ASTM D1293-2012 Standard Test Methods for pH of Water 《水的PH值标准试验方法》.pdf

1、Designation: D1293 12Standard Test Methods forpH of Water1This standard is issued under the fixed designation D1293; 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 indicates the y

2、ear 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.1. Scope1.1 These test methods cover the determination of pH byelectrometric measurement using the glas

3、s electrode as thesensor. Two test methods are given as follows:SectionsTest Method APrecise Laboratory Measurement 8 to 15Test Method BRoutine or Continuous Measurement 16 to 241.2 Test Method A covers the precise measurement of pH inwater utilizing at least two of seven standard reference bufferso

4、lutions for instrument standardization.1.3 Test Method B covers the routine measurement of pH inwater and is especially useful for continuous monitoring. Twobuffers are used to standardize the instrument under controlledparameters, but the conditions are somewhat less restrictivethan those in Test M

5、ethodA. For on-line measurement, also seeTest Method D6569 which provides more detail.1.4 Both test methods are based on the pH scale establishedby NIST (formerly NBS) Standard Reference Materials.21.5 Neither test method is considered to be adequate formeasurement of pH in water whose conductivity

6、is less thanabout 5 S/cm. Refer to Test Methods D5128 and D5464.1.6 Precision and bias data were obtained using buffersolutions only. It is the users responsibility to assure thevalidity of these test methods for untested types of water.1.7 The values stated in SI units are to be regarded asstandard

7、. No other units of measurement are included in thisstandard.1.8 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-

8、bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D1066 Practice for Sampling SteamD1067 Test Methods for Acidity or Alkalinity of WaterD1129 Terminology Relating to Water4D1192 Guide for Equipment for Sampling Water and Steamin Closed Conduits5D1193 Specificat

9、ion for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD5128 Test Method for On-Line pH Measurement of Waterof Low ConductivityD5464 Test Method for pH Measurement of Water

10、of LowConductivityD6569 Test Method for On-Line Measurement of pHE70 Test Method for pH of Aqueous Solutions With theGlass Electrode3. Terminology3.1 DefinitionsFor definitions of terms used in these testmethods, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 pH,

11、 nthe negative logarithm of the hydrogen ionactivity in an aqueous solution or the logarithm of thereciprocal of the hydrogen ion activity.3.2.1.1 Discussionthe pH of an aqueous solution is de-rived from E, the electromotive force (emf) of the cellglass electrode | solution | reference electrode1The

12、se test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibility of Subcommittee D19.03 on Sampling Waterand Water-Formed Deposits, Analysis of Water for Power Generation and ProcessUse, On-Line Water Analysis, and Surveillance of Water.Current edition appro

13、ved Jan. 1, 2012. Published January 2012. Originallyapproved in 1953. Last previous edition approved in 2005 as D1293 99(2005).DOI: 10.1520/D1293-11.2“Standard Reference Materials: Standardization of pH Measurements” Wu andKoch, NBS Special Publications No. 260-53, 1988.3For referenced ASTM standard

14、s, 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.4Withdrawn.5Withdrawn. The last approved version of this historical standard is referenced

15、on www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.(where the double vertical line represents a liquid junction)when the electrodes are immersed in the solution in thediagrammed position, and Esis the electromotive force

16、 ob-tained when the electrodes are immersed in a reference buffersolution.With the assigned pH of the reference buffer designated aspHs, and E and Esexpressed in volts is the following:6pH 5 pHs1E 2 Es!F2.3026 RTwhere:F = Faraday constant,R = gas constant, andT = absolute temperature, t (C) + 273.15

17、.The reciprocal of F/2.3026 RT is known as the slope of theelectrode, and is the expected difference in observed voltagefor two measurements one pH unit apart. Values of the slope atvarious temperatures are given in Table 1.4. Summary of Test Method4.1 The pH meter and associated electrodes are stan

18、dardizedagainst at least two reference buffer solutions that closelybracket the anticipated sample pH. The sample measurement ismade under strictly controlled conditions and prescribed tech-niques.5. Significance and Use5.1 The pH of water is a critical parameter affecting thesolubility of trace min

