1、Designation: D2791 07D2791 13Standard Test Method forOn-line Determination of Sodium in Water1This standard is issued under the fixed designation D2791; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the on-line determination of trace amounts of sodium in water using an ion-selective electrode.1.2 This test me
3、thod is based on on-line application of the sodium ion electrode as reported in the technical literature (1-3).2It is generally applicable over the range of 0.01 to 10 000 g/L.1.3 The analyst should be aware that adequate collaborative data for precision and bias statements as required by Practice D
4、2777are not provided. See Section 16 for details.1.4 The values stated in SI units are to be regarded as standard. The inch-pound units given in parentheses are for informationonly.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the re
5、sponsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use. For specific hazard statements see Section 6.2. Referenced Documents2.1 ASTM Standards:3D1066 Practice for Sampling SteamD1129 Terminol
6、ogy Relating to WaterD1193 Specification for Reagent WaterD1293 Test Methods for pH of WaterD2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on WaterD3864 Guide for On-Line Monitoring Systems for Water AnalysisD3370 Practices for Sampling Water from
7、Closed ConduitsD5540 Practice for Flow Control and Temperature Control for On-Line Water Sampling and Analysis3. Terminology3.1 DefinitionsFor definitions of terms used in this test method, refer to Terminology D1129.4. Significance and Use4.1 Sodium is a pervasive contaminant and it is the first ca
8、tion to break through deionization equipment.This test method allowsmeasurement of micrograms per litre (parts per billion) concentrations of sodium in water to monitor low-sodium water sourcesfor indications of contamination or proper operation. Applications include monitoring makeup systems, conde
9、nsers, condensatepolishers, feedwater, boilerwater, and steam.4.2 This test method is more sensitive and selective than conductivity measurements on high purity samples.1 This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03
10、 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, 2007Jan. 1, 2013. Published February 2007 February 2013. Originally approved in 1969. Last previous edition approved
11、 in 20012007as D2791 93D2791 07.(2001). DOI: 10.1520/D2791-07.10.1520/D2791-13.2 The boldface numbers in parentheses refer to the list of references at the end of this test method.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org.
12、 For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary 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 ma
13、y not be technically possible to adequately depict all changes accurately, ASTM recommends that 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.*A Summary of Changes section appears at th
14、e end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Reagents and Materials5.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall
15、 conform to the specifications of the Committee onAnalytical Reagents of theAmerican Chemical Society.4 In manyinstances, reagent grade chemicals contain higher levels of sodium contamination than are compatible with this test method. It mustbe ascertained that the reagent is of sufficiently high pu
16、rity to permit its use without lessening the accuracy of the determination.5.2 Purity of Water Unless otherwise indicated, references to water shall be understood to mean reagent water conformingto Specification D1193, Type I. In addition, the sodium or potassium content shall not exceed 10 g/L(10 p
17、pb) or 1 % of the lowestconcentration to be determined, whichever is lower.5.2.1 Single-distilled water passed through a mixed bed deionizing unit composed of strong cation and anion resins can producean effluent containing less than 1.0 g/L (1.0 ppb) of sodium. If such water is stored in a closed a
18、lkali metal-free container, suchas one made of polyethylene, TFE-fluorocarbon, or stainless steel, subsequent increases in conductivity, usually due to absorptionof carbon dioxide, will not invalidate its use for this purpose.6. Hazards6.1 pH adjusting reagents are strongly alkaline and volatile. Us
19、e normal eye and skin protection when handling ammonia,ammonium hydroxide, dimethylamine, diisopropylamine, monoethylamine, or morpholine. Extra care is needed in handling thegas-permeable tubing exposed to reagents used with the passive diffusion reagent delivery system. Keep reagents in the openwh
20、erever possible and take necessary precautions to keep them from the respiratory tract in event of a spill or leak. Under certainconditions these reagents can produce an explosive mixture with air. OSHA standards must be followed.7. Sampling7.1 Sample the water for on-line sodium ion measurements in
21、 a flowing stream in accordance with Practice D1066, GuideD3864, Practice D3370 and D5540 as applicable.7.2 Regulate the pressure of samples within the instrument manufacturers requirements.7.3 Regulate the temperature of samples that must be condensed, or cooled, or both, to a level between 15 and
22、40C (59 and104F) or within manufacturers requirements. For highest accuracy, bring the sample temperature close to the temperature of thestandards during calibration.7.4 When sample system plumbing has been newly installed, or has not been carrying process stream water for some time, orhas been open
23、 to the atmosphere, it may take 24 h of purging to bring the sodium content at the receiving end down to the samelevel as the sample point, especially when the process stream is less than 1.0 g/L (1.0 ppb). In the case of lines that are very dirtyor have been subject to biological fouling, pumping a
24、 25 % solution of nitric acid is effective for plastic and stainless lines. About30 line-volumes of acid should be pumped through slowly, followed by the fastest practical purge of process water in the amountof 300 volumes. When using an acid-cleaning procedure, confine the acid to the dirty part of
25、 the system. Under no circumstancesshould the acid enter the measuring instrument.7.5 Adjust the sample flow in accordance with the manufacturers recommendation.7.6 Where speed of response is not critical, sequential sampling of multiple streams may be effected with 3-way solenoid valvesfor sample s
26、election. The 3-way valves allow samples not being measured to continue flowing (to drain) and to be current whenthey are selected.Automatic selection should include an adjustable timing device for typical sampling times near 10 min per point.It is not advisable to sequence sample streams of signifi
