1、Designation: D7967 16Standard Test Method forAnalysis of Chrome Content (as Cr2O3) in Wet Blue usingAtomic Absorption1This standard is issued under the fixed designation D7967; 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the Atomic Absorptionprocedure, using nitrous oxide-acetylene flame, to analyze thechrom
3、e content of Wet Blue on a moisture-free basis.1.2 The values stated 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
4、 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. Some specifichazards statements are given in Section 9 on Hazards and in12.5.2. Referenced Documents2.1 ASTM Standards:2D1517 Terminology Relat
5、ing to LeatherD6656 Test Method for Determination of Chromic Oxide inWet Blue (Perchloric Acid Oxidation)D6659 Practice for Sampling and Preparation of Wet Blueand Wet White for Physical and Chemical TestsD6658 Test Method for Volatile Matter (Moisture) of WetBlue by Oven DryingE177 Practice for Use
6、 of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions: For Definitions of general leather and tan-ning terms used in this test method refer to TerminologyD1517.4. Summary of Te
7、st Method4.1 The chromium content measured as Cr2O3is determinedin Wet Blue using Atomic Absorption (AA). The Wet Blue isdigested using oxalic acid, hydrochloric acid, and potassiumchloride. The chromium content in Wet Blue is measured at awavelength of 429 nanometers with a 0.7 slit using AtomicAbs
8、orption with a nitrous oxide/acetylene flame. After the AAreading the chromium content is determined on a moisture-freebasis.5. Significance and Use5.1 The procedure described is for chromium in Wet Blueusing Atomic Absorption. This method may be used to deter-mine the chromium content in Wet Blue a
9、s an alternate to TestMethod D6656.5.2 The chromium content of Wet Blue is related to thedegree of tannage obtained, and hence may be a matter forspecification in the purchase of Wet Blue. The proceduredescribed provides adequate accuracy for this purpose.6. Interferences6.1 The nitrous oxide/acetyl
10、ene flame reduces or eliminatesmany chemical or compound interferences that can occur if justan air/acetylene flame is used, however, sensitivity may bereduced.7. Apparatus7.1 Atomic Absorption analyzer using a nitrous oxide-acetylene flame measuring at a wavelength of 429 nanometerswith a slit of 0
11、.7 mm.NOTE 1Follow manufacturers recommendations for using nitrousoxide-acetylene flame conditions.7.2 Analytical Balance, accurate and calibrated to 0.001 g.7.3 Leather Cutting Tool, (such as scissors or razor blade).7.4 Beaker, 250 mL capacity or equivalent.7.5 Beaker, 1000 mL capacity or equivale
12、nt.7.6 Volumetric Flask, 200 mL capacity or equivalent.7.7 Volumetric Flask, 1000 mL capacity or equivalent.7.8 Erlenmeyer Flask, 1 L capacity, or equivalent.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.02 on Wet Blu
13、e.Current edition approved Sept. 1, 2016. Published October 2016. DOI: 10.1520/D7967-16.2For 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 Summa
14、ry page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17.9 Watch Glass.7.10 Hot Plate, to be placed inside exhaust or fume hood.7.11 Desiccator.8. Reagents and Materials8.1 Purity of ReagentsAnalytical Reagent (AR)
15、 Gradeshall be used in all tests. Unless otherwise indicated, it isintended that all reagents conform to the specifications of theCommittee on Analytical Reagents of the American ChemicalSociety (ACS), where such specifications are available.3Othergrades may be used, provided it is first ascertained
16、 that thereagent is of sufficiently high purity to permit its use withoutlessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean distilled or deionizedwater.8.3 Commercial ReagentsThe use of commercially avail-able pre-
17、standardized analytical reagents and solutions isappropriate, providing those reagents and solutions have beenprepared according to and conform to the previously men-tioned specifications (see 8.1).8.4 Oxalic Acid (H2C2O4).8.5 Hydrochloric Acid (HCl).8.6 Potassium Chloride (KCl).8.7 Potassium Dichro
18、mate (K2Cr2O7)Used in standardCr2O3solution.8.8 Sulfuric Acid (H2SO4), 96-98 % w/wUsed to preparestandard Cr2O3solution.8.9 Sodium Bisulfite (NaHSO3).8.10 Wet Blue Digestion Mixture.NOTE 2Wet Blue Digestion Mixture must be prepared in a Fume orExhaust Hood.8.10.1 Add approximately 400 mL of water to
19、 a 500 mL (orlarger) container.8.10.2 Place container on stirrer with stir bar in water. Turnstirrer on.8.10.3 Add 16 g oxalic acid to container and stir until fullydissolved.8.10.4 Slowly add 56 mL concentrated hydrochloric acid(HCl).8.10.5 Allow solution to stir at least 5 min.8.10.6 Add 13.0 g po
20、tassium chloride (KCl).8.10.7 Dilute to 500 mL with water.8.10.8 Allow solution to stir until the potassium chloride(KCl) has visually dissolved. if the KCl does not dissolve,slightly heat the solution. Once dissolved, remove from heatand cool to room temperature before use.8.11 Commercial Cr Standa
21、rd, 1000 ppm:8.11.1 Using a commercially available 1000 ppm Cr Stan-dard solution, make a 10 ppm Cr solution which will be usedto verify the concentration of the prepared Cr2O3standard in8.12. To convert from Cr to Cr2O3, multiply by a factor of1.462 (A 10 ppm Cr solution equates to a 14.62 ppm Cr2O
22、3solution).8.12 Standard Cr2O3solution (1000 ppm):8.12.1 Dry approximately 5.0 g potassium dichromate(K2Cr2O7) at 100C overnight. Then cool the dried potassiumdichromate (K2Cr2O7) to room temperature in a desiccator.8.12.2 Weight exactly 1.9356 g of oven dried K2Cr2O7andput in a 1000 mL beaker.8.12.