19、erals, the ability of the water to formscale or to cause metallic corrosion, and the suitability of thewater to sustain living organisms. It is a defined scale, based ona system of buffer solutions2with assigned values. In purewater at 25C, pH 7.0 is the neutral point, but this varies withtemperatur

20、e and the ionic strength of the sample.7Pure waterin equilibrium with air has a pH of about 5.5, and most naturaluncontaminated waters range between pH 6 and pH 9.6. Purity of Reagents6.1 Reagent grade chemicals shall be used in all tests,except as specifically noted for preparation of reference buf

21、fersolutions. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications are available.8Other grades may beused, provided it is first ascertained that the reagent is

22、 ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D1193, Type I.7. Sampling7.1 Collect samples in accordance with Prac

23、tice D1066,orPractices D3370, whichever is applicable.TEST METHOD APRECISE LABORATORYMEASUREMENT OF pH8. Scope8.1 This test method covers the precise measurement of pHin water under strictly controlled laboratory conditions.9. Interferences9.1 The glass electrode reliably measures pH in nearly allaq

24、ueous solutions and in general is not subject to solutioninterference from color, turbidity, colloidal matter, oxidants, orreductants.9.2 The reference electrode may be subject to interferencesand should be chosen to conform to all requirements ofSections 10 and 12. Refer also to Appendix X1.3.9.3 T

25、he true pH of an aqueous solution or extract is affectedby the temperature. The electromotive force between the glassand the reference electrode is a function of temperature as wellas pH. The temperature effect can be compensated automati-cally in many instruments or can be manually compensated inmo

26、st other instruments. The temperature compensation cor-rects for the effect of changes in electrode slope with tempera-ture but does not correct for temperature effects on thechemical system being monitored. It does not adjust themeasured pH to a common temperature; therefore, the tem-perature shoul

27、d be reported for each pH measurement. Tem-perature effects are discussed further in Appendix X1.2.6Bates, R. G., Determination of pH: Theory and Practice, 2nd Ed., J. Wiley andSons, New York, 1973, p. 29.7The relative acidity or alkalinity measured by pH should not be confused withtotal alkalinity

28、or total acidity (for example, Test Methods D1067). Thus, 0.1 M HCland 0.1 M acetic acid have the same total acidity, but the HCl solution will be moreacidic (approximately pH 1 versus pH 3.).8Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For

29、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. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.TABLE 1 Slope Factor at

30、Various TemperaturesTemperature, C Slope, millivolts0 54.205 55.1910 56.1815 57.1720 58.1725 59.1630 60.1535 61.1440 62.1345 63.1350 64.1255 65.1160 66.1065 67.0970 68.0975 69.0880 70.0785 71.0690 72.0595 73.05D1293 1229.4 The pH response of the glass electrode/reference elec-trode pair is imperfect

31、 at both ends of the pH scale. Theindicated pH value of highly alkaline solutions may be too low,by as much as 1 pH, depending on electrode composition andsample conditions. See X1.5.1. The indicated pH value ofstrong aqueous solutions of salts and strong acids having a pHless than 1, will often be

32、higher than the true pH value.Interferences can be minimized by the selection of the properglass and reference electrodes for measurements in highlyalkaline or acidic solutions.9.5 A few substances sometimes dispersed in water appearto poison the glass electrode. A discussion of this subject isgiven

33、 in Appendix X1.4.10. Apparatus10.1 Laboratory pH MeterAlmost all commercially avail-able meters are of the digital type and will have either manualor automatic calibration, and either manual or automatictemperature (slope) correction. All four types are permissible.However, readability to 0.01 pH i

34、s essential (Section 14), andthe ability to read in millivolts is useful in troubleshooting.10.2 Glass ElectrodeThe pH response of the glass elec-trode shall conform to the requirements set forth in 12.1through 12.6. The glass electrode lead wire shall be shielded.New glass electrodes and those that

35、 have been stored dry shallbe conditioned and maintained as recommended by the manu-facturer.10.3 Reference ElectrodeThis may be used as separate“half cell,” or it may be purchased integral with the glass pHelectrode body, as a combination electrode. The internalreference element may be calomel (mer

