1、Designation: D 2807 93 (Reapproved 2003)Standard Test Method forChromic Oxide in Leather (Perchloric Acid Oxidation)1This standard is issued under the fixed designation D 2807; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method covers the de
3、termination of chromicoxide in leathers that have been partly or completely tannedwith chromium compounds. In general the samples will con-tain between 1 and 5 % chromium, calculated as chromicoxide.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its
4、use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. See Section 7 forspecific safety hazards.2. Referenced Documents2.1 ASTM Standards:D 2617 Test Method for Total Ash
5、 in Leather2D 2813 Practice for Sampling Leather for Physical andChemical Tests2E 180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial SpecialtyChemicals33. Summary of Test Method3.1 The perchloric acid method is applied to the ashobtained in Test Method D
6、 2617. In the acid digestion, anyremaining organic matter is destroyed and the chromiumoxidized to the hexavalent state. On dilution, the chromium istitrated volumetrically with thiosulfate or ferrous salt. Theperchloric acid method requires less manipulation than proce-dures based on fusion of the
7、ash, but care must be takenbecause of potential hazards in the use of this reagent. Theperchloric acid method also tends to give low results.4. Significance and Use4.1 The procedure described is specific for chromium inleather. Vanadium is the only common interfering element andthis is rarely presen
8、t in quantity. The precision and accuracy ofthe methods are usually at least as good as the sampling of theleather itself.4.2 The chromium content of leather relates to the degree oftannage obtained, and hence may be a matter for specificationin the purchase of leather. The procedure described provi
9、desadequate accuracy for this purpose.5. Apparatus5.1 Potentiometric Titration EquipmentThis is required inan alternative method for titrating chromium (Cr6+) withferrous ammonium sulfate solution. The equipment consists of:5.1.1 Stirrer.5.1.2 Calomel and Platinum Electrodes.5.1.3 PotentiometerA var
10、iety of instruments is satisfac-tory.4The most convenient common feature of these instru-ments is a null-point device (either a cathode-ray electron tubeor galvanometer) that will signal the abrupt change occurringin the potential when the end point is reached.5.2 In carrying out the titration, the
11、electrodes are immersedin the sample, the solution agitated by the stirrer, and thepotential balanced with the galvanometer or cathode-ray tube.Titrant is added dropwise until a sharp permanent change inpotential occurs.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tes
12、ts. Unless otherwise indicated, it is intended thatall reagents shall conform to specifications of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications are available.5Other grades may beused, provided it is first ascertained that the reagent is ofsufficientl
13、y high purity to permit its use without lessening theaccuracy of the determination.1This test method is under the jurisdiction ofASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis Thistest method was developed in cooperation with the American Le
14、ather ChemistsAssn.Current edition approved May 10, 2003. Published June 2003. Originallyapproved in 1969. Last previous edition approved in 1998 as D 2807 93 (1998).2Annual Book of ASTM Standards, Vol 15.04.3Annual Book of ASTM Standards, Vol 15.05.4Satisfactory equipment include, among others the
15、following: the Kelley,Serfass, and Fisher tritrimeters, Leeds add 4 mL of hydrochloric acid (HCl, 1+1) 20 mLof KI solution, stopper the flask, and allow to stand 5 min in thedark. Titrate with the thiosulfate solution to be standardized.When the color of the solution has faded to a brownish-green,ad
16、d 2 mL of 2 % starch solution and continue titrating until thedeep blue color changes to a clear green. Record the titration.Calculate the normality of the thiosulfate solution as follows:Normality 5 A/0.04903 3 B! (2)where:A = grams of K2Cr2O7used, andB = millilitres required for titration.6.9.2 Th
17、e thiosulfate solution is quite stable but should berestandardized at least once a month.6.10 Starch Indicator Solution, prepared according to ac-cepted procedures available in analytical handbooks.6.11 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4).7. Hazards7.1 The improper use of HCl
18、O4can lead to violent andserious explosions. In general, these can be traced to situationswhere concentrated HClO4has come in contact with organic oreasily oxidized materials.7.2 The exact procedures given must be followed and thedigestions, once started, should be kept from possible contactwith oth
19、er organic matter. The digestions should never beallowed to boil dry. HClO4should never be used withoutaccompanying use of HNO3and H2SO4.7.3 All spills involving HClO4should be flushed with water.Rags, sawdust, and other organic materials should never beused to mop up spilled acid.7.4 The use of a p
20、erchloric acid hood, reserved for perchlo-ric acid digestions, equipped with wash-down facilities andconstructed entirely of nonporous inorganic material is re-quired.7.5 Perchloric acid bottles should be stored on a ceramictray or shelf and never on a wooden or pervious shelf. It isadvisable to kee
21、p only one 1-lb (0.45-kg) bottle of acid in theworking area.8. Test Specimen8.1 The specimen shall be 2 g leather from the compositesample prepared in accordance with an accepted procedure,weighed and ashed according to Test Method D 2617.9. Procedure9.1 Transfer the ash obtained from the determinat
