1、Designation: D 5464 07Standard Test Method forpH Measurement of Water of Low Conductivity1This standard is issued under the fixed designation D 5464; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numb
2、er in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is applicable to determine the pH ofwater samples with a conductivity of 2 to 100 S/cm over thepH range of 3 to 11. pH me
3、asurements of water of lowconductivity are problematic. Specifically, this test methodavoids contamination of the sample with atmospheric gasesand prevents volatile components of the sample from escaping.This test method provides for pH electrodes and apparatus thataddress additional considerations
4、discussed in Annex A2. Thistest method also minimizes problems associated with thesamples pH temperature coefficient when the operator usesthis test method to calibrate an on-line pH monitor or controller(see Appendix X1).1.2 This test method covers the measurement of pH in waterof low conductivity
5、with a lower limit of 2.0 S/cm, utilizinga static grab-sample procedure where it is not practicable totake a real-time flowing sample.NOTE 1Test Method D 5128 for on-line measurement is preferredover this method whenever possible. Test Method D 5128 is not subject tothe limited conductivity range, t
6、emperature interferences, potential KClcontamination, and time limitations found with this method.1.3 For on-line measurements in water with conductivity of100 S/cm and higher, see Test Method D 6569.1.4 For laboratory measurements in water with conductivityof 100 S/cm and higher, see Test Method D
7、1193.1.5 The values stated in SI units are to be regarded asstandard.1.6 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
8、applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 1293 Test Methods for pH of WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee
9、 D19 on WaterD 4453 Practice for Handling of Ultra-Pure Water SamplesD 5128 Test Method for On-Line pH Measurement of Waterof Low ConductivityD 6569 Test Method for On-Line Measurement of pH3. Terminology3.1 DefinitionsFor definitions of terms used in these testmethods, refer to Terminology D 1129.3
10、.2 Definitions of Terms Specific to This Standard:3.2.1 liquid junction potentiala dc potential which ap-pears at the point of contact between the reference electrodessalt bridge (also known as reference junction or diaphragm)and the sample solution. Ideally this potential is near zero, andis stable
11、. However, in low conductivity water it may changefrom its value in buffer solution by an unknown amount, and isa zero offset (1).34. Reagents4.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specificat
12、ions of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.4Other grades may be used,1These test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibility of Subcommittee D19.03 on Sampling Waterand Wat
13、er-Formed Deposits, Analysis of Water for Power Generation and ProcessUse, On-Line Water Analysis, and Surveillance of Water.Current edition approved Aug. 1, 2007. Published August 2007. Originallyapproved in 1993. Last previous edition approved in 2001 as D 5464 93 (2001).2For referenced ASTM stand
14、ards, 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.3The boldface numbers in parentheses refer to the list of references at the end ofthis
15、standard.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For 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 P
16、harmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its
17、 use without lessening the accuracy ofthe determination.4.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water as definedby Type III of Specification D 1193.4.3 Commercial Buffer SolutionsCommercially availableprepared buffers traceable to NIST st
18、andards should be ad-equate to perform the calibration procedures in 10.1-10.4. Theexact pH of the buffer will change with temperature and thispH versus temperature data will be provided by the purveyor ofthe specific buffer. Refer to Test Methods D 1293 for thepreparation of reference buffer soluti
19、ons if desired.4.4 Buffer ACommercially available 7.0 pH buffer.4.5 Buffer BCommercially available 4.0 pH buffer.4.6 Buffer CCommercially available 9.0 or 10.0 pHbuffer.5. Summary of Test Method5.1 The pH meter and associated electrodes are first stan-dardized with two calibration pH buffer solution
20、s.5.2 A grab sample of high purity water is taken by means ofrinsing and filling two narrow mouth bottles at the samplepoint. Once each container is filled to the top with a represen-tative sample excluding any air, the container is capped and thesamples are transported quickly to a laboratory for a
