1、Designation: D5554 15Standard Test Method forDetermination of the Iodine Value of Fats and Oils1This standard is issued under the fixed designation D5554; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、 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 determination of the iodinevalue of fats and oils.1.2 The values stated in SI units are to be regarded ass
3、tandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the a
4、pplica-bility of regulatory limitations prior to use.2. Significance and Use2.1 This test method is intended for the determination of theiodine value of fats and oils that do not contain conjugateddouble bonds. The iodine value is a measure of the unsaturationof fats and oils and is expressed in ter
5、ms of the number ofcentigrams of iodine absorbed per gram of sample.3. Apparatus and Reagents3.1 Glass-Stoppered Bottles or Wide Mouth ErlenmeyerFlasks, 500 mL. Wide mouth bottles or flasks are essential ifstirring is done by mechanical means.3.2 Glass-Stoppered Volumetric Flasks, conforming toNIST
6、tolerances2and accurately calibrated to contain 1000mL.3.3 Pipette, 20 mL.3.4 Two Pipettes, 25 mL. One pipette is reserved for usewith the standard potassium dichromate solution and shallconform to NIST tolerances2and be calibrated to deliver 25mL.3.5 Glacial Acetic Acid, A.C.S. grade. The permangan
7、atetest shall be applied to be sure that this specification is met.3.5.1 Two millilitres of the glacial acetic acid shall bediluted with 10 mL of distilled water and 0.1 mL of 0.1 NKMnO4shall be added. The pink color shall not be entirelydischarged within 2 h.3.6 Potassium Iodide, A.C.S. grade.3.7 C
8、hlorine, 99.8 %. Satisfactory commercial grades areavailable in cylinders, but this gas must be dried by passingthrough sulfuric acid (sp. gr. 1.84) before introducing into theiodine solution.3.7.1 Chlorine may be prepared by allowing hydrochloricacid (sp. gr. 1.19) to drop onto potassium permangana
9、te or ona mixture of potassium permanganate and manganese dioxide.The gas thus generated shall be led through a glass tube intosulfuric acid (sp. gr. 1.84) and then into the iodine solution.3.8 Carbon Tetrachloride, A.C.S. grade. (WarningCarbon Tetrachloride is a known carcinogen. It is toxic byinha
10、lation, ingestion and skin absorption. Always handle Car-bon Tetrachloride inside a fume hood. Use only with adequateventilation.3.9 Cyclohexane3, A.C.S. grade.3.10 Reagent for Diluting SamplePrepare by mixing freshcyclohexane and glacial acetic acid, 1:1, v/v. (After mixing,verify the absence of ox
11、idizable matter in the reagent byshaking 10 mL of the reagent with 1 mL of saturated aqueouspotassium dichromate solution and 2 mL of concentratedsulfuric acid: no green coloration should appear. A greencoloration indicates presence of oxidizable matter, so discardand remix using fresh cyclohexane.)
12、3.11 Hydrochloric Acid, A.C.S. grade, sp. gr. 1.19.3.12 Soluble Starch, of suitable sensitivity.3.12.1 The test for starch sensitivity shall be made byadding, while stirring, 200 mL of boiling water to a paste madewith1gofstarch in a small amount of water. After placing 5mL of this solution in 100 m
13、L of water, add 0.05 mL of 0.1 Niodine solution. The deep blue color produced must be dis-charged by 0.05 mL of 0.1 N sodium thiosulfate.3.13 Potassium Dichromate, A.C.S. grade, shall be finelyground and dried to constant weight at about 110C before1This test method is under the jurisdiction of ASTM
14、 Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.08 on Fats and Oils. This testmethod was developed in cooperation with the American Leather Chemists Assn.(Method H 32-1957).Current edition approved Sept. 1, 2015. Published October 2015. Originallyapproved in 1994. Last
15、previous edition approved in 2011 as D5554 95(2011).DOI: 10.1520/D5554-15.2Available from National Institute of Standards and Technology, (NIST),Gaithersburg, MD 20899.3Comparison study showed excellent agreement between Carbon Tetrachlorideand Cyclohexane (ISO/IUPAP Smalley program).Copyright ASTM
16、International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1using. (A standard sample of potassium dichromate with acertificate of analysis may be obtained from NIST.2Thissample is strongly recommended as the primary standard forthis test method. The dichromate
17、 should be treated as directedin the certificate of analysis accompanying the sample.)3.14 Sodium Thiosulfate(Na2S2O35H2O), A.C.S. grade.3.15 Iodine, A.C.S. grade.3.16 Potassium Iodide Solution, prepared by dissolving 150g in distilled water and making up to 1 L.3.17 Starch Indicator Solution, shall
18、 be prepared by makinga homogeneous paste of 10 g of soluble starch in cold distilledwater and adding to this 1 L of boiling distilled water withrapid stirring; cool. Salicylic acid (1.25 g/L) shall be added topreserve the indicator. If long storage is required, the solutionshall be kept in a refrig
19、erator at 4 to 10C (40 to 50F). Freshindicator shall be prepared when the end-point of the titrationfrom blue to colorless fails to be sharp.3.18 Standard Potassium Dichromate Solution, 0.1 N, shallbe prepared by dissolving 4.9035 g of finely ground and driedpotassium dichromate in distilled water i
