1、Designation: D6657 08D6657 14Standard Test Method forpH of Wet Blue1This 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 indic
2、ates 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 of all types of wet blue and wet white.1.2 For pH of wet white, the procedure is identical, substitute wet whi
3、te for wet blue in the standard method.1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof t
4、he user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D6659 Practice for Sampling and Preparation of Wet Blue for Physical and Chemical TestsE177 Practice for Use
5、of the Terms Precision and Bias in ASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study to Determine 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 negative logarithm of the hydrogen i
6、on activity.Asolution of pH 7 is neutralat 24 C. Lower numbers indicate increasing acidity; higher numbers, increasing alkalinity.4. Significance and Use4.1 This test method is designed to measure the pH of a distilled-water extract of wet blue. This is considered to be a measureof the acidity or al
7、kalinity of the wet blue. Excessive acidity or alkalinity may have a deleterious effect on the aging characteristicsof wet blue 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 suita
8、ble electrode. The meter shall have an accuracy of at least 0.01 pH unit and reproducibilityof 0.05 pH unit.5.2 Analytical Balance, sensitive to 0.01 g or greater.6. Reagents6.1 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean distilled water or water ofequa
9、l purity. Distilled water shall have a pH value of not less than 5.5 nor more than 7.0 and shall give a residue of not more than0.5 mg, when 100 mL is evaporated and dried in a platinum dish.6.2 Commercially Standardized pH Solutions3:1 This test method is under the jurisdiction of ASTM Committee D3
10、1 on Leather and is the direct responsibility of Subcommittee D31.02 on Wet Blue.Current edition approved Sept. 1, 2008April 1, 2014. Published October 2008June 2014. Originally approved in 2001. Last previous edition approved in 20062008 asD6657 - 01D6657 - 08.(2006). DOI: 10.1520/D6657-08.10.1520/
11、D6657-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Commercial buffer salts and solutions prepared in
12、accordance with National Bureau of Standards recommendations are sold by reputable laboratory supply houses andmay be used.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becausei
13、t may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr
14、Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.2.1 Alkaline Phosphate Buffer Solution (0.01 M trisodium phosphate, pH = 11.72 at 25 C)Dissolve 1.42 g of anhydrousdisodium hydrogen phosphate (Na2HPO4) in 100 mL of a 0.1 N carbonate-free solution of sodium hydroxide (NaOH
15、) and diluteto 1 L with water.6.2.2 Borax Buffer Solution (0.01 M, pH = 9.18 at 25 C)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 25 C)Add 2 g of concentrated hydrochloric acid (HCl, sp gr 1.19) to 450 g of water.S
16、tandardize and dilute to 0.1 N.6.2.4 Phosphate Buffer Solution (0.025 M with respect to each phosphate, salt pH = 6.86 at 2.5 C)Dissolve 3.40 g ofmonobasic potassium phosphate (KH2PO4) and 3.55 g of anhydrous dibasic sodium phosphate (Na2HPO4) in water and dilute to1 L.6.2.5 Potassium Hydrogen Phtha
17、late Buffer Solution (0.05 M, pH = 4.01 at 25 C)Dissolve 10.21 g of potassium hydrogenphthalate (KHC8H4O4) in water and dilute to 1 L.7. Test Specimen7.1 The specimen shall consist of 10 g, 6 1 g, from a composite sample prepared according to Practice D6659.8. Standardization8.1 Use manufacturers di
18、rections for establishing two point standardization with standard pH solutions that read on either sideof the anticipated pH of the solution to be tested. Wash electrodes by immersing in three changes of water and establish a freshliquid junction after blotting electrodes if using sleeve type electr
19、ode prior to testing each solution.8.2 Check for electrode drift with either of the buffers and restandardize if necessary.9. Procedure9.1 Weigh the specimen to the nearest 0.01 g and transfer to a 250 mL Erlenmeyer flask. Add water in the amount of ten timesthe mass of the specimen. Stopper the fla
20、sk and agitate thoroughly. Let stand at the Standard Laboratory Temperature, 23.0 6 1C (73.4 6 1.8 F), with occasional agitation for not less than 4 nor more than 24 h. Agitate thoroughly and if necessary transferto a clean beaker or decant if possible.9.2 Determine the pH of the wet blue water mixt
21、ure or solution, reading the meter to the closest 0.05 unit.9.3 If a pH difference figure (Delta pH) is desired, remove a 5 ml to 10 ml aliquot of the liquid into a beaker and dilute ten fold.Mix well and determine the pH. Calculate the difference in pH from the initial reading.NOTE 1If the pH diffe
22、rence figure is 0.7 or greater, it is an indication that 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 nearest 0.05 pH unit.10.1.2 The pH difference figure (Delta pH) shall be reported to the nearest 0.05 pH unit.11.