22、ion of ash,Test Method D 2617, to a 250-mL Erlenmeyer flask. Add, inthe order named,20mLofHNO3, 15 mLof HClO4, and 10 mLof H2SO4. Add a few glass beads. In the perchloric acid hood,heat gently under reflux conditions, using a small funnel as acondenser in the neck of the flask, until all organic mat
23、ter is5Reagent 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 LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pha
24、rmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.6A satisfactory reagent, Ferroin, is manufactured by the G. Frederick SmithChemical Co., Columbus, Ohio.D 2807 93 (2003)2destroyed and the color changes to a clear red-orange, indicat-ing oxidation of chromium
25、. Heat an additional 2 min, coolquickly, rinse and remove funnel, and dilute to 125 mL withwater. Heat to boiling and continue boiling for 7 min. Cool andtitrate by the procedure given in 9.2or9.3.NOTE 1If the titration volume is less than 5 mL or more than 50 mL,adjust the size of the sample to giv
26、e a titration volume between theselimits and repeat the determination.9.2 Titration with Na2S2O3SolutionAdd 30 mL of H3PO4and 20 mL of KI solution to the solution obtained in 9.1 andstopper the flask.Allow to stand 5 min in the dark. Titrate with0.1 N sodium thiosulfate solution standardized as desc
27、ribed in6.9.1. When the color of the solution hasfaded to a brownish-green, add 2 mL of 2 % starch solution and continue thetitration until the deep blue color changes to a clear green.Record the titration. Calculate the results in accordance withSection 9.9.3 Titration with Ferrous Ammonium Sulfate
28、 SolutionAdd2mLofH3PO4and titrate with 0.1 N ferrous ammoniumsulfate solution standardized as described in 6.3.1. When thecolor of the solution has changed from yellow through yel-lowgreen to blue-green, add 5 drops of indicator6and continuetitrating until the blue-green solution changes to a red-br
29、own.Record titration. Calculate results as described in Section 10.9.4 Alternatively, the titration may be done potentiometri-cally. After adding the H3PO4, transfer the solution to a 250-mL beaker and titrate with 0.1 N ferrous ammonium sulfatesolution, using the potentiometric apparatus described
30、in 5.1.The end point is signalled by a sudden large change inpotential. Record the titration. Calculate results as described inSection 10.9.5 It is preferable to use the same method of determiningthe end point in both the standardization of the ferrousammonium sulfate solution and in the analysis of
31、 the sample.10. Calculation10.1 Calculate the chromium content as percentage ofchromic oxide (Cr2O3) in the leather as follows:Cr2O3,%5 A 3 B 3 0.02533 3 100/C! (3)where:A = millilitres of titrating solution used (either thiosulfateor ferrous ammonium sulfate),B = normality of titrating solution, an
32、dC = mass of leather. Use the mass of leather recorded asC B in Section 7 of Test Method D 2617.10.2 The above calculation gives the Cr2O3content of theleather on an “as weighed” basis. If it is desired to express thison a dry basis, a moisture determination should be run on asample weighed from the
33、 same leather at the same timeaccording to accepted procedures.7If D is the percentagemoisture found in the sample, calculate the Cr2O3, dry basis, %as follows:Cr2O3,%5 A 3 B 3 0.02533 3 100/C! 3 1/1 2 D/100!#! (4)where A, B, and C have the same significance as above.10.3 If the determination of Cr2
34、O3is performed on a leatherthat has been conditioned and weighed at constant temperatureand humidity, the fact should be indicated in reporting theresults.11. Report11.1 Report the following information.11.1.1 Report the percentage of Cr2O3to the nearest 0.1 %.Duplicate runs that agree within 0.09 %
35、 absolute are acceptablefor averaging (95 % confidence level).12. Precision and Bias12.1 ReproducibilityThe average difference between tworesults (each the average of duplicate determination) obtainedby analysts in different laboratories will approximate 0.06 %absolute. Two such values should be con
36、sidered suspect (95 %confidence level) if they differ by more than 0.2 % absolute.12.2 BiasThe test method yields results that average1.75 % relative low when compared to a standard sample ofNBS K2Cr2O7. The 99 % confidence limits on this value are1.50 to 2.00 % as determined by triplicate analyses
37、in fivelaboratories.NOTE 2The estimates of checks for duplicates and reproducibility in12.1 and 12.2 are based on an interlaboratory study of four leathers run intriplicate in each of eight laboratories. The precision statements weredeveloped8using Practice E 180.13. Keywords13.1 ash; chromic oxide;
38、 perchloric acid oxidationASTM 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 infrin
39、gement 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
40、 or for additional 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
41、 known to the ASTM Committee on Standards, at the address shown below.7Acceptable procedures are published in Journal of the American LeatherChemists Association, JALCA,Vol 51, 1956, p. 497; or Offcial Methods of Analysis,Am. Leather Chemists Assn., available through the Office of Secretary-Treasure
42、r,Texas Tech University, P.O. Box 45300, Lubbock, TX 79409; or see PracticeD 2813.8The actual data upon which the results are based are reported in Journal,American Leather Chemists Assn. JALCA, Vol 54, 1959, p. 2.D 2807 93 (2003)3This standard is copyrighted by ASTM International, 100 Barr Harbor D
43、rive, 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).D 2807 93 (2003)4