20、n the 1000 mLvolumetric flask and making to volume at 25C.3.19 Sodium Thiosulfate Solution, 0.1 N, prepared by dis-solving 24.8 g of sodium thiosulfate in distilled water anddiluting to 1 L.3.19.1 Standardization of the ThiosulfatePipette 25 mL ofthe standard dichromate solution into Erlenmeyer flas
21、k orbottle. Add 5 mL of hydrochloric acid, 10 mL of potassiumiodide solution and rotate to mix. Allow to stand for 5 min andthen add 100 mL of distilled water. Titrate with sodiumthiosulfate solution, shaking continuously, until the yellowcolor has almost disappeared. Add 1 to 2 mL of indicator andc
22、ontinue titration, adding the thiosulfate solution slowly, untilthe blue color has just disappeared. The strength of the sodiumthiosulfate solution is expressed in terms of its normality.Normality of Na2S2O3solution 52.5mL Na2S2O3solution required(1)3.20 Wijs Solution4, prepared by dissolving 13.0 g
23、 of iodinein 1 L of glacial acetic acid. Gentle heat may be necessary topromote solution. Cool and remove a small quantity (100 to200 mL) and set aside in a cool place for future use. Pass drychlorine gas into the iodine solution until the original titrationis not quite doubled. A characteristic col
24、or change takes placein the Wijs solution when the desired amount of chlorine hasbeen added. This may be used to assist in judging the end point.Aconvenient procedure is to add a small excess of chlorine andbring back to the desired titration by addition of some of theoriginal iodine solution that w
25、as taken out at the beginning.The original iodine solution and the finished Wijs solution shallboth be titrated with Na2S2O3solution as directed in 4.6.NOTE 1All Wijs solutions are sensitive to temperature, moisture, andlight. Store them in a cool and dark place and never allow them to cometo a temp
26、erature much above 30C.4. Procedure4.1 Melt the sample, if not already completely liquid, andfilter through filter paper to remove any impurities and the lasttraces of water. (Care shall be taken not to exceed 10 to 15Cabove the sample melting point during melting and filtering.)The sample shall be
27、absolutely dry.4.2 Accurately weigh the sample into a 500-mL flask orbottle to which have been added 20 mLof CCl4or 15 mLof thecyclohexane + glacial acetic acid solution (reagent 3.10). Theweight of sample must be such that there will be an excess ofWijs solution of 50 to 60 % of the amount added, t
28、hat is, 100to 150 % of the amount absorbed. Table 1 is a convenient guidefor selecting the size of sample.4.3 Pipette 25 mL of the Wijs solution into the flaskcontaining the sample and swirl to ensure an intimate mixture.4.4 Prepare at least two blank determinations and conductwith each group of sam
29、ples simultaneously and similar in allrespects.4.5 Store the flasks in a dark place for 30 min at atemperature of 25 6 5C. (Store samples with an iodine valueabove 150, such as linseed and perilla oils, for 1 h.)4.6 From storage, remove the flasks and add 20 mL of KIsolution followed by 100 mL of di
30、stilled water. Titrate thesolution with 0.1 N Na2S2O3solution, adding gradually andwith constant shaking. (Mechanical stirring is very satisfactoryfor agitating during the addition of thiosulfate.) Continue thetitration until the yellow color has almost disappeared, add 1 to2 mL of starch indicator
31、solution, and continue the titrationuntil the blue color has just disappeared.5. Calculation5.1 Calculate the iodine value as follows:iodine value 5B 2 S! 3N 312.69weight of sample(2)where:B = titration of blank,S = titration of sample, andN = normality of Na2S2O3solution.4Wijs Solution (Iodine Mono
32、chloride Solution) may be purchased commercially.TABLE 1 Guide for Selecting Sample SizeIodine ValueSample Weight, gWeighingAccuracy, g100 % Excess 150 % Excess3 10 10 0.0013 10.5760 8.4613 0.0055 6.3460 5.0770 0.000510 3.1730 2.5384 0.000220 1.5865 0.8461 0.000240 0.7935 0.6346 0.000260 0.5288 0.42
33、31 0.000280 0.3966 0.3173 0.0001100 0.3173 0.2538 0.0001120 0.2644 0.2115 0.0001140 0.2266 0.1813 0.0001160 0.1983 0.1587 0.0001180 0.1762 0.1410 0.0001200 0.1586 0.1269 0.0001D5554 1526. Precision and Bias6.1 This test method is adopted from the procedures of theAmerican Leather ChemistsAssociation
34、 where it has long beenin use and was approved for publication before the inclusion ofprecision and bias statements was mandated. The originalinterlaboratory test data are no longer available. The user iscautioned to verify by the use of reference materials, ifavailable, that the precision and bias
35、(or reproducibility) of thistest method is adequate for the contemplated use.7. Keywords7.1 fats and oils; iodine value; leather; unsaturationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of thi
36、s standard are expressly advised that determination 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 yea
37、rs 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 commit
38、tee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM 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 1942
39、8-2959,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 01923, Tel: (978) 646-2600; http:/ 153