23、Precision and Bias11.1 This test method is adopted from the leather tanning industry where it has long been in use and approved for disseminationas a standard method before the inclusion of precision and bias statements was mandated. The pH of wet blue can changesignificantly over time after removal
24、 from the chrome-tanning vessel. This change happens because chemical reactions involvingthe basicity of the chromium sulfate complex continue to occur within the wet blue. The amount and rate of these pH changes isdependent on the specific processes and materials used to manufacture the wet blue. T
25、he user is cautioned to verify that theprecision and bias (or reproducibility) of this method is adequate for the contemplated application.11.2 The precision of this test method is based on an intralaboratoy study of ASTM WK40322, New Standard Test Method forthe Determination of pH in Wet Blue and W
26、et White, conducted in 2012. Nine laboratories participated in this study, testing 16Wet Blue samples. Every “test result” represents an individual determination. The laboratories were asked to report a single testresult for 13 materials and duplicate test results for 3 materials. Except for the abs
27、ence of replicate test results from all of the studymaterials, Practice E691 was followed for the design and analysis of the data; the details are give in an ASTM research report.411.2.1 Repeatability (r)The difference between repetitive results obtained by the same operator in a given laboratory ap
28、plyingthe same test method with the same apparatus under constant operating conditions on identical test material within short intervalsof time would in the long run, in the normal and correct operation of the test method, exceed the following values only in one casein 20.4 Supporting data have been
29、 filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D31-1021. Contact ASTM CustomerService at serviceastm.org.D6657 14211.2.1.1 Repeatability can be interpreted as maximum difference between two results, obtained under repeatability conditions,that is accep
30、ted as plausible due to random causes under normal and correct operation of the test method.11.2.1.2 Repeatability limits are listed in Table 1.11.2.2 Reproducibility (R)The difference between two single and independent results obtained by different operators applyingthe same test method in differen
31、t laboratories using different apparatus on identical test material would, in the long run, in thenormal and correct operation of the test method, exceed the following values only in one case in 20.11.2.2.1 Reproducibility can be interpreted as maximum difference between two results, obtained under
32、reproducibilityconditions, that is accepted as plausible due to random causes under normal and correct operation of the test method.11.2.2.2 Reproducibility limits are listed in Table 1.11.2.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.11.2
33、.4 Any judgment in accordance with 11.2.1 would normally have an approximate 95 % probability of being correct,however the precision statistics obtained in this ILS must not be treated as exact mathematical quantities which are applicable toall circumstances and uses. The limited number of materials
34、 for which replicate results were reported essentially guarantees thatthere will be times when differences greater than predicted by the ILS results will arise, sometimes with considerably greater orsmaller frequency than the 95 % probability limit would imply. Consider the repeatability limit as a
35、guide, and the associatedprobability of 95 % as only a rough indicator of what can be expected.11.3 BiasNo information can be presented on the bias of the procedure in Test Method D6657 for measuring pH because nomaterial having an accepted reference value was included in the analysis.11.4 The preci
36、sion statement was determined through statistical examination of 145 results, from 9 laboratories, on 16 materialsover nearly 2 years.12. Keywords12.1 acidity; alkalinity; blue stock; Delta pH; pH; pH difference; wet blue; wet whiteASTM International takes no position respecting the validity of any
37、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 revis
38、ion 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 or for additional standardsand should be addressed to ASTM International Headquarters. Your co
39、mments 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 known to the ASTM Committee on Standards, at the address shown below.This standard is copyrigh
40、ted by ASTM International, 100 Barr Harbor Drive, 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
41、-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/).TABLE 1 pHMaterial AverageAxRepeat-abilityStandardDeviationSrReproduc-ibilityStandardDeviationSRRepeat-abilityLimitrReproduc-ibility Limi
42、tRWet Blue 12412 3.54 0.18 0.50Wet Blue 13112 3.35 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 143