27、cantly different concentrations using sequential sampling.8. Summary of Test Method8.1 Sodium ion electrodes provide consistent logarithmic response over many orders of magnitude of concentration using thesame principles as pH electrodes but with different ion selectivity. The electrode signal has a
28、 slope of approximately 59 mV/decadechange in sodium ion concentration at 25C (77F).8.2 Where electrode selectivity and the sodium concentration and pH of the sample require it, this This test method includesprovision for the addition of pH adjusting reagent to suppress hydrogen ion concentration an
29、d assure accurate electrode responseto sodium. The lower limit for accurate measurement without reagent appears to be about 1 g/L(1 ppb) in ammonia-treated powerplant samples (4).8.3 This test method is particularly adaptable to high purity water and is relatively free of interferences (1). The over
30、alloperating cost of this system is considerably less than that of on-line flame photometry, and it is more sensitive than electricalconductivity.4 Reagent Chemicals, American Chemical Society Specifications , American Chemical Society, Washington, DC. For suggestions on the testing of reagents not
31、listed bythe American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.D2791 1328.4 The repeatability of this test method is 65 % of the
32、 reading.9. Interferences9.1 The sodium ion electrode, like all potentiometric electrode measuring systems, is responsive to changes in ion activity andnot true concentration changes (that is, the response is to changes in concentration multiplied by an activity coefficient). However,as concentratio
33、ns approach infinite dilution, activity coefficients approach unity and ion concentration and active ion concentrationbecome very nearly equal.9.2 The activity coefficient of sodium ion will vary with changes in the total ionic strength of the solution. Therefore, it isimportant to maintain either a
34、 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 delivered directly to the sample, must not be significant compared with thelowest concentration being measured. Any air contact
35、ing the sample must be sodium-free.9.4 The sodium ion electrode is responsive to certain other monovalent cations. Interference by silver, lithium, hydrogen,potassium, ammonium, and other ions must be considered. The selectivity to interfering ions varies by electrode manufacturer. Inthe low-solids
36、water to which this test method applies, silver and lithium ions are usually absent. Potassium ion, often contributedto the sample by the reference electrode, must be carried downstream away from the sodium ion electrode.Ammonium ion, presentin many power plant samples, generally does not interfere
37、with measurements greater than 1 g/L (1 ppb). Measurements below1 g/L use a stronger base reagent that suppresses the ionization of ammonia.9.5 Elevation of pH so that hydrogen ion concentration is 3 to 4 orders of magnitude lower than that for sodium generally makesthe electrode response independen
38、t of variations in hydrogen ion concentration. concentration of the original sample. Any of thereagents mentioned is satisfactory to increase the pH to a level such that the electrode is essentially insensitive to hydrogen ion,within sodium ranges specified by the manufacturer. Exceptional electrode
39、 selectivity allows some measurements in ammoniatedpower plant samples greater than 1 g/L (1 ppb) sodium without further reagent addition.The apparatus for sodium measurementmay include pH measurement of the conditioned sample to assure absence of this interference.9.6 When this test method is used
40、without pH adjusting reagent, the sample pH and sodium concentration must be within themanufacturers guidelines for the particular sodium electrode to assure accurate measurement.9.6 The sodium ion electrode is not subject to interference from color, turbidity, colloidal matter, oxidants, and reduct
41、ants.10. Apparatus10.1 Measuring InstrumentUse commercially available potentiometric specific ion monitors that have expanded-scaleoperation with adjustable ranges calibrated directly in sodium ion concentration units of micrograms per litre (parts per billion).Electrical output signals must be isol
42、ated from ground and from electrode input and may be scaled for logarithmic, linear, orbilinear ranges.10.2 Sodium Ion ElectrodeUse a commercially available sodium-sensitive electrode (sodium ion electrode). Becauseelectrode selectivities vary among manufacturers, care must be taken that the electro
43、de, reagent or lack of it, and sample conditionsare compatible (see 9.4, and9.5, and 9.6).10.3 Reference ElectrodeUse a reference electrode compatible with the measuring electrode.10.3.1 When the sodium ion electrode has a silver-silver chloride internal half cell, the reference electrode should bes
44、ilver-silver chloride. When the sodium ion electrode has a calomel internal half cell, the reference electrode should be calomel.Dissimilar reference electrodes may be used provided adequate compensation is made electronically to correct for the differencebetween the measuring electrode and the refe
45、rence electrode. If the reference electrode filling solution is an interference in themeasurement of sodium, then the reference electrode 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 Methods D1293. The electrolyte used in r
46、eference electrodes and allmaintenance shall conform to the manufacturers recommendations. With flowing junction reference electrodes to ensure thedesired slow outward flow of electrolyte, the solution pressure inside the junction shall be kept somewhat higher than that outsidethe junction.10.4 Temp
47、erature CompensationUse an automatic temperature compensator in accordance with the manufacturersrecommendation.10.5 Flow Chamber For best results install the electrodes in a flow chamber and take the measurement on a flowing stream.Use a flow chamber as recommended by the manufacturer. If otherwise
48、, design the flow chamber to minimize interference fromthe reference electrode and construct the chamber of inert materials such as plastic or stainless steel.10.5.1 If a plastic is used, cast or machine from a solid block. Gasket electrodes to prevent in-leakage of air. Protection ofelectrodes shal
49、l be in accordance with the manufacturers recommendations. Connections to the flow chamber must be solutionor earth grounded. No glass or copper is permissible in flow chamber construction.D2791 13310.6 Analyzer FluidicsUnattended automatic calibration may be provided using relays and valves for accurately addingsodium standard solution with timing and sequencing controlled by the measuring instrument.11. Reagents and Materials11.1 pH Adjusting Reagents:11.1.1 Ammonia Gas Commercial anhydrous grade ammonia (NH3) having a minimum purity of 99.9 %. G
