1、Designation: D 2791 07Standard Test Method forOn-line Determination of Sodium in Water1This standard is issued under the fixed designation D 2791; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the on-line determination oftrace amounts of sodium in water using an ion-selectiveelectrode.1.2 This test method is
3、 based on on-line application of thesodium ion electrode as reported in the technical literature(1-3).2It is generally applicable over the range of 0.01 to10 000 g/L.1.3 The analyst should be aware that adequate collaborativedata for precision and bias statements as required by PracticeD 2777 are no
4、t provided. See Section 16 for details.1.4 The values stated in SI units are to be regarded asstandard. The inch-pound units given in parentheses are forinformation only.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility
5、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. For specific hazardstatements see Section 6.2. Referenced Documents2.1 ASTM Standards:3D 1066 Practice for Sampling SteamD 1129 Terminology Rela
6、ting 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 D19 on WaterD 3864 Guide for Continual On-Line Monitoring Systemsfor Water AnalysisD 3370 Practices for Sampling Water
7、from Closed ConduitsD 5540 Practice for Flow Control and Temperature Controlfor On-Line Water Sampling and Analysis3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D 1129.4. Significance and Use4.1 Sodium is a pervasive contaminant and it is the fir
8、stcation to break through deionization equipment. This testmethod allows measurement of micrograms per litre (parts perbillion) concentrations of sodium in water to monitor low-sodium water sources for indications of contamination orproper operation. Applications include monitoring makeupsystems, co
9、ndensers, condensate polishers, feedwater, boiler-water, and steam.4.2 This test method is more sensitive and selective thanconductivity measurements on high purity samples.5. Reagents and Materials5.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, i
10、t is intended thatall reagents shall conform to the specifications of the Commit-tee onAnalytical Reagents of theAmerican Chemical Society.4In many instances, reagent grade chemicals contain higherlevels of sodium contamination than are compatible with thistest method. It must be ascertained that th
11、e reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.5.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193, Type I. In addition, the sodium orpotassium cont
12、ent shall not exceed 10 g/L (10 ppb) or 1 % ofthe lowest concentration to be determined, whichever is lower.5.2.1 Single-distilled water passed through a mixed beddeionizing unit composed of strong cation and anion resins canproduce an effluent containing less than 1.0 g/L (1.0 ppb) of1This test met
13、hod is under the jurisdiction of ASTM Committee D19 on Waterand is 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 Feb. 1, 20
14、07. Published February 2007. Originallyapproved in 1969. Last previous edition approved in 2001 as D 2791 93(2001).2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM C
15、ustomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents
16、 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.1*A Summary of Changes section appears at the end of this stan
17、dard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.sodium. If such water is stored in a closed alkali metal-freecontainer, such as one made of polyethylene, TFE-fluorocarbon, or stainless steel, subsequent increases in con-ductivity
18、, usually due to absorption of carbon dioxide, will notinvalidate its use for this purpose.6. Hazards6.1 pH adjusting reagents are strongly alkaline and volatile.Use normal eye and skin protection when handling ammonia,ammonium hydroxide, dimethylamine, diisopropylamine, mo-noethylamine, or morpholi
19、ne. Extra care is needed in handlingthe gas-permeable tubing exposed to reagents used with thepassive diffusion reagent delivery system. Keep reagents in theopen wherever possible and take necessary precautions to keepthem from the respiratory tract in event of a spill or leak. Undercertain conditio
20、ns these reagents can produce an explosivemixture with air. OSHA standards must be followed.7. Sampling7.1 Sample the water for on-line sodium ion measurementsin a flowing stream in accordance with Practice D 1066, GuideD 3864, Practice D 3370 and D 5540 as applicable.7.2 Regulate the pressure of sa
