ASTM D1293-1999(2005) Standard Test Methods for pH of Water《水pH值的标准测试方法》.pdf

1、Designation: D 1293 99 (Reapproved 2005)Standard Test Methods forpH of Water1This standard is issued under the fixed designation D 1293; 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 parenth

2、eses indicates the year of last reapproval. Asuperscript epsilon (e) 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 measu

3、rement using the glass 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 standa

4、rd reference buffersolutions 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 restrictiv

5、ethan those in Test Method A.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 is less thanabout 5 S/cm. Refer to Test Methods D 5128 an

6、d D 5464.1.6 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 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theres

7、ponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D 1066 Practice for Sampling SteamD 1067 Test Methods for Acidity or Alkalinity of WaterD

8、1129 Terminology Relating to WaterD 1192 Specification for Equipment for Sampling Waterand Steam in Closed Conduits4D 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Clo

9、sed ConduitsD 5128 Test Method for On-Line pH Measurement of Waterof Low ConductivityD 5464 Test Methods for pH Measurement of Water of LowConductivityE70Test Method for pH of Aqueous Solutions with theGlass Electrode3. Terminology3.1 DefinitionsFor definitions of terms used in these testmethods, re

10、fer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 pH, nthe pH of an aqueous solution is derived fromE, the electromotive force (emf) of the cellglass electrode | solution | reference electrode(where the double vertical line represents a liquid junction)when the elect

11、rodes are immersed in the solution in thediagrammed position, and Esis the electromotive force 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:5pH 5 pHs1E 2 Es!F2.3

12、026 RTwhere:F = Faraday,R = gas constant, andT = absolute temperature, t (C) + 273.15.The reciprocal of F/2.3026 RT is known as the slope of theelectrode, and is the expected difference in observed voltage1These test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct

13、 responsibility of Subcommittee D19.03 on Sampling ofWater and Water-Formed Deposits, Analysis of Water for Power Generation andProcess Use, On-Line Water Analysis, and Surveillance of Water.Current edition approved Jan. 1, 2005. Published January 2005. Originallyapproved in 1953. Last previous edit

14、ion approved in 1999 as D 1293 99.2“Standard Reference Materials: Standardization of pH Measurements” Wu andKoch, NBS Special Publications No. 260-53, 1988.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AST

15、MStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Withdrawn.5Bates, R. G., Determination of pH: Theory and Practice, 2nd Ed., J. Wiley andSons, New York, 1973, p. 29.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA

16、 19428-2959, United States.for 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 standardizedagainst two reference buffer solutions that closely bracket theanticipated sample pH.

17、 The sample measurement is madeunder strictly controlled conditions and prescribed techniques.5. Significance and Use5.1 The pH of water is a critical parameter affecting thesolubility of trace minerals, the ability of the water to formscale or to cause metallic corrosion, and the suitability of the

18、water 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 withtemperature and the ionic strength of the sample.6Pure waterin equilibrium with air has a pH of about 5.5, and mo

19、st 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 buffersolutions. Unless otherwise indicated, it is intended that allreagents shall conform to the specific

20、ations of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications are available.7Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.6.2 Pu

21、rity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193, Type I.7. Sampling7.1 Collect samples in accordance with Practice D 1066,Specification D 1192, or Practices D 3370, whichever is appli-cable.TEST METHOD APRECISE L

22、ABORATORYMEASUREMENT 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 allaqueous solutions and in general is not subject to solutioninterference from c

23、olor, 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 The true pH of an aqueous solution or extract is affectedby the temperature.

24、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 inmost other instruments. The temperature compensation cor-rects for the effect

25、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 should be reported for each pH measurement. Tem-perature effects are discussed fu

26、rther in Appendix X1.2.9.4 The pH response of the glass electrode/reference elec-trode pair is imperfect 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 indica

27、ted pH value ofstrong aqueous solutions of salts and strong acids having a pHless than 1, will often be 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 substance

28、s sometimes dispersed in water appearto poison the glass electrode. A discussion of this subject isgiven 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 a

29、utomatictemperature (slope) correction. All four types are permissible.However, readability to 0.01 pH is essential (Section 14), andthe ability to read in millivolts is useful in troubleshooting.6The relative acidity or alkalinity measured by pH should not be confused withtotal alkalinity or total

30、acidity (for example, Test Methods D 1067). 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.).7Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggesti

31、ons 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 Various

32、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 73.05D 1293 99 (2005)210.2 Glass ElectrodeThe pH response of the glass elec-trode shall conform to the

33、requirements set forth in 12.1through 12.5. The glass electrode lead wire shall be shielded.New glass electrodes and those that 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 pu