21、nalysis.5.3 pH measurement of the sample is made with high puritywater pH calibration apparatus comprised of pH and referenceelectrodes, and automatic temperature compensator (if used).The first container is used to rinse the sensors and begintemperature equilibration and the second container is use
22、d formeasurement.5.4 A trace amount of KCl electrolyte enters calibrationbuffer solutions and samples via the controlled leakage rate ofthe reference electrode liquid junction (diaphragm) to stabilizethe liquid junction potential. Excessive KCl introduction fromthe electrode liquid junction into low
23、 ionic strength sampleswill increase solution conductivity, and may alter solution pH,and should be avoided.5.5 Temperature must be measured and both Solution Tem-perature Coefficient (STC) and Nernstian electrode effectscompensated, either manually to the measured value or auto-matically by the pH
24、meter. See Appendix X1 for a discussionof temperature effects.6. Significance and Use6.1 pH measurement of low conductivity water is frequentlyapplied to power plant water and condensed steam samples forcorrosion and scale prevention. It is sometimes used in purewater treatment systems between multi
25、ple pass membranes tooptimize performance.6.2 High purity water is highly unbuffered and smallamounts of contamination can change the pH significantly.Specifically, high purity water rapidly absorbs CO2gas fromthe atmosphere, which lowers the pH of the sample. Thesample container and accompanying pH
26、 measurement tech-nique minimize exposure of the high purity water sample to theatmosphere.6.3 The high purity water sample may contain volatile tracecomponents that will dissipate from the sample if exposed tothe atmosphere. The sample container used in this test methodwill prevent these losses.6.4
27、 High purity water has a significant solution temperaturecoefficient. For greatest accuracy the sample to be measuredshould be close to the temperature of the sample stream andappropriate compensation should be applied.6.5 When the preferred Test Method D 5128, which requiresa real-time, flowing sam
28、ple, cannot be utilized for practicalreasons such as physical plant layout, unacceptable loss ofwater, location of on-line equipment sample points, or avail-ability of dedicated test equipment, this method offers a viablealternative. The most significant difference between the twotest methods is tha
29、t Test Method D 5128 obtains a real-time pHmeasurement from a flowing sample and this method obtains atime delayed pH measurement from a static grab sample.6.6 pH measurements of low conductivity water are alwayssubject to interferences (7.1-7.5) and Test Method D 5128 ismore effective in eliminatin
30、g these interferences especiallywith regard to contamination. This static grab sample methodis more prone to contamination and temperature-induced errorsbecause of the time lag between the sampling in the plant andsample pH reading which is taken in the laboratory.7. Interferences7.1 High purity, lo
31、w conductivity samples are especiallysensitive to contamination from atmospheric gases, fromsample containers, from sample handling techniques and fromexcessive electrolyte (KCl) contamination from reference elec-trode or sample preparation such as a KCl “dosing” technique.Refer to Practice D 4453 a
32、nd ASTM STP 823 (2) for discus-sions of sample handling and avoidance of sample contamina-tion.7.2 High purity water will rapidly absorb CO2from theatmosphere and this will lower the pH of the sample at a ratedepending on the buffer capacity of the sample, the surfacearea of the sample exposed to ai
33、r, movement of the sample, andthe concentration of CO2at the surface of the sample whichmay increase if the operator exhales over the container duringsampling or measurement. See Appendix X3, Table X3.1, andFig. X3.1.7.3 The temperature stability of the sample and how closelythe samples temperature
34、matches the sample streams tem-perature will have a direct effect on accuracy of the pHdetermination since temperature compensation is not perfect.7.4 If pH is to be referenced to 25C as required by mostspecifications, temperature compensation must be provided forboth the Nernstian response of the e
35、lectrode output (providedin most pH meters) and solution ionization effects (providedonly with some on-line pH meters or by calculation with labmeters). For a discussion of temperature effects on pH mea-surements of high purity water see Appendix X1.7.5 The reference junction potential can vary with