21、mples within the instrumentmanufacturers requirements.7.3 Regulate the temperature of samples that must becondensed, or cooled, or both, to a level between 15 and 40C(59 and 104F) or within manufacturers requirements. Forhighest accuracy, bring the sample temperature close to thetemperature of the s
22、tandards during calibration.7.4 When sample system plumbing has been newly in-stalled, or has not been carrying process stream water for sometime, or has been open to the atmosphere, it may take 24 h ofpurging to bring the sodium content at the receiving end downto the same level as the sample point
23、, especially when theprocess stream is less than 1.0 g/L (1.0 ppb). In the case oflines that are very dirty or have been subject to biologicalfouling, pumping a 25 % solution of nitric acid is effective forplastic and stainless lines. About 30 line-volumes of acidshould be pumped through slowly, fol
24、lowed by the fastestpractical purge of process water in the amount of 300 volumes.When using an acid-cleaning procedure, confine the acid to thedirty part of the system. Under no circumstances should theacid enter the measuring instrument.7.5 Adjust the sample flow in accordance with the manu-factur
25、ers recommendation.7.6 Where speed of response is not critical, sequentialsampling of multiple streams may be effected with 3-waysolenoid valves for sample selection. The 3-way valves allowsamples not being measured to continue flowing (to drain) andto be current when they are selected. Automatic se
26、lectionshould include an adjustable timing device for typical samplingtimes near 10 min per point. It is not advisable to sequencesample streams of significantly different concentrations usingsequential sampling.8. Summary of Test Method8.1 Sodium ion electrodes provide consistent logarithmicrespons
27、e over many orders of magnitude of concentrationusing the same principles as pH electrodes but with differention selectivity. The electrode signal has a slope of approxi-mately 59 mV/decade change in sodium ion concentration at25C (77F).8.2 Where electrode selectivity and the sodium concentra-tion a
28、nd pH of the sample require it, this test method includesprovision for the addition of pH adjusting reagent to suppresshydrogen ion concentration and assure accurate electroderesponse to sodium. The lower limit for accurate measurementwithout reagent appears to be about 1 g/L (1 ppb) inammonia-treat
29、ed power plant samples (4).8.3 This test method is particularly adaptable to high puritywater and is relatively free of interferences (1). The overalloperating cost of this system is considerably less than that ofon-line flame photometry, and it is more sensitive than electri-cal conductivity.8.4 Th
30、e repeatability of this test method is 65 % of thereading.9. Interferences9.1 The sodium ion electrode, like all potentiometric elec-trode measuring systems, is responsive to changes in ionactivity and not true concentration changes (that is, theresponse is to changes in concentration multiplied by
31、anactivity coefficient). However, as concentrations approachinfinite dilution, activity coefficients approach unity and ionconcentration and active ion concentration become very nearlyequal.9.2 The activity coefficient of sodium ion will vary withchanges in the total ionic strength of the solution.
32、Therefore, itis important to maintain either a low or constant ionic strength.A constant flow of pH adjusting reagent generally establishes aconsistent ionic strength.9.3 The sodium content of pH adjusting reagent, if delivereddirectly to the sample, must not be significant compared withthe lowest c
33、oncentration being measured. Any air contactingthe sample must be sodium-free.9.4 The sodium ion electrode is responsive to certain othermonovalent cations. Interference by silver, lithium, hydrogen,potassium, ammonium, and other ions must be considered. Theselectivity to interfering ions varies by
34、electrode manufacturer.In the low-solids water to which this test method applies, silverand lithium ions are usually absent. Potassium ion, oftencontributed to the sample by the reference electrode, must becarried downstream away from the sodium ion electrode.Ammonium ion, present in many power plan
35、t samples, gener-ally does not interfere with measurements greater than 1 g/L(1 ppb). Measurements below 1 g/L use a stronger basereagent that suppresses the ionization of ammonia.9.5 Elevation of pH so that hydrogen ion concentration is 3to 4 orders of magnitude lower than that for sodium generally
