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2、 93 (Reapproved 2001)An American National StandardStandard Test Methods forContinuous 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
3、year of last revision. A number 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 These test methods cover the continuous determination of trace amounts of sodium in water using an ion-selec
4、tive electrode and flame photometry. Two test methods are in- cluded:D 1192 Specification for Equipment and Sampling Waterand Steam in Closed Conduits3D 1193 Specification for Reagent Water3D 1293 Test Methods for pH of Water3D 2777 Practice for Determination of Precision and Bias of3SectionsTest Me
5、thod AIon-Selective Electrode8 to 16Test Method BFlame Photometry17 to 261.2 Test Method A is based on continuous application of the sodium ion electrode as reported in the technical literature(1-3). 2 It is generally applicable over the range of 0.05 to10 000 g/L.1.3 Test Method B is based on the u
6、se of flame photometry.It is most applicable to measurements below 20 g/L. Com- pared with Test Method A, it is less vulnerable to interference from other monovalent cations at low concentrations and can reach equilibrium with very low sample throughput.1.4 The analyst should be aware that adequate
7、collaborative data for precision and bias statements as required by Practice D 2777 are not provided. See Sections 16 and 26 for details.1.5 The values stated in SI units are to be regarded as standard. The inch-pound units given in parentheses are for information only.1.6 This standard does not pur
8、port to address all of the safety concerns, if any, associated with its use. It is the responsibility 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 hazard statements see Secti
9、on 6.2. Referenced Documents2.1 ASTM Standards:D 1066 Practice for Sampling Steam3D 1129 Terminology Relating to Water31 These test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibility of Subcommittee D19.03 on Sampling ofApplicable Methods of Committee
10、D-19 on WaterD 3864 Guide for Continual On-Line Monitoring Systems for Water Analysis33. Terminology3.1 DefinitionsFor definitions of terms used in these test methods, refer to Terminology D 1129.4. Significance and Use4.1 Sodium is a pervasive contaminant and the first cation to break through deion
11、ization equipment. These test methods allow measurements of micrograms per litre (parts per billion) concentrations of sodium in water for monitoring low-sodium water sources for indications of contamination or proper operation. Applications include monitoring of demineralizer system performance and
12、 power plant boiler carryover and condenser leakage.4.2 These test methods are more sensitive and selective than conductivity measurements on high purity samples.5. Reagents and Materials5.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is inten
13、ded that all reagents shall conform to the specifications of the Commit- tee on Analytical Reagents of the American Chemical Society.4In many instances, reagent grade chemicals contain higher levels of sodium contamination than are compatible with these test methods. It must be ascertained that the
14、reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.5.2 Purity of Water Unless otherwise indicated, refer- ences to water shall be understood to mean reagent waterWater and Water-Formed Deposits, Surveillance of Water, and Flow Measurement of
15、Water.Current edition approved April 15, 1993. Published June 1993. Originally published as D 2791 69T. Last previous edition D 2791 87.2 The boldface numbers in parentheses refer to the list of references at the end ofthese test methods.3 Annual Book of ASTM Standards, Vol 11.01.4 Reagent Chemicals
16、, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
17、Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1D 2791 93 (2001)conforming to Specification D 119
18、3, Type I. In addition, thesodium or potassium content shall not exceed 10 g/L (10 ppb) or 1 % of the lowest concentration 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 produce an effluent c
19、ontaining less than 1.0 g/L (1.0 ppb) of 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, usually due to absorption of carbon dioxide, will not invalidate its use f
20、or this purpose.6. Hazards6.1 Test Method A pH adjusting reagents are strongly alkaline and volatile. Use normal eye and skin protection when handling ammonia, ammonium hydroxide, dimethylamine, diisopropylamine, monoethylamine, or morpholine. Extra care is needed in handling the gas-permeable tubin
21、g immersed in liquid reagents used with the passive diffusion reagent delivery system. Keep reagents in the open wherever possible and take necessary precautions to keep them from the respiratory tract in event of a spill or leak. Under certain conditions these reagents can produce an explosive mixt
22、ure with air. OSHA standardsmust be followed.6.2 Test Method B:6.2.1 Use normal safety precautions in handling hydrogen and oxygen gas.6.2.2 Use extreme care to avoid contact of skin with the extremely hot oxy-hydrogen flame as instant third-degree burns would result.6.2.3 For unattended operation o
23、f flame photometer, provide means to ensure that flame gases are shut off quickly and automatically if the flame should be extinguished for any reason.7. Sampling7.1 Sample the water for continuous sodium ion measure- ments in a flowing stream in accordance with Practice D 1066, Specification D 1192
24、, and Guide D 3864, 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 40C(59 and 104F) or within manufacturers requirements. For highest acc
25、uracy, bring the sample temperature close to the temperature of the standards during calibration.7.4 When sample system plumbing has been newly in- stalled, or has not been carrying process stream water for some time, or has been open to the atmosphere, it may take 24 h of purging to bring the sodiu