36、cury/mercurous chlo-ride), silver/silver chloride, or an iodide-iodine redox couple.For best performance, the reference element should be thesame type in both the reference electrode and inside the pHelectrode. For all three types, the junction between the refer-ence filling solution and the sample

37、may be either a flowing ornonflowing junction. The flowing liquid junction-type unitensures that a fresh liquid junction is formed for each mea-surement and shall be used for Test Method A determinations.If a saturated calomel electrode is used, some potassiumchloride crystals shall be contained in

38、the saturated potassiumchloride solution. If the reference electrode is of the flowingjunction type, the design of the electrode shall permit a freshliquid junction to be formed between the reference electrodesolution and the buffer standard or tested water for eachmeasurement and shall allow traces

39、 of solution to be washedfrom the outer surfaces of the electrodes. To ensure the desiredslow outward flow of reference electrode solution, the solutionpressure inside the liquid junction should be kept somewhat inexcess of that outside the junction. In nonpressurized applica-tions, this requirement

40、 can be met by maintaining the insidesolution level higher than the outside water level. If thereference electrode is of the nonflowing junction type, theseoutward flow and pressurization considerations do not apply.The reference electrode and junction shall perform satisfacto-rily as required in th

41、e standardizing procedure described in12.1 through 12.6.Adiscussion of reference electrodes is givenin Appendix X1.3.10.4 Temperature CompensatorThe thermocompensatoris a temperature-sensitive resistance element immersed in thewater sample with the electrodes. The thermocompensator maybe incorporate

42、d into the pH electrode or may be a separateprobe. The thermocompensator automatically corrects for thechange in slope of the glass electrode (with change oftemperature) but does not correct for actual changes in samplepH with temperature. The automatic thermocompensator is notrequired if the water

43、temperature is essentially constant and theanalyst chooses to use the manual temperature compensationfeature of the pH meter.11. Reagents11.1 Reference Buffer SolutionsThe approximate pH val-ues of the reference buffer solutions measured at severaltemperatures are listed in Table 2. If traceability

44、to NISTstandard reference materials (SRMs) is required, follow ex-actly the NIST certificate drying, preparation, and storageinstructions for the given renewal of the respective SRMbuffer, and obtain the certified value from the certificate for thatSRM renewal at the applicable temperature. The curr

45、entrenewal of each NIST SRM should be used. Buffer solutioncompositions and preparations given in Sections 11.1.1through 11.1.7 are for use with non-NIST materials. For NISTSRMs, follow the instructions included with the SRM.Table 3 identifies each buffer salt by its National Institute ofStandards a

46、nd Technology (NIST) number Dry the buffer saltbefore use. The drying procedure will be according to thecurrent renewal of the NIST certificate. Recommended dryingprocedures for non-NIST reference materials are also provided,in the last column of the table. Keep the five reference buffersolutions wi

47、th pH less than 9.5 in bottles of chemicallyresistant glass. Keep the calcium hydroxide solutions in aplastic bottle that is nonporous to air (that is, polypropylene orhigh density polyethylene). Keep all the reference buffersolutions well-stoppered and replace if a visible change isobserved.11.1.1

48、Borax Reference Buffer Solution (pHs= 9.18 at25C)When using the NIST SRM, prepare in accordancewith the current renewal of the certificate. For other referencematerials, follow associated instructions or dissolve 3.80 g ofsodium tetraborate decahydrate (Na2B4O710H2O) in waterand dilute to 1 L.11.1.2

49、 Calcium Hydroxide Reference Buffer Solution (pHs=12.45 at 25C)When using the NIST SRM, prepare inaccordance with the current renewal of the certificate. For otherreference materials, follow associated instructions or preparepure calcium hydroxide (Ca(OH)2) from well-washed calciumcarbonate (CaCO3) of low-alkali grade by slowly heating thecarbonate in a platinum dish at 1000C and calcining for atleast 45 min at that temperature. After cooling in a dessicator,add the calcined product slowly to water with stirring, heat theresultant suspension to boiling, cool