36、 ionicstrength of the sample and provide an undetectable zero offsetbetween the high ionic strength of the buffer solution and thelow ionic strength of the sample. A flowing junction referenceD 5464 072electrode (one which requires periodic refilling with electrolytesolution or that has internal ele
37、ctrolyte pressurization or both)minimizes this effect.8. Apparatus8.1 pH MeterSee 10.1 in Test Methods D 1293.8.2 Sample ContainersTwo clean, narrow-mouth 250 to500 mL bottles with cap are required. The mouth diametershould be the minimum necessary to allow insertion of theelectrode(s), and temperat
38、ure compensator or thermometer. A3-hole stopper may be used to hold these sensors. Thecontainer and cap minimize exposure to atmospheric gases.8.3 Combination pH ElectrodeA probe incorporating themeasuring, reference and temperature compensator functionsin a single unit is recommended for its ease o
39、f insertion into avery narrow mouth sample container. Each function shouldconform to the characteristics in 8.4-8.6. Where this is notavailable, individual electrodes and compensator (8.4-8.6) maybe used with a 3-hole stopper to hold them and seal thecontainer during measurement.8.4 pH Glass Electro
40、deThe pH response of the glasselectrode shall conform to the requirements set forth in 12.1through 12.5 of Test Methods D 1293. New glass electrodesand those that have been stored dry shall be conditioned andmaintained as recommended by the manufacturer.8.5 Reference ElectrodeDouble junction design,
41、 having aflowing junction with a positive electrolyte leakage rate not toexceed 10 L/h. Prepare and maintain the reference electrodeaccording to the manufacturers instructions.8.6 Temperature CompensatorSee paragraph 10.4 in TestMethods D 1293. The automatic temperature compensatormust adapt for use
42、 with the sample container to measure thetemperature of the water within the container.8.7 Temperature IndicatorA direct temperature indicatingdevice must be used to measure sample water temperaturewithin the sample container if an automatic temperaturecompensator is not used.9. Sampling and Sample
43、Handling9.1 Equipment described in Section 8 should be dedicatedfor high purity water use only.9.2 The sample containers should be rinsed three timesbefore use, with sample or reagent water. The electrode(s) andtemperature device should be rinsed three times, using thesame procedure as with the samp
44、le containers after eachcalibration in pH buffer solutions and before they are insertedinto the first sample container.9.3 Static grab samples are taken via vinyl tubing attachedto the sample take-off point. The other end of the tubing isinserted to the bottom of the sample container. The sampleflow
45、s through the vinyl tube, into the bottom of the container,and then over the top to trough or sink drain. After a 5-minflush of the container with the sample water, the tubing isremoved and the cap immediately installed, excluding any air.This seals the container and isolates the sample from theatmo
46、sphere. The second container is filled and capped in thesame way. In the lab, the first container is used to rinse theelectrodes and temperature device and the second container isused for measurement.10. Calibration10.1 Turn on the pH meter and allow it to warm upaccording to the manufacturers instr
47、uctions.10.2 Remove the electrode(s) and temperature compensator(if used) from storage. Check the reference electrode for properelectrolyte level as recommended by the manufacturer.10.3 Calibrate the electrode(s) and pH meter at two pointsaccording to manufacturers instructions. Also, refer to Secti
48、on12 of Test Methods D 1293 for guidelines on the calibration ofa pH meter and electrode assembly. Use a quiescent sample ofBuffer A and Buffer B if the sample point of interest is below7.0 pH. Use a quiescent sample of Buffer A and Buffer C if thesample point of interest is above 7.0 pH. Use labora
49、toryglassware dedicated for this service only. Thoroughly rinse theelectrode(s) and glassware with reagent water three timesbetween immersion in each buffer solution.10.4 Obtain calibration precision of the pH electrode(s) andthe pH meter by repeating the two-point calibration describedin 10.3, making any necessary readjustments to the pH meter.If the electrode slope (efficiency) is less than 94 % or greaterthan 101 %, refer to manufacturers instructions for repair orreplacement of electrode(s).NOTE 2The pH electrodes in use may pass the above calibrati