26、m content at the receiving end down to the same level 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 dirty or have been subject to biological fouling, pumping a 25 % solution of nitric acid is effective for plastic and stain
27、less lines. About 30 line-volumes of acid should be pumped through slowly, followed by the fastest practical 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 me
28、asuring instrument.7.5 Adjust the sample flow in accordance with the manu- facturers recommendation.7.6 Where speed of response is not critical, sequential sampling of multiple streams may be effected with 3-way solenoid valves for sample selection. The 3-way valves allow samples not being measured
29、to continue flowing (to drain) and to be current when they are selected. Automatic selection should include an adjustable timing device for typical sampling times near 10 min per point.TEST METHOD ASODIUM ION ELECTRODE8. Scope8.1 This test method covers the continuous measurement of sodium in water
30、using a sodium ion electrode.9. Summary of Test Method9.1 Sodium ion electrodes provide consistent logarithmic response over many orders of magnitude of concentration using the same principles as pH electrodes but with different ion selectivity. The electrode signal has a slope of approxi- mately 59
31、 mV/decade change in sodium ion concentration at25C (77F).9.2 Where electrode selectivity and the sodium concentra- tion and pH of the sample require it, this test method includes provision for the addition of pH adjusting reagent to suppress hydrogen ion concentration and assure accurate electrode
32、response to sodium. The lower limit for accurate measurement without reagent appears to be about 1 g/L (1 ppb) in ammonia-treated power plant samples (4).9.3 This test method is particularly adaptable to high purity water and is relatively free of interferences (1). The overall operating cost of thi
33、s system is considerably less than that of continuous flame photometry, and it is more sensitive than electrical conductivity.9.4 The repeatability of this test method is 65 % of the reading.10. Interferences10.1 The sodium ion electrode, like all potentiometric electrode measuring systems, is respo
34、nsive to changes in ion activity and not true concentration changes (that is, the response is to changes in concentration multiplied by an activity coefficient). However, as concentrations approach infinite dilution, activity coefficients approach unity and ion concentration and active ion concentra
35、tion become very nearly equal.10.2 The activity coefficient of sodium ion will vary with changes in the total ionic strength of the solution. Therefore, it is important to maintain either a low or constant ionic strength. A constant flow of pH adjusting reagent generally establishes aconsistent ioni
36、c strength.10.3 The sodium content of pH adjusting reagent, if deliv- ered directly to the sample, must not be significant compared with the lowest concentration being measured. Any air con- tacting the sample must be sodium-free.2D 2791 93 (2001)10.4 The sodium ion electrode is responsive to certai
37、n othermonovalent cations. Interference by silver, lithium, hydrogen, potassium, ammonium, and other ions must be considered. The selectivity to interfering ions varies by electrode manufacturer. In the low-solids water to which this test method applies, silver and lithium ions are usually absent. P
38、otassium ion, often contributed to the sample by the reference electrode, must be carried downstream away from the sodium ion electrode. Ammonium ion, present in many power plant samples, gener- ally does not interfere with measurements greater than 1 g/L(1 ppb). Measurements below 1 g/L use a stron
39、ger base reagent that suppresses the ionization of ammonia.10.5 Elevation of pH so that hydrogen ion concentration is3 to 4 orders of magnitude lower than that for sodium generally makes the electrode response independent of variations in hydrogen ion concentration. Any of the reagents mentioned is
40、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 selectivity allows some measurements in ammoniated power plant samples greater than 1 g/L (1 ppb) sodium without fu
41、rtherreagent addition.10.6 When this test method is used without pH adjusting reagent, the sample pH and sodium concentration must be within the manufacturers guidelines for the particular sodium electrode to assure accurate measurement.10.7 The sodium ion electrode is not subject to interference fr
42、om color, turbidity, colloidal matter, oxidants, and reductants.11. Apparatus11.1 Measuring InstrumentUse commercially available potentiometric specific ion monitors that have expanded-scale operation with adjustable ranges calibrated directly in sodium ion concentration units of micrograms per litr
43、e (parts per billion). Electrical output signals must be isolated from ground and from electrode input and may be scaled for logarithmic, linear, or bilinear ranges.11.2 Sodium Ion ElectrodeUse a commercially available sodium-sensitive electrode (sodium ion electrode). Because electrode selectivitie
44、s vary among manufacturers, care must be taken that the electrode, reagent or lack of it, and sample conditions are compatible (see 10.4, 10.5, and 10.6).11.3 Reference ElectrodeUse a reference electrode com- patible with the measuring electrode.11.3.1 When the sodium ion electrode has a silver-silv
45、er chloride internal half cell, the reference electrode should be silver-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 co
46、rrect for the difference between the measuring electrode and the reference electrode. If the reference electrode filling solution is an interference in the measurement of sodium, then the reference electrode must be downstream from the measuring electrode(see 10.4 and 11.3.2).11.3.2 If calomel electrodes are used, refer to Test Methods D 1293. The electrolyte used in reference electrodes