1、Designation: D2807 93 (Reapproved 2009)1Standard Test Method forChromic Oxide in Leather (Perchloric Acid Oxidation)1This standard is issued under the fixed designation D2807; 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.This standard has been approved for use by agencies of the Department of Defense.1NOTEAdded research report information to Se
3、ction 12 editorially in September 2010.1. Scope1.1 This test method covers the determination 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 The values state
4、d in SI units are to be regarded asstandard. 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
5、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:2D2617 Test Method for Total Ash in LeatherD2813 Practice for Sampling Leather for Physical andChemical TestsE180 Practice for
6、Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals33. Summary of Test Method3.1 The perchloric acid method is applied to the ashobtained in Test Method D2617. In the acid digestion, anyremaining organic matter is destroyed and the chromiumoxidize
7、d 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 ash, but care must be takenbecause of potential hazards in the use of this reagent. Theperchlo
8、ric 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 present in quantity. The precision and accuracy ofthe methods are usually at least as good as the sa
9、mpling 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 providesadequate accuracy for this purpose.5. Apparatus5.1 Potentiometric Titration EquipmentThis i
10、s 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 variety of instruments is satisfac-tory.4The most convenient common feature of these instru-ments
11、 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 electrodes are immersedin the sample, the solution agitated by the stirrer, and thepotential b
12、alanced 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 tests. Unless otherwise indicated, it is intended that1This test method is under the jurisdiction
13、 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 Leather ChemistsAssn.Current edition approved April 1, 2009. Published July 2009. Originallyapproved in 1969. Last previous edit
14、ion approved in 2003 as D2807 93 (2003).DOI: 10.1520/D2807-93R09E01.2For referenced ASTM standards, visit the 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 w
15、ebsite.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.4Satisfactory equipment include, among others the 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 a
16、llow 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,add 2 mL of 2 % starch solution and continue titrating until thedeep blue color changes to a clear green. Record the titration.Calculate the normality
17、 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 The thiosulfate solution is quite stable but should berestandardized at least once a month.6.10 Starch Indicator Solution, prepared according to ac-ce
18、pted procedures available in analytical handbooks.6.11 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4).7. Hazards7.1 The improper use of HClO4can lead to violent andserious explosions. In general, these can be traced to situationswhere concentrated HClO4has come in contact with organic o
19、reasily oxidized materials.7.2 The exact procedures given must be followed and thedigestions, once started, should be kept from possible contactwith other organic matter. The digestions should never beallowed to boil dry. HClO4should never be used withoutaccompanying use of HNO3and H2SO4.7.3 All spi
20、lls 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 perchloric acid hood, reserved for perchlo-ric acid digestions, equipped with wash-down facilities andconstructed entirely of nonporous inorganic mat
21、erial 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 keep 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
22、in accordance with an accepted procedure,weighed and ashed according to Test Method D2617.5Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standar
23、ds for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.6A satisfactory reagent, Ferroin, is manufactured by the G. Frederick SmithChemical Co., Columbus, Ohio.D2807 93 (2009)129. P
24、rocedure9.1 Transfer the ash obtained from the determination of ash,Test Method D2617, to a 250-mLErlenmeyer flask.Add, in theorder named,20mLofHNO3, 15 mL of HClO4, and 10 mL ofH2SO4. Add a few glass beads. In the perchloric acid hood,heat gently under reflux conditions, using a small funnel as aco
25、ndenser in the neck of the flask, until all organic matter isdestroyed and the color changes to a clear red-orange, indicat-ing oxidation of chromium. 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
26、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 give a titration volume between theselimits and repeat the determination.9.2 Titration with Na2S2O3SolutionAdd 30 mL of H3PO4and 20 mL of KI solution to t
27、he 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 described 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 bl
28、ue color changes to a clear green.Record the titration. Calculate the results in accordance withSection 9.9.3 Titration with Ferrous Ammonium Sulfate SolutionAdd2mLofH3PO4and titrate with 0.1 N ferrous ammoniumsulfate solution standardized as described in 6.3.1. When thecolor of the solution has cha
29、nged from yellow through yel-lowgreen to blue-green, add 5 drops of indicator6and continuetitrating until the blue-green solution changes to a red-brown.Record titration. Calculate results as described in Section 10.9.4 Alternatively, the titration may be done potentiometri-cally. After adding the H
30、3PO4, transfer the solution to a 250-mL beaker and titrate with 0.1 N ferrous ammonium sulfatesolution, using the potentiometric apparatus described 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 pre
31、ferable to use the same method of determiningthe end point in both the standardization of the ferrousammonium sulfate solution and in the analysis of 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
32、 3 100/C! (3)where:A = millilitres of titrating solution used (either thiosulfateor ferrous ammonium sulfate),B = normality of titrating solution, andC = mass of leather. Use the mass of leather recorded asC B in Section 7 of Test Method D2617.10.2 The above calculation gives the Cr2O3content of the
33、leather 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 same leather at the same timeaccording to accepted procedures.7If D is the percentagemoisture found in the sample, calculate the Cr2O3, dry basis, %as
34、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 Cr2O3is performed on a leatherthat has been conditioned and weighed at constant temperatureand humidity, the fact should be indicated in reporting theresul
35、ts.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 % absolute are acceptablefor averaging (95 % confidence level).12. Precision and Bias812.1 ReproducibilityThe average difference between tworesults (each
36、 the average of duplicate determination) obtainedby analysts in different laboratories will approximate 0.06 %absolute. Two such values should be considered suspect (95 %confidence level) if they differ by more than 0.2 % absolute.12.2 BiasThe test method yields results that average1.75 % relative l
37、ow 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 in fivelaboratories.NOTE 2The estimates of checks for duplicates and reproducibility in12.1 and 12.2 are based on an interlaboratory study of four leat
38、hers run intriplicate in each of eight laboratories. The precision statements weredeveloped9using Practice E180.13. Keywords13.1 ash; chromic oxide; perchloric acid oxidation7Acceptable procedures are published in Journal of the American LeatherChemists Association, JALCA,Vol 51, 1956, p. 497; or Of
39、fcial Methods of Analysis,Am. Leather Chemists Assn., available through the Office of Secretary-Treasurer,TexasTech University, P.O. Box 45300, Lubbock,TX 79409; or see Practice D2813.8Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting RR:D31-10069The
40、 actual data upon which the results are based are reported in Journal,American Leather Chemists Assn. JALCA, Vol 54, 1959, p. 2.D2807 93 (2009)13ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of
41、this 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
42、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 com
43、mittee, 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 1
44、9428-2959,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 ASTM website (www.astm.org/COPYRIGHT/).D2807 93 (2009)14
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