1、Designation: D6657 16Standard Test Method forpH of Wet Blue and Wet White1This standard is issued under the fixed designation D6657; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses
2、 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 pH ofall types of Wet Blue and Wet White.1.2 The values stated in SI units are to be regarded asstandard. N
3、o 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 applica-bil
4、ity of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D6659 Practice for Sampling and Preparation of Wet Bluefor Physical and Chemical TestsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study t
5、oDetermine the Precision of a Test Method3. Terminology3.1 Definitions of Term Specific to this Standard:3.1.1 The pH of a solution has been defined as the negativelogarithm of the hydrogen ion activity. A solution of pH 7 isneutral at 24 C. Lower numbers indicate increasing acidity;higher numbers,
6、increasing alkalinity.4. Significance and Use4.1 This test method is designed to measure the pH of adistilled-water extract of Wet Blue and Wet White. This isconsidered to be a measure of the acidity or alkalinity of theWet Blue or Wet White. Excessive acidity or alkalinity mayhave a deleterious eff
7、ect on the aging characteristics of WetBlue and Wet White and the leather made from it.4.2 This test method is suitable for development, control,and service evaluation of wet blue.5. Apparatus5.1 Electronic pH Meter, with a suitable electrode. Themeter shall have an accuracy of at least 0.01 pH unit
8、 andreproducibility of 0.05 pH unit.5.2 Analytical Balance, sensitive to 0.01 g or greater.6. Reagents6.1 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean distilled water or water ofequal purity. Distilled water shall have a pH value of not lessthan 5.5 nor m
9、ore than 7.0 and shall give a residue of not morethan 0.5 mg, when 100 mL is evaporated and dried in aplatinum dish.6.2 Commercially Standardized pH Solutions3:6.2.1 Alkaline Phosphate Buffer Solution (0.01 M trisodiumphosphate, pH = 11.72 at 25 C)Dissolve 1.42 g of anhy-drous disodium hydrogen phos
10、phate (Na2HPO4) in 100 mL ofa 0.1 N carbonate-free solution of sodium hydroxide (NaOH)and dilute to 1 L with water.6.2.2 Borax Buffer Solution (0.01 M, pH = 9.18 at 25C)Dissolve 3.81 g of sodium tetraborate decahydrate(Na2B4O7 10H2O) in water and dilute to 1 L.6.2.3 Hydrochloric Acid (pH = 1.10 at 2
11、5 C)Add2gofconcentrated hydrochloric acid (HCl, sp gr 1.19) to 450 g ofwater. Standardize and dilute to 0.1 N.6.2.4 Phosphate Buffer Solution (0.025 M with respect toeach phosphate, salt pH = 6.86 at 2.5 C)Dissolve 3.40 g ofmonobasic potassium phosphate (KH2PO4) and 3.55 g ofanhydrous dibasic sodium
12、 phosphate (Na2HPO4) in water anddilute to 1 L.6.2.5 Potassium Hydrogen Phthalate Buffer Solution (0.05M, pH = 4.01 at 25 C)Dissolve 10.21 g of potassiumhydrogen phthalate (KHC8H4O4) in water and dilute to 1 L.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the dir
13、ect responsibility of Subcommittee D31.02 on Wet Blue.Current edition approved June 1, 2016. Published June 2016. Originallyapproved in 2001. Last previous edition approved in 2014 as D6657 - 14a1. DOI:10.1520/D6657-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact A
14、STM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Commercial buffer salts and solutions prepared in accordance with NationalBureau of Standards recommendations are sold by reputable laborator
15、y supplyhouses and may be used.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17. Test Specimen7.1 The specimen shall consist of a composite sampleprepared according to Practice D6659.7.1.1 Practice D6659Sample Preparation Method A (a
16、sreceived in wet state, diced): use 10 6 1g.7.1.2 Practice D6659Sample Preparation Method B(oven or air dried, ground): use2-5g.8. Standardization8.1 Use manufacturers directions for establishing two pointstandardization with standard pH solutions that read on eitherside of the anticipated pH of the
17、 solution to be tested. Washelectrodes by immersing in three changes of water and estab-lish a fresh liquid junction after blotting electrodes if usingsleeve type electrode prior to testing each solution.8.2 Check for electrode drift with either of the buffers andrestandardize if necessary.9. Proced
18、ure9.1 Weigh the specimen to the nearest 0.01 g and transfer toa 250 mL Erlenmeyer flask.9.1.1 If specimen was obtained as in 7.1.1 add water in theamount of ten times the mass of the specimen.9.1.2 If specimen was obtained as in 7.1.2 add water in theamount of twenty times the mass of the specimen.