36、makes the electrode response independent of variations inhydrogen ion concentration. Any of the reagents mentioned issatisfactory to increase the pH to a level such that the electrodeis essentially insensitive to hydrogen ion, within sodium rangesspecified by the manufacturer. Exceptional electrode
37、selectivityallows some measurements in ammoniated power plantsamples greater than 1 g/L (1 ppb) sodium without furtherreagent addition.D 2791 0729.6 When this test method is used without pH adjustingreagent, the sample pH and sodium concentration must bewithin the manufacturers guidelines for the pa
38、rticular sodiumelectrode to assure accurate measurement.9.7 The sodium ion electrode is not subject to interferencefrom color, turbidity, colloidal matter, oxidants, and reductants.10. Apparatus10.1 Measuring InstrumentUse commercially availablepotentiometric specific ion monitors that have expanded
39、-scaleoperation with adjustable ranges calibrated directly in sodiumion concentration units of micrograms per litre (parts perbillion). Electrical output signals must be isolated from groundand from electrode input and may be scaled for logarithmic,linear, or bilinear ranges.10.2 Sodium Ion Electrod
40、eUse a commercially availablesodium-sensitive electrode (sodium ion electrode). Becauseelectrode selectivities vary among manufacturers, care must betaken that the electrode, reagent or lack of it, and sampleconditions are compatible (see 9.4, 9.5, and 9.6).10.3 Reference ElectrodeUse a reference el
41、ectrode com-patible with the measuring electrode.10.3.1 When the sodium ion electrode has a silver-silverchloride internal half cell, the reference electrode should besilver-silver chloride. When the sodium ion electrode has acalomel internal half cell, the reference electrode should becalomel. Diss
42、imilar reference electrodes may be used providedadequate compensation is made electronically to correct for thedifference between the measuring electrode and the referenceelectrode. If the reference electrode filling solution is aninterference in the measurement of sodium, then the referenceelectrod
43、e must be downstream from the measuring electrode(see 9.4 and 10.3.2).10.3.2 If calomel electrodes are used, refer to Test MethodsD 1293. The electrolyte used in reference electrodes and allmaintenance shall conform to the manufacturers recommen-dations. With flowing junction reference electrodes to
44、 ensurethe desired slow outward flow of electrolyte, the solutionpressure inside the junction shall be kept somewhat higher thanthat outside the junction.10.4 Temperature CompensationUse an automatic tem-perature compensator in accordance with the manufacturersrecommendation.10.5 Flow ChamberFor bes
45、t results install the electrodesin a flow chamber and take the measurement on a flowingstream. Use a flow chamber as recommended by the manufac-turer. If otherwise, design the flow chamber to minimizeinterference from the reference electrode and construct thechamber of inert materials such as plasti
46、c or stainless steel.10.5.1 If a plastic is used, cast or machine from a solidblock. Gasket electrodes to prevent in-leakage of air. Protectionof electrodes shall be in accordance with the manufacturersrecommendations. Connections to the flow chamber must besolution or earth grounded. No glass or co
47、pper is permissiblein flow chamber construction.11. Reagents and Materials11.1 pH Adjusting Reagents:11.1.1 Ammonia GasCommercial anhydrous grade am-monia (NH3) having a minimum purity of 99.9 %. Gas isabsorbed directly by the sample.11.1.2 Ammonium HydroxideCommercial ammonia solu-tion, approximate
48、ly 29 % NH3in water. Vapor diffuses into thesample through an ion-impermeable membrane.11.1.3 DiisopropylamineCommercial grade liquid is va-porized and transported by an inert carrier gas to the samplestream, or vapor diffuses into the sample through an ion-impermeable membrane.11.1.4 Dimethylamine
49、GasCommercial grade having aminimum purity of 99 %. Gas is absorbed directly by thesample.11.1.5 MonoethylamineCommercial grade vapor diffusesinto the sample through an ion impermeable membrane.11.2 Sodium Chloride Stock Solution (1.00 mL = 0.100 mgNa)Dissolve in water 0.2542 g of sodium chloride (NaCl),dried to constant weight at 105C in water, and dilute to 1 L ina thoroughly cleaned polyethylene flask. Store sodium stock ina polyethylene or equally alkali metal-free container. Preparestandards of lesser concentrations by dilutions of the stocksolu