23、3 Add 500 mL water and stir until dissolved.8.12.4 Carefully add 5 mL of concentrated sulfuric acid(H2SO4) while stirring.NOTE 3Perform in fume hood or exhaust hood, especially whenadding acids.8.12.5 Slowly add5gofsodium bisulfite (NaHSO3) whilestirring.8.12.6 Place beaker with stirring rod in it o
24、n the hot plate.8.12.7 Add 50 g oxalic acid while stirring.8.12.8 Bring solution to boiling (or near boiling) for 15 min.8.12.9 Remove from the hot plate and add 300 mL of waterwhile stirring. When cooled to room temperature, transfersolution to a 1000 mL volumetric flask, rinsing beaker com-pletely
25、 and into the flask with water.8.12.10 Bring to volume, 1000 mL, with water and mixwell. Verify Cr2O3content according to 8.13. Store accordingto good laboratory practices.8.12.11 Pipet 1 mL of the 1000 ppm Cr2O3solution into avolumetric flask and dilute to 100 mL with water. Invert andmix well. Use
26、 this as a 10 ppm Cr2O3standard solution.8.12.12 Pipet 5 mL of the 1000 ppm Cr2O3solution into avolumetric flask and dilute to 200 mL with water. Invert andmix well. Use this as a 25 ppm Cr2O3standard solution.NOTE 4Prepare the 10 ppm and 25 ppm Cr2O3standard solution freshdaily (on day of use).8.13
27、 Calibration and Standardization:8.13.1 Using water to zero the AA, create a calibrationcurve with the 10 ppm and the 25 ppm Cr2O3standards from8.12.11 and 8.12.12. respectively.8.13.2 Obtain a reading from the AA for the 10 ppmcommercial Cr solution. This should be 14.6 ppm (60.3 ppm)Cr2O3, if the
28、standard solution prepared in 8.12 is accurate. Ifnot, the solution will need to be discarded and remade. Oncethe 1000 ppm Cr2O3standard solution is deemed acceptable,retain this standard stock solution for future use. Verify 8.12every 6 months with commercial standard (8.11) to ensurestandard stock
29、 solution is still viable. If the results after 6months are not within 60.3 ppm of the commercial standard,remake your standard stock solution according to 8.12.9. Hazards9.1 Chemicals used can be harmful.3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washing
30、ton, 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), Rockville,MD.D7967 1629.2
31、 The exact procedures given must be followed and thedigestion, once started, should be kept from possible contactwith other organic matter. The digestion should never beallowed to boil dry.10. Sampling, Test Specimens, and Test Units10.1 The test specimen shall be 0.2 to 0.3 g of Wet Bluefrom a comp
32、osite sample prepared according to PracticeD6659, Method A, weighed to an accuracy of 0.001 g andperformed in duplicate, or10.2 The test specimen shall be 0.1 to 0.15 g of Wet Bluefrom a composite sample prepared according to PracticeD6659, Method B, weighed to an accuracy of 0.001 g andperformed in
33、 duplicate.11. Preparation of Apparatus11.1 Turn on Atomic absorption machine. Using a nitrousoxide-acetylene flame, optimize the AA at a wavelength of 429nanometers with a 0.7 mm slit.12. Procedure12.1 Weigh a sample according to Test Method D6658 todetermine the percent moisture in the specimen. T
34、his must bedone concurrently with the other sample weights to eliminatemoisture loss between samples. The percent moisture valuewill be used for the calculation (see Section 13) for percentCr2O3on a moisture-free basis (MFB).12.2 Cut and weigh the test specimen (see 10.1) or weighthe dry specimen (s
35、ee 10.2) to the nearest 0.001 g, and recordthe weight as “W.”12.3 Place sample in a labeled 250 mL beaker.12.4 Add 25 mL of Wet Blue digestion mixture, from 8.10.12.4.1 Place a watch glass over the beaker.12.5 Boil sample on a hot plate in a fume hood until samplehas completely digested (approximate
36、ly 10 to 15 min, someinsoluble residue may remain). (WarningDO NOT BOILDRY.)12.6 Remove from hot plate and allow to cool.12.7 Rinse watch glass and sides of beaker with water intothe beaker.12.8 Dilute to 200 mL in a volumetric flask with water andmix well.12.9 Using a nitrous oxide-acetylene flame,