19、9.1.3 Stopper the flask and agitate thoroughly. Let stand atthe Standard Laboratory Temperature, 23.0 6 1C (73.4 61.8F), with occasional agitation for not less than 4 nor morethan 24 h. Agitate thoroughly and if necessary transfer to aclean beaker or decant if possible.9.2 Determine the pH of the We
20、t Blue (or Wet White) watermixture or solution, reading the meter to the closest 0.05 unit.9.3 If a pH difference figure (Delta pH) is desired, removea 5 ml to 10 ml aliquot of the liquid into a beaker and dilute tenfold. Mix well and determine the pH. Calculate the differencein pH from the initial
21、reading.NOTE 1If the pH difference figure is 0.7 or greater, it is an indicationthat strong free acid is present.10. Report10.1 Report the following information:10.1.1 The pH of the sample shall be reported to the nearest0.05 pH unit.10.1.2 The pH difference figure (Delta pH) shall be reportedto the
22、 nearest 0.05 pH unit.11. Precision and Bias11.1 This test method is adopted from the leather tanningindustry where it has long been in use and approved fordissemination as a standard method before the inclusion ofprecision and bias statements was mandated. The pH of WetBlue can change significantly
23、 over time after removal from thechrome-tanning vessel. This change happens because chemicalreactions involving the basicity of the chromium sulfatecomplex continue to occur within the Wet Blue. The amountand rate of these pH changes is dependent on the specificprocesses and materials used to manufa
24、cture the Wet Blue. Theuser is cautioned to verify that the precision and bias (orreproducibility) of this method is adequate for the contem-plated application.11.2 A real world precision statement was determinedthrough statistical examination4of 145 results from 9laboratories, on 16 materials over
25、nearly 2 years. Practice E691was followed for the design and analysis of the data. The termsbelow (repeatability and reproducibility) are used as specifiedin Practice E177.11.2.1 Repeatability (r)The difference between repetitiveresults obtained by the same operator in a given laboratoryapplying the
26、 same test method with the same apparatus underconstant operating conditions on 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 20.11.2.2 Reproducibility (R)the differen
27、ce between twosingle and independent results obtained by different operatorsapplying the same test method in different laboratories usingdifferent apparatus on identical test material would, in the longrun, in the normal and correct operation of the test method,exceed the following values only in on
28、e case in 20.Repeatability (r) Reproducibility (R)0.04 0.2911.3 The precision of this test method is based on anintralaboratoy study of ASTM WK40322, New Standard TestMethod for the Determination of pH in Wet Blue and WetWhite, conducted in 2012. Nine laboratories participated in thisstudy, testing
29、16 Wet Blue samples. Every “test result” repre-sents an individual determination. The laboratories were askedto report a single test result for 13 materials and duplicate testresults for 3 materials. Except for the absence of replicate testresults from all of the study materials, Practice E691 wasfo
30、llowed for the design and analysis of the data; the details aregive in an ASTM research report.411.3.1 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
31、 on 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 20.11.3.1.1 Repeatability can be interpreted as maximum dif-ference between two results, obtained under repeatability
32、conditions, that is accepted as plausible due to random causesunder normal and correct operation of the test method.11.3.1.2 Repeatability limits are listed in Table 1.11.3.2 Reproducibility (R)The difference between twosingle and independent results obtained by different operatorsapplying the same
33、test method in different laboratories usingdifferent apparatus on identical test material would, in the longrun, in the normal and correct operation of the test method,exceed the following values only in one case in 20.4Supporting data have been filed at ASTM International Headquarters and maybe obt
34、ained by requesting Research Report RR:D31-1021. ContactASTM CustomerService at serviceastm.org.D6657 16211.3.2.1 Reproducibility can be interpreted as maximumdifference between two results, obtained under reproducibilityconditions, that is accepted as plausible due to random causesunder normal and
35、correct operation of the test method.11.3.2.2 Reproducibility limits are listed in Table 1.11.3.3 The above terms (repeatability limit and reproduc-ibility limit) are used as specified in Practice E177.11.3.4 Any judgment in accordance with 11.3.1 wouldnormally have an approximate 95 % probability o
36、f beingcorrect, however the precision statistics obtained in this ILSmust not be treated as exact mathematical quantities which areapplicable to all circumstances and uses. The limited numberof materials for which replicate results were reported essen-tially guarantees that there will be times when
37、differencesgreater than predicted by the ILS results will arise, sometimeswith considerably greater or smaller frequency than the 95 %probability limit would imply. Consider the repeatability limitas a guide, and the associated probability of 95 % as only arough indicator of what can be expected.11.
38、4 BiasNo information can be presented on the bias ofthe procedure in Test Method D6657 for measuring pH becauseno material having an accepted reference value was included inthe analysis.11.5 The precision statement was determined through sta-tistical examination of 145 results, from 9 laboratories,
39、on 16materials over nearly 2 years.12. Keywords12.1 acidity; alkalinity; blue stock; Delta pH; pH; pHdifference; Wet Blue; Wet WhiteASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard
40、 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 years andif n
41、ot 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 committee, which
42、 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 19428-2959,Uni
43、ted 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
44、also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 1 pHMaterial AverageAxRepeat-abilityStandardDeviationSrReproduc-ibilityStandardDeviationSRRepeat-abilityLimitrReproduc-ibility LimitRWet Blue 12412 3.54 0.18 0.50Wet Blue 13112 3.35
45、 0.11 0.30Wet Blue 11912 3.55 0.09 0.24Wet Blue 122211 3.45 0.18 0.50Wet Blue 22112 3.47 0.12 0.32Wet Blue 2513 3.60 0.12 0.33Wet Blue 31312 3.58 0.02 0.06Wet Blue 41812 3.68 0.05 0.15Wet Blue 51612 3.67 0.06 0.17Wet Blue 62812 3.43 0.13 0.35Wet Blue 81512 3.54 0.09 0.24Wet Blue 92412 3.70 0.07 0.18Wet Blue 41313 3.55 0.12 0.33Wet Blue 61313 3.60 0.00 0.06 0.01 0.18Wet Blue 8713 3.58 0.03 0.16 0.08 0.46Wet Blue 92513 3.62 0.01 0.13 0.03 0.37Average 3.56 0.01 0.10 0.04 0.29AThe average of the laboratories calculated averages.D6657 163