34、rchased integral with the glass pHelectrode body, as a combination electrode. The internalreference element may be calomel (mercury/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

35、electrode and inside the pHelectrode. For all three types, the junction between the refer-ence filling solution and the sample 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 fo

36、r Test Method A determinations.If a saturated calomel electrode is used, some potassiumchloride crystals shall be contained in 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 fo

37、rmed between the reference electrodesolution and the buffer standard or tested water for eachmeasurement and shall allow traces 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 l

38、iquid junction should be kept somewhat inexcess of that outside the junction. In nonpressurized applica-tions, this requirement 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

39、pressurization considerations do not apply.The reference electrode and junction shall perform satisfacto-rily as required in the standardizing procedure described in12.1 through 12.5.Adiscussion of reference electrodes is givenin Appendix X1.3.10.4 Temperature CompensatorThe thermocompensatoris a te

40、mperature-sensitive resistance element immersed in thewater sample with the electrodes. The thermocompensatorautomatically corrects for the change in slope of the glasselectrode (with change of temperature) but does not correct foractual changes in sample pH with temperature. The automaticthermocomp

41、ensator is not required if the water temperature isessentially constant and the analyst chooses to use the manualtemperature compensation feature of the pH meter.11. Reagents11.1 Reference Buffer SolutionsThe pH values of thereference buffer solutions measured at several temperatures arelisted in Ta

42、ble 2. Table 3 identifies each buffer salt by itsNational Institute of Standards and Technology (NIST) numberand provides a recommended drying procedure prior to use.The current renewal of each NIST standard reference materialshould be used. Keep the five reference buffer solutions withpH less than

43、9.5 in bottles of chemically resistant glass. Keepthe calcium hydroxide solutions in a plastic bottle that isnonporous to air (that is, polypropylene or high densitypolyethylene). Keep all the reference buffer solutions well-stoppered and replace if a visible change is observed.11.1.1 Borax Referenc

44、e Buffer Solution (pHs= 9.18 at25C)Dissolve 3.80 g of sodium tetraborate decahydrate(Na2B4O710H2O) in water and dilute to 1 L.11.1.2 Calcium Hydroxide Reference Buffer Solution (pHs=12.45 at 25C)Prepare pure calcium hydroxide (Ca(OH)2)from well-washed calcium carbonate (CaCO3) of low-alkaligrade by

45、slowly heating the carbonate in a platinum dish at1000C and calcining for at least 45 min at that temperature.After cooling in a dessicator, add the calcined product slowlyTABLE 2 pHsof Reference Buffer SolutionsATemperature,CTetroxalateSolutionTartrateSolutionPhthalateSolutionPhosphateSolutionBorax

46、SolutionSodium BicarbonateSodium CarbonateCalcium HydroxideSolution0 1.67 . 4.00 6.98 9.46 10.32 13.425 1.67 . 4.00 6.95 9.39 10.25 13.2110 1.67 . 4.00 6.92 9.33 10.18 13.0015 1.67 . 4.00 6.90 9.28 10.12 12.8120 1.68 . 4.00 6.88 9.23 10.06 12.6325 1.68 3.56 4.00 6.86 9.18 10.01 12.4530 1.68 3.55 4.0

47、1 6.85 9.14 9.97 12.2935 1.69 3.55 4.02 6.84 9.11 9.93 12.1340 1.69 3.55 4.03 6.84 9.07 9.89 11.9845 1.70 3.55 4.04 6.83 9.04 9.86 11.8450 1.71 3.55 4.06 6.83 9.02 9.83 11.7155 1.72 3.55 4.07 6.83 8.99 . 11.5760 1.72 3.56 4.09 6.84 8.96 . 11.4570 1.74 3.58 4.12 6.85 8.92 . .80 1.77 3.61 4.16 6.86 8.

48、89 . .90 1.79 3.65 4.19 6.88 8.85 . .95 1.81 3.67 4.21 6.89 8.83 . .AFor a discussion of the manner in which these pH values were assigned, see Bates, R. G., “Revised Standard Values for pH Measurements from 0 to 95C,” Journalof Research, NBS, Vol 66A, 1962, p. 179. The reference values were obtaine

49、d without a liquid junction, which has an uncertainty of 60.005. Liquid junction electrode valuesmay have an uncertainty of 60.012, with uncertainty6 0.03 for the tetroxalate and the Ca(OH)2. More recent values have been published in pH Measurement by HelmuthGalster, VCH Publishers, Inc., New York, 1991.D 1293 99 (2005)3to water with stirring, heat the resultant suspension to boiling,cool, and filter through a funnel having a fritted-glass disk ofmedium porosity. Collect the solid from the filter, dry it in anoven at 110C, and crush it to a uniform and fi