ASTM D1293-2018 Standard Test Methods for pH of Water《水的PH值标准试验方法》.pdf

1、Designation: D1293 12D1293 18Standard 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 indicat

2、es the year 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 U.S. Department of Defense.1. Scope1.1 These test methods cover the determination of pH by electrometric measurement

3、using the glass electrode as the sensor.Twotest methods are given as follows:SectionsTest Method APrecise Laboratory Measurement 8 to 15Test Method BRoutine or Continuous Measurement 16 to 24SectionsTest Method APrecise Laboratory Measurement 8 to 15Test Method BRoutine or Continuous Measurement 16

4、to 241.2 Test Method A covers the precise measurement of pH in water utilizing at least two of seven standard reference buffersolutions for instrument standardization.1.3 Test Method B covers the routine measurement of pH in water and is especially useful for continuous monitoring. Twobuffers are us

5、ed to standardize the instrument under controlled parameters, but the conditions are somewhat less restrictive thanthose in Test Method A. For on-line measurement, also see Test Method D6569 which provides more detail.1.4 Both test methods are based on the pH scale established by NIST (formerly NBS)

6、 Standard Reference Materials.21.5 Neither test method is considered to be adequate for measurement of pH in water whose conductivity is less than about 5S/cm. Refer to Test Methods D5128 and D5464.1.6 Precision and bias data were obtained using buffer solutions only. It is the users responsibility

7、to assure the validity of thesetest methods for untested types of water.1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this The valuesgiven in parentheses are mathematical conversions to inch-pound units that are provided for informati

8、on only and are notconsidered standard.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theap

9、plicability of regulatory limitations prior to use.1.9 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby th

10、e World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D1066 Practice for Sampling SteamD1067 Test Methods for Acidity or Alkalinity of WaterD1129 Terminology Relating to Water1 These test methods are under the jurisdiction of ASTM Committee

11、 D19 on Water and are the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.Current edition approved Jan. 1, 2012Jan. 15, 2018. Published January 2012Janua

12、ry 2018. Originally approved in 1953. Last previous edition approved in 20052011 asD1293 99(2005).11. DOI: 10.1520/D1293-11.10.1520/D1293-18.2 “Standard Reference Materials: Standardization of pH Measurements” Wu and Koch, NBS Special Publications No. 260-53, 1988.Wu, and Koch, “Standard ReferenceMa

13、terials: Standardization of pH Measurements,” NBS Special Publications No. 260-53, 1988.3 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 Summar

14、y page on the ASTM website.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. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends t

15、hat 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 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D1192 Guide for Equip

16、ment for Sampling Water and Steam in Closed Conduits (Withdrawn 2003)4D1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD5128 Test Method for On-Line p

17、H Measurement of Water of Low ConductivityD5464 Test Method for pH Measurement of Water of Low ConductivityD6569 Test Method for On-Line Measurement of pHE70 Test Method for pH of Aqueous Solutions With the Glass Electrode3. Terminology3.1 DefinitionsFor definitions of terms used in these test metho

18、ds, refer to Terminology D1129.3.1 Definitions:3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 pH, nthe negative logarithm of the hydrogen ion activity in an aqueous solution or the logarithm of the reciprocal

19、ofthe hydrogen ion activity.3.2.1.1 DiscussiontheThe pH of an aqueous solution is derived from E, the electromotive force (emf) of the cellcell:glass electrode | solution | reference electrode(where the double vertical line represents a liquid junction) when the electrodes are immersed in the soluti

20、on in the dia-grammed position, and Es is the electromotive force obtained when the electrodes are immersed in a reference buffer solution.With the assigned pH of the reference buffer designated as pHs, and E and Es expressed in volts is the following:4pH5pHs1E 2Es!F2.3026 RTwhere:F = Faraday consta

21、nt,R = gas constant, andT = absolute temperature, t(C) + 273.15.The reciprocal of F/2.3026 RT is known as the slope of the electrode, and is the expected difference in observed voltage for twomeasurements one pH unit apart. Values of the slope at various temperatures are given in Table 1.4 Bates, R.

22、 G., Determination of pH: Theory and Practice, 2nd Ed., J. Wiley and Sons, New York, 1973, p. 29.Bates, R. G., Determination of pH: Theory and Practice,2nd ed., J. Wiley and Sons, New York, 1973, p. 29.TABLE 1 Slope Factor at Various TemperaturesTemperature, C Slope, millivolts0 54.205 55.1910 56.18

23、15 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 1824. Summary of Test Method4.1 The pH meter and associated electrodes are standardized against at least two reference buffer solutions that closely bracketth

24、e anticipated sample pH. The sample measurement is made under strictly controlled conditions and prescribed techniques.5. Significance and Use5.1 The pH of water is a critical parameter affecting the solubility of trace minerals, the ability of the water to form scale orto cause metallic corrosion,

25、and the suitability of the water to sustain living organisms. It is a defined scale, based on a system ofbuffer solutions2 with assigned values. In pure water at 25C, pH 7.0 is the neutral point, but this varies with temperature and theionic strength of the sample.5 Pure water in equilibrium with ai

26、r has a pH of about 5.5, and most natural uncontaminated watersrange 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 buffer solutions.Unless otherwise indicated, it is intended that all reage

27、nts shall conform to the specifications of the Committee on AnalyticalReagents of the American Chemical Society, where such specifications are available.6 Other grades may be used, provided it isfirst ascertained that the reagent is of sufficiently high purity to permit its use without lessening the

