1、Designation:D829421Standard Practice forEstimating pH to Verify Status of Aqueous Samples1This standard is issued under the fixed designation D8294;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
2、 parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice provides information on verifying the pHof aqueous samples before analysis.This practice is notintended to be used for non-aqueous sam
3、ples like oil or grease.1.2 This practice may also be used in adjusting pH ofsamples during various analytical steps.1.3 Wide-range pH papers/strips are used for a rapid indi-cation of pH to within about 1 pH unit,and narrow-range pHpapers/strips are used to indicate pH within about 0.5 pH units.1.4
4、 In some instances,a universal liquid indicator may beused.1.5 UnitsThe values stated in SI units are to be regardedas standard.No other units of measurement are included in thisstandard.1.6 This practice offers a set of instructions for performingone or more specific operations.This document cannot
5、 replaceeducation or experience and should be used in conjunction withprofessional judgment.Not all aspects of this practice may beapplicable in all circumstances.This ASTM Internationalstandard is not intended to represent or replace the standard ofcare by which the adequacy of a given professional
6、 servicemust be judged,nor should this document be applied withoutconsideration of a projects many unique aspects.The word“Standard”in the title means only that the document has beenapproved through the ASTM consensus process.1.7 This standard does not purport to address all of thesafety concerns,if
7、 any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.8 This international standard was developed in accor-dance with internationa
8、lly recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D1293 Test Metho
9、ds for pH of Water3.Terminology3.1 Definitions:3.1.1 pH paper,npieces of paper usually supplied as smallrolls that change color depending on the pH.3.1.1.1 DiscussionpH paper is an inexpensive,robust,andrelatively accurate way of estimating the pH of an aqueousliquid.A strip of filter paper is soake
10、d with different pHindicators,or a mixture of indicators(universal indicator),andallowed to dry.Touching solution to the paper or dipping thepaper in an aliquot of solution causes the color of the indicatoron the paper to change according to the pH.The color andrelative intensity of the color is com
11、pared to a chart from whichpH is estimated.Using only one indicator per paper enables abetter estimate of a narrow pH range.3.1.2 pH paper/strip,nthroughout this practice,the termis used as a reference to both,pH paper and pH strip.3.1.3 pH strips,nstrips of plastic with one or moresquares or rectan
12、gles of pH paper fastened to one end.3.1.3.1 DiscussionpH strips are more rugged than pHpaper.They consist of one or more(usually up to four)smallsquares or rectangles of pH paper attached to one end that aredipped into an aliquot of the sample.In contrast to indicatorpapers described in 3.1.1,pH st
13、rips typically have the indicatorchemically bound or fixed to the paper to prevent it fromleaching into the sample.However,products that containimpregnated filter papers on test strips are also available andthese may release indicator into the sample.When necessary,the type can be checked by putting
14、 a test strip“face down”onabsorbent paper.Each square features a different pH indicatorresulting in different colors and intensity in relation to the pH.The color and intensity of each square is compared to a chartfrom which pH is estimated.The different indicators/colors ofeach square provide users
15、 with greater confidence in theirestimation of the pH.1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.05 on Inorganic Constituents inWater.Current edition approved Oct.1,2021.Published November 2021.DOI:10.1520/D8294-21.2For
16、 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 website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles fo