37、 optimize theAA at a wavelength of 429 nanometers with a 0.7 mm slit.12.10 Using water as a blank, obtain a calibration curve asin 8.13.1.12.11 Run sample through AA and record reading as “A.”12.12 Calculate chrome content on a moisture-free basis.13. Calculation or Interpretation of Results13.1 Obt
38、ain the percent Cr2O3(MFB) as follows:ppmCr2O310 0005 %Cr2O3(1)13.2 Simplified:A 30.02W5 %Cr2O3(2)%Cr2O3100 2 % Moisture!1005 %Cr2O3MFB! (3)where:A = ppm reading from AA (12.11),W = weight of sample in grams (12.2),ppm = parts per million, andMFB = moisture-free basis (12.1).14. Report14.1 Report th
39、e percentage of Cr2O3on a moisture-freebasis for each replicate and the average of the replicates.15. Precision and Bias15.1 The precision of this test method is based on aninterlaboratory study of ASTM WK39120, New Standard TestMethod for Analysis of Chrome Content (as Cr2O3)inWetBlue Using Atomic
40、Absorption, conducted in 2011. A total ofthree laboratories participated in this study, testing a single WetBlue material. Each “test result” reported represents an indi-vidual determination. All participants were asked to reportduplicate test results, as well as an average. Practice E691 wasfollowe
41、d for the design and analysis of the data; the details aregiven in an ASTM Research Report.415.1.1 Repeatability (r)The difference between repetitiveresults obtained by the same operator in a given laboratoryapplying the same test method with the same apparatus underconstant operating conditions on
42、identical test material withinshort intervals of time would in the long run, in the normal andcorrect operation of the test method, exceed the followingvalues only in one case in 20.15.1.1.1 Repeatability can be interpreted as maximum dif-ference between two results, obtained under repeatabilitycond
43、itions, that is accepted as plausible due to random causesunder normal and correct operation of the test method.15.1.1.2 Repeatability limits are listed in Table 1.15.1.2 Reproducibility (R)The difference between twosingle and independent results obtained by different operatorsapplying the same test
44、 method in different laboratories usingdifferent apparatus on identical test material would, in the long4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D31-1023. ContactASTM CustomerService at serviceastm.org.TABLE 1 Chrome Cont
45、ent as Cr2O3(%)MaterialAverageARepeatabilityStandardDeviationSrReproducibilityStandardDeviationSRRepeatabilityLimitrReproducibilityLimitRWetBlue3.115 0.058 0.135 0.161 0.377AThe average of the laboratories calculated average.D7967 163run, in the normal and correct operation of the test method,exceed
46、 the following values only in one case in 20.15.1.2.1 Reproducibility can be interpreted as maximumdifference between two results, obtained under reproducibilityconditions, that is accepted as plausible due to random causesunder normal and correct operation of the test method.15.1.2.2 Reproducibilit
47、y limits are listed in Table 1 andTable 2.15.1.3 The above terms (repeatability limit and reproduc-ibility limit) are used as specified in Practice E177.15.1.4 Any judgment in accordance with 15.1.1 and 15.1.2would have an approximate 95 % probability of being correct.15.2 BiasNo reference materials
48、 were tested as part of thisstudy, therefore no statement on bias can be made at this time.15.3 The precision statement was determined through sta-tistical examination of 26 test results, submitted by threelaboratories, measuring a single material.15.4 The following results, Table 3, were obtained w
49、hen thesame laboratory tested the same sample using an existingASTM standard, D6656, and the atomic absorption method:16. Keywords16.1 AA; atomic absorption; chrome content; chromic ox-ide; chromium; Wet BlueASTM 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 rights, are entirely their own responsibility.This standard is subject to
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