28、 accuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, references to water that is used for reagent preparation, rinsing, or dilutionshall be understood to mean reagent water conforming to Specification D1193, Type I.7. Sampling7.1 Collect samples in accordance with Practice D

29、1066, or Practices D3370, whichever is applicable.TEST METHOD APRECISE LABORATORY MEASUREMENT OF pH8. Scope8.1 This test method covers the precise measurement of pH in water under strictly controlled laboratory conditions.8. Scope8.1 This test method covers the precise measurement of pH in water und

30、er strictly controlled laboratory conditions.9. Interferences9.1 The glass electrode reliably measures pH in nearly all aqueous solutions and in general is not subject to solution interferencefrom color, turbidity, colloidal matter, oxidants, or reductants.9.2 The reference electrode may be subject

31、to interferences and should be chosen to conform to all requirements of Sections10 and 12. Refer also to Appendix X1.3.9.3 The true pH of an aqueous solution or extract is affected by the temperature. The electromotive force between the glass andthe reference electrode is a function of temperature a

32、s well as pH. The temperature effect can be compensated automatically inmany instruments or can be manually compensated in most other instruments. The temperature compensation corrects for the effectof changes in electrode slope with temperature but does not correct for temperature effects on the ch

33、emical system beingmonitored. It does not adjust the measured pH to a common temperature; therefore, the temperature should be reported for eachpH measurement. Temperature effects are discussed further in Appendix X1.2.9.4 The pH response of the glass electrode/reference electrode pair is imperfect

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

35、ehigher than the true pH value. Interferences can be minimized by the selection of the proper glass and reference electrodes formeasurements in highly alkaline or acidic solutions.9.5 A few substances sometimes dispersed in water appear to poison the glass electrode. A discussion of this subject is

36、givenin Appendix X1.4.5 The relative acidity or alkalinity measured by pH should not be confused with total alkalinity or total acidity (for example, Test Methods D1067). Thus, 0.1 M HCl and0.1 M acetic acid have the same total acidity, but the HCl solution will be more acidic (approximately pH 1 ve

37、rsus pH 3.).3).6 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United

38、 States Pharmacopeia and NationalFormulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.D1293 18310. Apparatus10.1 Laboratory pH MeterAlmost all commercially available meters are of the digital type and will have either manual orautomatic calibration, and either manual or automatic te

39、mperature (slope) correction. All four types are permissible. However,readability to 0.01 pH is essential (Section 14), and the ability to read in millivolts is useful in troubleshooting.10.2 Glass ElectrodeThe pH response of the glass electrode shall conform to the requirements set forth in 12.1 th

40、rough 12.6.The glass electrode lead wire shall be shielded. New glass electrodes and those that have been stored dry shall be conditioned andmaintained as recommended by the manufacturer.10.3 Reference ElectrodeThis may be used as separate “half cell,” or it may be purchased integral with the glass

41、pH electrodebody, as a combination electrode. The internal reference element may be calomel (mercury/mercurous chloride), silver/silverchloride, or an iodide-iodine redox couple. For best performance, the reference element should be the same type in both thereference electrode and inside the pH elec

42、trode. For all three types, the junction between the reference filling solution and thesample may be either a flowing or nonflowing junction. The flowing liquid junction-type unit ensures that a fresh liquid junctionis formed for each measurement and shall be used for Test MethodAdeterminations. If

43、a saturated calomel electrode is used, somepotassium chloride crystals shall be contained in the saturated potassium chloride solution. If the reference electrode is of theflowing junction type, the design of the electrode shall permit a fresh liquid junction to be formed between the reference elect

44、rodesolution and the buffer standard or tested water for each measurement and shall allow traces of solution to be washed from the outersurfaces of the electrodes. To ensure the desired slow outward flow of reference electrode solution, the solution pressure inside theliquid junction should be kept

45、somewhat in excess of that outside the junction. In nonpressurized applications, this requirementcan be met by maintaining the inside solution level higher than the outside water level. If the reference electrode is of thenonflowing junction type, these outward flow and pressurization considerations

46、 do not apply. The reference electrode and junctionshall perform satisfactorily as required in the standardizing procedure described in 12.1 through 12.6. A discussion of referenceelectrodes is given in Appendix X1.3.10.4 Temperature CompensatorThe thermocompensator is a temperature-sensitive resist

47、ance element immersed in the watersample with the electrodes. The thermocompensator may be incorporated into the pH electrode or may be a separate probe. Thethermocompensator automatically corrects for the change in slope of the glass electrode (with change of temperature) but does notcorrect for ac

48、tual changes in sample pH with temperature. The automatic thermocompensator is not required if the watertemperature is essentially constant and the analyst chooses to use the manual temperature compensation feature of the pH meter.11. Reagents11.1 Reference Buffer Solutions SolutionsThe approximate

49、pH values of the reference buffer solutions measured at severaltemperatures are listed in Table 2. If traceability to NIST standard reference materials (SRMs) is required, follow exactly the NISTcertificate drying, preparation, and storage instructions for the given renewal of the respective SRM buffer, and obtain the certifiedvalue from the certificate for that SRM renewal at the applicable temperature. The current renewal of each NIST SRM should beTABLE 2 Approximate pHs of Reference Buffer SolutionsATemperature,CTetroxalateSolutionTartrateSolutionPhthal