Acids (Withdrawn 2006)3E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision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
8、iodine value of a fatty acid product 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 rea
9、gent. The amount ofreagent absorbed 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. Wh
10、ereno conjugation is present, the 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 i
11、n Test MethodD1959 with the less hazardous 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
12、 than tall oil fatty acid but that possibility has notbeen investigated.4. Apparatus4.1 BottlesGlass-stoppered bottles or Erlenmeyer flasks of250-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 unles
13、s otherwise specified. Unless otherwiseindicated, 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 d
14、irect responsibility ofSubcommittee D01.34 on Pine Chemicals and Hydrocarbon Resins.Current edition approved Dec. 1, 2014. Published December 2014. Originallyapproved in 1995. Last previous edition approved in 2010 as D5768 02 (2010).DOI: 10.1520/D5768-02R14.2For referenced ASTM standards, visit the
15、 ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM Int
16、ernational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1American 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 lesseni
17、ng the accuracy of the determi-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 o
18、fthe acid with 10 mL of 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 sup
19、pli-ers Material Safety 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 concentrat
20、ed hydro-chloric acid (HCl, 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 di
21、lute to 1 L.5.7 Sodium Thiosulfate, 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 beenfine
22、ly ground and then dried 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. Tit
23、rate with the Na2S2O3solution, 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 hasjust disappeared. Calculate the normality, N, of the Na2S2O3asfollows:
24、N 5 A 320.39!/C (1)where:A =K2Cr2O7used, g, andC =Na2S2O3solution required for titration of the K2Cr2O7,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
25、 of boiling water.Dilute 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. Sti
26、r rapidly andcool. Salicylic 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: E
27、xtremely hazardous. Forspecific 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.
28、 Pass dry chlorine gas 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 sma
29、ll excess of chlorine 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
30、1Iodine monochloride (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 i
31、t is not already liquid (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
32、excess of Wijs solution of 1256 10 % for conjugated fatty acids and 125 6 25 % for normalor nonconjugated fatty acids. Specimen weights meeting thisrequirement are shown in Table 1. Add 20 mL of iso-octaneand swirl to dissolve.4Reagent Chemicals, American Chemical Society Specifications, AmericanChe
33、mical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Roc
34、kville,MD.5“Analytical Reagents, ACS Specifications,” American Chemical Society,Washington, DC, 1960.6National Institute of Standards and Technology Standard Reference MaterialNo. 136 of potassium dichromate is recommended for this purpose and should betreated as directed in the certificate of analy
35、sis accompanying the standard sample.Available from NIST, Gaithersburg, MD.7Graupner, A. J., and Aluise, V. A., “A New Rapid Titration Method forDetermining the Halogen Ratio of Wijs Solution and of Iodine Monochloride,”Journal, American Oil ChemistsSoc., February 1966, p. 81.D5768 02 (2014)26.3 Pip
36、et 25 mL of Wijs solution 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 6
37、5C.6.4 Remove the flasks 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 solutiona
38、nd continue the titration 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 312.69#/S (2)where:V =Na2S2O3solution required for titration
39、of the specimen,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
40、 in 2000. One of 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
41、within and between 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 Repeatabilit
42、y limit, 95 % (within 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 fact
43、or of 2.8 are as 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 informationgiven below for the iodine value is for the comparison of twotest results each of which is the average of three test determi-n
44、ations as follows: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, rel
45、ated to the abovenumbers 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 fatt
46、y acidsASTM 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 determination of the validity of any such patent rights, and the riskof infringement of such righ
47、ts, 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
48、standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM
49、Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01
